1

Karen Callahan Honor’s Thesis, 2004

Introduction.

n-Octanol is an important molecule both for biological and environmental

reasons. It has been discovered previously that dilution in solvents and temperature affect

the hydrogen bonding of n-octanol. Here the effects of solvent polarizability and dipole

moment on n-octanol will also be addressed experimentally.

Biological Importance of n-Octanol.

n-Octanol, a liquid at room temperature, is an amphiphilic molecule, that is to say

one end is hydrophilic and the other is hydrophobic (Fig. 1). Due in part to this property,

it is pharmaceutically useful. n-Octanol is a model of phospholipid membranes (1,2,3).

Commonly, an interface is made by layering n-octanol and water to determine to what

extent an anionic compound—medicine or toxin—will be partitioned or absorbed into the

octanol phase or the aqueous phase (Fig. 2). n-Octanol water partitioning shows whether

the compound is likely to be absorbed into the body through skin, lungs, or the gastro-

intestinal tract (uptake), and whether it is likely to accumulate in the body (retention). For

example, if a substance is very hydrophobic it will not absorb into the blood, and is less

likely to spread about the body; however, it is more likely to accumulate in fatty tissues.

Environmental Significance of n-Octanol.

In addition to its pharmaceutical uses, the octanol-water partition coefficient is

also used to determine bioavailability and environmental fate—that is where pollutants

2

end up in ecosystems. Hydrophobic materials are more likely to settle into organic dirt

and sediment than stay in water. Hydrophilic compounds, on the other hand, will be

found more in the aqueous layer of the partition and therefore are more likely to be

absorbed in blood and aqueous body systems. They are also more likely to be found in

water than in sediment (2,3,4).

n-Octanol is also an important model for organic atmospheric aerosols, which

come from many sources, including the oxidized organic emissions of plants, fuel vapors,

and exhaust from incomplete combustion. Organic aerosols can be very complex,

containing hundreds of different compounds made mostly of carbon and hydrogen, but

these aerosols can be approximated for study by model molecules. n-Octanol itself does

not make up a large portion of atmospheric aerosols, but it shares similar properties with

many of the molecules found in organic aerosols. For example, n-octanol has a localized

partial charge and is not very soluble in water (1,5,6).

Why do a Fundamental Study of n-Octanol?

Although n-octanol is used in the research of a large variety of subjects, there

have been only a limited number of studies specifically of the fundamental properties of

n-octanol. H. Z. Zhang et al. have studied the uptake of gas phase acids and gas phase

orgnic molecules by n-octanol as a function of relative humidity (5,6). The results for the

uptake of the acids were that at room temperature in the absence of humidity,

hydrobromic acid was better absorbed into droplets of n-octanol than hydrochloric acid,

but at 50% humidity they absorbed into the n-octanol droplets to the same extent (6).

Secondly, Paola Sassi et al. used Raman and IR studies at different temperatures and at

3

different concentrations in carbon tetrachloride to elucidate the hydrogen bonding

properties of n-octanol. n-Octanol forms cyclic and linear oligomers like lipids form

micelles and bilayers (Fig. 3). There are three main peaks given by different means of

hydrogen bonding: n-octanol accepting two protons and donating one, n-octanol

accepting a proton and donating another, and n-octanol which is at the end of a chain,

which only donates a proton. There are also two conformations given to n-octanol

hydroxyls which are not proton donating, the free OH, and the proton accepting non-

donating OH. These form two components of a peak, which will be addressed in the

second chapter (Fig. 4). Sassi et al. have observed that as the concentration of n-octanol

decreases in CCl4, the peaks corresponding to non-hydrogen-bonded n-octanol grow

relative to those representing hydrogen bonding (1).

Purpose.

The main goal of this project was to show the effect of polarizability of solvent on

the intermolecular interactions of n-octanol. The first part of this project was to reproduce

results from a paper by Paola Sassi et al. study using Raman spectroscopy rather than

infrared spectroscopy to study the effect of dilution of n-octanol with carbon tetrachloride

on hydrogen bonding using Raman spectroscopy rather than infrared spectroscopy. Also,

n-octanol itself at different temperatures was studied with Raman spectroscopy.

Secondly, dilution of n-octanol with other organic halogen solvents was studied. Finally,

n-octanol was studied in the presence of cyclohexane and benzene, two non-halogen-

containing, cyclic, organic solvents to confirm that the effect of polarizability was

consistent in different kinds of solvents.

4

References.

1. Sassi, et al. Structural and Dynamical Investigations of 1-Octanol: a Spectroscopic

Study. Journal of Molecular Liquids. 96-97 (2002) 363-377.

2. Fresta, et al. Combining Molecular Modeling with Experimental Methodologies:

Mechanism of Membrane Permeation and Accumulation of Ofloxacin. Biorganic

& Medicinal Chemistry. 10 (2002) 3871-3889.

3. Rowe, et al. Thermodynamics of Partitioning for a Series of n-Alcohols Determined by

Titration Calorimetry: Role of Hydrophobic Effects. Biochemistry. 37 (1998)

2430-2440.

4. Chemistry Assistance Manual for Premanufacture Notification Submitters. The

United Stated Environmental Protection Agency. 49-59.

5. Zhang et al. Uptake of Gas Phase Species on 1-Octanol: Part 1. Uptake of α-pinene, γ-

Terpinene, ρ-Cymene, and 2-Methyl-2hexanol as a Function of Relative

Humidity

and Temperature. Journal of Physical Chemistry A. 107 (2003) 6388-6397.

6. Zhang et al. Uptake of Gas Phase Species on 1-Octanol: Part 2. Uptake of Hydrogen

Halides and Acetic Acid as a Function of Relative Humidity and Temperature.

Journal of Physical Chemistry A. 107 (2003) 6398-6407.

7. Kreuger, et al. Infrared Spectra: Intramolecular Trans Lone Pair Interaction with α-CH

Bonds and the Stability of Conformers in Alcohols and Thiols. Journal of

Molecular Structure. 5 (1970) 375- 387.

5

Figure 1. n-Octanol is an amphiphilic molecule.

H3C OH

Hydrophobic Tail Hydrophilic Head

6

Figure 2. A partition made of n-octanol and water is used to determine whether a

compound is likely to pass through a biological membrane.

7

Figure 3. Linear and cyclic oligomers are formed by n-octanol. (Sassi et al.)

8

Figure 4. There are three manners of hydrogen bonding in n-octanol, each contributing a

different peak. There are also two contributions towards free OH peaks. This is a Raman

spectrum of n-octanol at 0°C with the hydrogen bonding affecting the respective peaks

superimposed to curves fit by Igor.

8000

6000

4000

2000

0

Ampl

itude

3700360035003400330032003100Wavelength,

-200

0

200

Res

idua

ls

currentpeak

+

~3200 cm-1 ~3320 cm-1

~3475 cm-1

3642 cm-1

9

Chapter 1: Raman Spectroscopy

Part 1: Theory

There are many types of vibrational spectroscopy for the many types of energies

of molecules: rotational, vibrational, electronic transitional, and spin transitional. There

are also spectroscopies based on the different interactions the molecules can have with

energy: absorption, reflection, and scattering. Raman spectroscopy looks at the scattering

of incident photons of visible light by molecules.

A beam of radiation (light, heat, etc) has an electric field that interacts with the

electron cloud of the bonds of molecules in the sample forming a temporarily induced

dipole moment in the bond (1). The ability of the electron cloud to be distorted is called

polarizability. The more polarizable a molecule is, the more the electron clouds of its

bonds are distorted by the incident radiation. The induced dipole moment is equal in

energy to that from Rayleigh, Stokes, and anti-Stokes scattering combined (1). As the

bond emits the scattered light it returns to its original unexcited state. A more polarizable

bond causes more scatter.

There are three ways that photons of light can be scattered by a molecule. When

any given Raman active sample is irradiated, proportions of light will be scattered in

these ways. Rayleigh scattering occurs when a photon of light is elastically scattered by a

molecule. This means that a photon comes from a light source, irradiates the sample and

is then emitted by the sample at the same wavelength, but in a random direction. There is

10

more Rayleigh scattering than any other type of scattering. Unfortunately, since it is the

same wavelength as the source, it does not reveal much about the sample. Stokes

scattering is the next most common type of scattering, though it is far less common than

Rayleigh scattering. Stokes scattering results from a photon exciting an electron from the

ground vibrational state in the ground electronic state to a virtual state related to the

energy of the incident light and then the electron relaxing back to a higher vibrational

state within the ground electronic state and releasing a photon with an energy which is

equal to the incident light minus the energy between the two vibrational states. Stokes

lines are usually the more common of the inelastic scattering bands, because we are

usually taking spectra of molecules at room temperature, where molecules are generally

in the ground vibrational state of the ground excited state. We get information about the

energy between the vibrational states from Stokes lines. The final type of scattering

occurs when the molecules are in an excited vibrational state. Anti-Stokes scattering is

the least common type of scattering. In anti-Stokes scattering, a molecule is already in an

excited vibrational state when the incident photon hits it, raising it to a virtual state. The

electron then relaxes to the ground state, emitting a photon that has the energy of the

incident photon plus the energy between the ground state to which the electron relaxed

and the excited vibrational state where it started. Anti-Stokes scattering is generally not

used because of the weak signal; however, with a sample at a warm enough temperature,

there are more molecules with electrons in excited states (1). The signal from anti-Stokes

scattering will increase in this case. Also, sometimes it is used to look at fine structure in

spectra, which is easier because of the weaker scattering (2).

11

There is a selection rule for each type of molecular spectroscopy, which

determines what molecules, and under what conditions spectra can be obtained. For

example, to obtain an IR spectrum the molecule must contain a dipole moment, and the

dipole moment must change when the molecule vibrates in a given way for that vibration

in the molecule to be IR active. Raman activity is similar; the selection rule for Raman

activity is that the polarizability, the ability of the electron cloud to be distorted by the

electric field of the incident beam of radiation, must change with the distance between

nuclei of the sample molecules (1,3). The electron cloud is more easily distorted when

bonds are long or when the electrons are farther from the nucleus (eg. chlorine, bromine,

iodine in order of increasing polarizability). There are different motions of the molecule-

twisting, bending, wagging, stretching, etc., which may be Raman modes in a molecule if

they cause a change in polarizability.

There are advantages to Raman spectroscopy over IR spectroscopy and other

spectroscopies. The signal from water is not nearly as strong in Raman as it is in IR (1, 4,

5, 6). Water in samples swamps out other signals in IR, but the water signal is not very

strong for Raman spectroscopy. So Raman spectroscopy can be used for examining

aqueous samples. Raman spectroscopy can be done with glass vials since the incident

beam and Stokes bands are visible light. Glass is much less expensive than other

materials, but absorbs in the ultra-violet and infrared regions, limiting its uses (1, 5). For

these experiments, the greatest advantage of Raman spectroscopy over IR is that because

of the difference in selection rules (change in polarizability as opposed to change in

permanent dipole moment) the strength of the relatively weak free OH band is much

12

larger in proportion to the hydrogen bonding OH bands in Raman Spectroscopy than in

IR (7).

Part 2: The Raman Set-up Used for These Experiments.

The parts of the Raman set-up include the source of incident radiation, the sample

cell, the filters, the monochromator and associated controllers and motors, the entrance

slit to the monochromator, the detector and associated controllers, and the fiber optics

that carry light from the source to the sample and signal from the sample to the

monochromator, the charge-coupled detector, the transducer and the software.

The source of radiation for the Raman system used was a frequency-doubled

Nd/YAG laser providing 532 nm radiation. This is monochromatic green light. There are

two filter wheels to control the amount of power in the incident beam going to the fiber

optic probe (and thus the sample). The experiments were done with 20-86mW of power

exiting the probe to the sample.

The sample cells were 1.8 mL Qorpak glass vials with Teflon-lined caps to

prevent the organic compounds from decaying the plastic and escaping.

Within the probe, there is a band-pass filter that only allows light of the excitation

wavelength, 532 nm, and not Raman scatter from the silica of the fiber optics, to exit the

probe and reach the sample. The laser light passes through the dichroic filter, but the

light from the sample is reflected by it up to another set of lenses and filters leading to the

fiber optic that carries it to the monochromator. The scattered light from the sample is

collected at 360º. There is a long-pass filter before the sample reaches the fiber optic

13

going to the monochromator, which prevents the Rayleigh scatter and anti-Stokes scatter

from reaching the monochromator. The probe also contains collimating lenses, which

focus the incident beam and the signal, and mirrors, which allow for the some of the same

path to be used both for sending the incident beam and collecting scatter from the sample

(8).

The slit into the monochromator is controlled by a micrometer, which opens and

closes it. For these experiments the slit was 20-100 X 10-6 m wide. A larger entrance and

exit slit width will increase signal. A larger exit slit width will also allow a wider range of

wavelengths to enter the detector. This will increase noise and reduce resolution. An

imaging fiber coupler is used to enhance the collection efficiency of the scatter going to

the monochromator from the fiber optic.

The monochromator is used to separate the wavelengths of the collected light (in

this case Raman scatter) and separate it into its different wavelengths that exit through a

narrow slit to provide a narrow bandwidth of light for the detector. The monochromator

has three grating that can be used: 600 grooves/mm, 1200 grooves/mm, and 1800

grooves/mm. 600 grooves/mm collects a larger range of wavelengths at a time, but has a

much lower resolving power then the gratings with denser grooves. That is, the difference

in two wavelengths must be more for the two to be distinguished from each other than

with a denser grating.

After passing through the monochromator, the signal goes through the exit slit,

which determines the wavenumber, to the detector, which is a charge-coupled device. In

general, this type of detector is a two-dimensional array of pixels each made of three

electrodes with a negative charge on them on top a layer of silica insulator. On the other

14

side of the insulating silica, is silicon with non-bonding electrons (n-type semiconductor).

When photons strike the electrodes, holes (absence of electrons) are formed under the

electrodes and collect there, forming "potential wells" while electrons collect in the n-

type silicon. The charge thus created is shifted to a high-speed register and preamplified

before being processed and sent to the computer as a digital signal. The pixels are

transducers (detectors), converting the photons that hit them into charges (1).

The software is Spectrasense. It allows the computer to control position of the

monochromator, the acquisition time, the number of reads per cycle, and a few other

features about collecting data through controllers and motors. In addition, it combines the

position data from the monochromator and the signal data from the CCD into charts

called spectra that are the readouts understood by humans.

Part Three: Signal and Noise and Things that Affect Them.

There are many things which affect the signal to noise ratio. Only the ones used in

this work will be touched on here. There are many origins of noise, noise from the

sample, noise from the system, and noise from outside the system are three

generalizations.

Signal of individual peaks were increased and noise diminished by cooling the

sample, generally to 0ºC in an ice bath. This reduced the rotational excitations present,

resulting in stronger, narrower vibrational peaks. The signal peaks were less intense, but

the noise was reduced more significantly. Cooling samples helps to distinguish when

there are two or more peaks close together because the peaks are narrower than at room

temperature (1).

15

Within the system and protocol there are many things that can be done to reduce

noise. The CCD device is cooled with liquid nitrogen to 77K to reduce thermal noise

caused by electrical resistance in the detector. The entrance slit to the monochromator can

be narrowed allowing only wavelengths of a certain range of length to enter. Longer

acquisition times can be used to collect more light, leading to a stronger signal relative to

the noise. Many spectra can be averaged together to increase the signal to noise ratio by

square root of the number of spectra or reads. Lasers of lower wavelengths produce

stronger scattering, though they are also more likely to produce fluorescence or even

decomposition of the sample. 532nm did not cause the samples to decompose or

fluoresce (with the notable exceptions of CBr4 and CHBr3) and was a short enough

wavelength to cause a sufficiently detectable amount of scatter. The power of the laser

will also affect the strength of the scatter to a point. It also increases the noise and so

increasing the power is only helpful to a point. The quantum efficiency of the detector in

the region of the signal is also important for reducing signal to noise. If the detector isn't

very sensitive in a given region the signal will be diminished.

Isolating the system as much as possible can reduce the noise from outside

sources. For example, having thick concrete walls around and above the lab limits the

radiation from outside reaching the lab. Having a solid floor limits the vibrations felt by

the apparatus. Keeping the system enclosed in matte black boxes limits the amount of

light that goes in from outside sources, and also the amount of light that gets out, the

latter not affecting the signal to noise ratio, but being important for safety reasons. In

short, there are many ways to reduce noise (1).

16

References.

1.Skoog, Holler, Neiman. Principles of Instrumental Analysis. 5th ed. Harcourt Brace

College Publishers: Philadelphia, 1998.

2.Laserna, Javier. An introduction to Raman spectroscopy: Introduction and basic

principles. Department of Analytical Chemistry University of Malaga, Spain.

Last Updated August 6, 2001.

http://www.spectroscopynow.com/Spy/basehtml/SpyH/1,1181,6-14-9-0-0-

education_dets-0-2902,00.html

3. Banwell, C. N. Fundamentals of Molecular Spectroscopy. McGraw-Hill Publishing

Limited: London, 1966.

4. Bellamy, L. J. The infrared spectra of complex molecules. 3 ed. Chapman and Hall:

London, 1975.

5. Collette, T. W. and T. L. Williams. The role of Raman spectroscopy in the

analytical chemistry of potable water. Journal of Environmental Monitoring. 4

(2002) 27-34.

6. Crews, Rodriguez, and Jaspars. Organic Structure Analysis. Oxford University

Press: New York, 1998.

7. Sassi, et al. Structural and Dynamical Investigations of 1-Octanol: a Spectroscopic

Study. Journal of Molecular Liquids. 96-97 (2002) 363-377.

8. InPhotonics. Background filtering in fiber optic Raman sampling probes. Technical

17

Note #13. InPhotonics Inc.: Norwood, MA, 1999.

www.inphotonics.com

Figure 1. Rayleigh, Stokes, and anti-Stokes scattering.

A. Spectrum of the Rayleigh, Stokes, and anti-Stokes scattering of CCl4 (Skoog et al. pp.

430).

B. Energy level diagrams of

i. Rayleigh Scattering ii. Stokes Scattering iii. Anti-Stokes Scattering

EE E

18

Figure 2. Changes of polarizability of molecule with vibration-- CCl4.

yy

Cl

Cl

Cl

Cl

Cl

Cl

Cl

Cl

Cl

Cl

Cl

Cl

19

Figure 3. A diagram of the Raman set-up used for the experiments.

Computer Software: SpectraSense

Laser, Filters

Laser controller

Monochromator

Liquid N2 cooled CCD

Probe

Fiber optic cable Sample Box

Micrometer and imaging fiber coupler

20

Chapter 2: n-Octanol

n-Octanol not only has the hydrogen bonding due to its polar hydroxyl group, but

due to the size of its hydrophobic chain, non-hydrogen-bonded hydroxyl groups or free

OH configurations can be seen in the spectra of pure liquid n-octanol. For the smaller

alcohols, it is necessary they be either in the vapor phase or highly diluted in non-polar

solvent (1). Raman spectroscopy is a more sensitive technique than infrared spectroscopy

for detecting the monomer band, though all the OH bands are weaker in Raman

spectroscopy than infrared spectroscopy (2). There are three sets of peaks that will be

addressed in the OH region of the spectrum (~3100-3700 cm-1): the peaks due to the free

OH configurations (monomer band), the peaks due to hydrogen bonding configurations,

and the peak which is sometimes noticeable at a slightly higher wavenumber than the

monomer band. Then, Raman isotropic and anisotropic spectra from a paper by Sassi et

al. will be compared to non-polarized spectra taken with the laser system described in the

previous chapter.

The Free OH Band.

There are generally held to be either two or three components to the free OH (or

monomer) band of an alcohol. In the paper by Sassi et al. two bands are assigned to trans

and gauche rotational isomers and the third to proton-accepting, non-proton-donating

21

hydroxyls (2). The trans rotational isomer is assigned to ~3640 cm-1 and the gauche

rotational isomer is assigned to ~3625 cm-1 (2). The difference in position of the

rotational isomers is due to interactions between the lone pair electrons on the oxygen

and the CH bonds on the carbon containing the oxygen. When a C-H bond is trans to a

C-O bond the lone pair of the oxygen interacts with the anti-bonding orbital of the C-H

bond lowering the frequency of the OH stretch as the C-O bond becomes slightly more

double bond-like (1,3). (Fig 1.) The component from the proton-accepting hydroxyl is so

close to the monomer components that it cannot be distinguished (2).

The Hydrogen Bonding Components.

There are three configurations of hydrogen-bonding hydroxyls. The hydrogen

bonds are not permanent, but rather they are constantly breaking and reforming, while

maintaining an average composition of the different types of configurations (2). The

single proton donors are assigned to 3500cm-1, the proton donor- proton acceptors are

assigned to 3300-3400cm-1, and the proton donor- double proton acceptors are assigned

to 3190cm-1 (2, 4, 5). The shift in frequency of the O-H bond from the monomer band

corresponds to the energy of the hydrogen bond (6). Furthermore, the shift in frequency

from the monomer band has an approximately linear relationship with the distance

between the oxygen of a proton donor and the oxygen of the proton acceptor of a

hydrogen bond. The more an O-H bond is involved in hydrogen bonding the weaker,

longer, and less energetic it is, and the lower the wavenumber of the Stokes band of light

it scatters. The hydrogen bonds in n-octanol are not permanent, but rather they are

constantly breaking and reforming, but maintaining an average composition of the

22

different types of configurations (2). Intermolecular hydrogen bonds are broken or

lessened with increase in temperature, or dilution by non-polar solvents.

The broad band near the monomer band.

This band is present in water, methanol, ethanol, octanol, and probably other

alcohols (2, 4, 6). It has been assigned to a number of very different things, and is open to

interpretation. It has been assigned to "the fourth harmonic band of the C-H frequencies

(6)." Also, less relevantly, it has been assigned signal from oriented vapor and

interference in Sum Frequency spectra (7). But it seems that it is generally not discussed

(1, 2, 4).

Comparison of Spectra at Room Temperature.

A Raman spectrum was taken of pure n-octanol at room temperature and curve

fitted by Igor to give Chi2 = 7.1859 X 106 (Fig 2). This yielded three hydrogen bonding

components, 3268 cm-1, 3348 cm-1, and 3463 cm-1. The largest was the component

corresponding to a blue shifted (to higher energy) proton donating- double proton

accepting hydroxyls. This is inconsistent with common sense, as well as the data of Sassi

et al (Fig. 3). In their data the largest contributor to the hydrogen-bonded peaks is the

proton donor- single proton acceptor. It seems unreasonable that there would be less

proton donor- single proton acceptor than either proton donor or proton donor-double

acceptor, or more simply, one would not expect n-octanols in solution to mostly be part

of one or three hydrogen bonds. One would expect n-octanols to be involved in mostly

23

either one and two, or two and three hydrogen bonds in a solution. It is important to note

that the components are all very broad, that many different solutions are possible to fit the

spectrum, and thus curve-fitting may not always be accurate. It is possible in this case

that the CH stretch, broadened at room temperature, is not completely taken into account

in the curve-fit which may cause the perceived error.

The free OH peak for the non-polarized and isotropic profiles agreed within

approximately 1.5cm-1, which is likely within the resolutions of the two different

systems.

Comparison of Spectra at Colder Temperatures.

15 Raman spectra of pure n-octanol at 0°C were taken and signal averaged. They

were fit with Igor to give the following peaks: 3208 cm-1, 3315 cm-1, 3473 cm-1, and

3641.71 +/- 0.49 cm-1. Chi2= 7.10201 X 105. The proton donor- single acceptor was the

largest peak, though not much larger than the proton donor, or single proton-donor

double acceptor (Fig. 4).

10 Raman spectra of pure n-octanol at 4°C were taken and signal averaged. They

were fit with Igor to give the following peaks: 3208 cm-1, 3319 cm-1, 3474 cm-1, and

3641.56+/- 0.33 cm-1. Chi2=4.94773 X 106 (Fig. 5). The proton donor- single acceptor

was, again, the largest component followed by the proton donor, and then the proton

donor- double proton acceptor. There was a broad band that fit in this spectrum just blue

of monomer band (~3655 cm-1). Its origin is unknown, though it could perhaps even be a

tail from the hydrogen bonding components.

24

These spectra are fairly consistent with the spectra at 10°C from the paper by

Sassi et al. (Fig. 6). The components from hydrogen bonding configurations, particularly

proton donor and proton donor- single acceptor shift to lower energy with the decrease in

temperature from where they would be at room temperature. Further the fits are

reasonable with regard to the area they attribute to each of the hydrogen-bonding

configurations.

25

References.

1. Bellamy, L. J. The infrared spectra of complex molecules. 3 ed. Chapman and Hall:

London, 1975.

2. Sassi, Paola, et al. Structural and dynamical investigations of 1-octanol: a

spectroscopic study. Journal of Molecular Liquids. 96-97 (2002) 363-377.

3. Kreuger, P. J., Jan, and Wieser. Infrared spectra: Intramolecular trans lone pair

interaction with α-CH bonds and the stability of conformers in alcohols and

thiols. Journal of Molecular Structure. 5 (1970) 375-387.

4. Graener, H., Ye, and Laubereau. Ultrafast dynamics of hydrogen bonds directly

observed by time-resolved infrared spectroscopy. Journal of Chemical Physics.

90 (1989) 3413-3416.

5. Graener, H. Ye, and Laubereau. Ultrafast vibrational predissociation of hydrogen

bonds: Mode selective infrared photochemistry in liquids. Journal of Chemical

Physics. 91 (1989) 1043-1046.

6. Badger, Richard M. and Simon H. Bauer. Spectroscopic studies of the hydrogen bond.

II. The shift of the O-H vibrational frequency in the formation of the hydrogen

bond. Journal of Chemical Physics. 5 (1937) 839-851.

7. Allen, H. C., E. A. Raymond, and G. L. Richmond. Non-linear vibrational sum

26

frequency spectroscopy of atmospherically relevant molecules at aqueous solution

surfaces. Current Opinion in Colloid & Interface Science. 5 (2000) 74-80.

Figure 1. Trans and gauche rotational isomers of n-octanol. A. Newman Projection. B. Sawhorse projection. A.

B.

27

OO

H

H H

H

H H

GaucheTrans Figure 2. n-Octanol at Room Temperature. Raman spectra with curve-fitting done by Igor and Chi2 minimized.

28

12x103

10

8

6

4

2

0

Ampl

itude

3700360035003400330032003100Wavelength,

-400

0

400R

esid

uals

currentpeak

Figure 3. Raman spectra of n-Octanol at room temperature (Sassi et al.)

+

3268 cm-1 3348 cm-1

3463 cm-1

3639.43 +/- 0.55 cm-1

Wavenumber (cm-1)

29

Figure 4. n-Octanol at 0°C. Raman spectra with curve-fitting done by Igor and Chi2 minimized.

+

3190 cm-1 3300-3400 cm-1 3500 cm-1

~3631 cm-1

~ 3638 cm-1

30

8000

6000

4000

2000

0

Ampl

itude

3700360035003400330032003100Wavelength,

-200

0

200R

esid

uals

currentpeak

Figure 5. n-Octanol at 4°C. Raman spectra with curve-fitting done by Igor and Chi2 minimized.

+

3208 cm-1 3315 cm-1 3473 cm-1

3641.71 +/- 0.49 cm-1

Wavenumber (cm-1)

31

20x103

15

10

5

0

Ampl

itude

38003700360035003400330032003100Wavelength,

-400

0

400R

esid

uals

currentpeak

Figure 6. Raman spectra of n-Octanol at 10°C. (Sassi et al.)

+ 3208 cm-1

3319 cm-1

3474 cm-1

3641.56 +/- 0.33 cm-1

3655 cm-1 (broad curve)

Wavenumber (cm-1)

32

Chapter 3: the Effect of concentration on the free OH peak of n-octanol

33

Spectra were taken of the hydrogen-bonding region of n-octanol at different

concentrations (moles/ liter) in carbon tetrachloride at room temperature (23°C) and 4°C.

The carbon tetrachloride components of the spectra were subtracted out of the solution

spectra with n-octanol and the resulting graphs were curve fitted with Igor to determine

the position (cm-1) and size (area and amplitude) of peaks (Fig. 1). These are compared to

the curve-fitted spectrum of pure n-octanol (Fig. 2). Please note the "current peak" is an

artifact of the program.

In the curve fitted spectrum of 99+% pure n-octanol at room temperature there are

three components to the hydrogen-bonded peak corresponding to three conformations:

proton donor, proton donor- proton acceptor, and proton donor-double proton acceptor.

The component with the lowest wavenumber is the one with the lowest energy, longest

O-H bond, the proton donor- double proton acceptor. This peak occurs around 3250 cm-1

in n-octanol at room temperature. The component around 3350 cm-1 corresponds to single

proton donor- proton acceptors. The component that has a maximum near 3500 cm-1

corresponds to the single proton donors. These three peak components collectively

correspond to the O-H hydrogen bonded stretches of n-octanol. There is also a peak

centered at 3639.62 +/- 0.53cm-1 at 23°C, and 3641 cm-1 at 4°C, which corresponds to the

O-H stretch of nonproton-donating n-octanol (Fig. 3).

Five different concentrations of n-octanol in carbon tetrachloride were used at

23°C (Fig. 4). They are presented in molarity, M (moles/liter) and mole fraction, X

(moles n-octanol/ total moles in solution). In 0.05X (0.5M) n-octanol in CCl4 hydrogen

bonding is present, but the hydrogen bonding peaks will only be fit to two peaks, not

three as are in present in pure n-octanol. In fact, if you try to force the Igor curve fitting

34

program to use three curves in the hydrogen bonding area, one will show up as a flat line.

This could be because the curve is very broad and the signal is not very strong. The free

OH peak is at 3637.48 +/- 0.28 cm-1; this is approximately two wavenumbers less than

the free OH peak of pure n-octanol taken on the same day and under the same conditions.

0.001X n-octanol in CCl4 and all the lower concentrations do not show any detectable

hydrogen bonding over the noise of the spectra. The free OH peak for the 0.001X

solution is centered at 3637.76 +/- 0.53 cm-1. The free OH peaks for the remaining

concentrations are: 3637.85 +/- 0.79 cm-1 for 0.005X, 3638.96 +/- 1.41 cm-1 for 0.002X,

and no detectable signal over the noise for 0.0005X n-octanol in CCl4. In Raman

spectroscopy the areas of the peaks are generally proportional to the concentration of the

species present. Area of the free OH peak was plotted against concentration in mole

fraction of n-octanol of these solutions and also of pure n-octanol (Fig. 6). It was found

that the areas of the free OH peaks of the lowest four concentrations (0.01X and below)

with respect to concentration could be fitted to a straight line with a y intercept of 0, and

have R2= 0.9948. R2 of greater than 0.99 generally suggests good agreement, perfect

agreement of observations with a regression line would be R2=1.00 (Fig. 7). However,

the area of the free OH peak for 0.05X n-octanol in CCl4 was far less than the regression

line would predict based on the lower concentrations, and the area of the free OH peak

for pure n-octanol was actually less than for 0.05X n-octanol. This is because some of the

OH from 0.05X is involved in hydrogen bonding. Much of the OH from pure n-octanol is

involved in hydrogen bonding. The amount of hydrogen bonding increases with the

concentration after some minimum concentration between 0.05X and 0.01X is reached.

35

The data for n-octanol in CCl4 was reproduced at 4°C for three concentrations:

0.05X, 0.01X, and 0.005X (Fig. 7,8). 0.05X n-octanol in CCl4 at 4°C showed three

hydrogen bonding components: ~3140 cm-1, ~3270 cm-1, and 3495 +/- 1.96cm-1. This

middle component, which is assigned to proton donor- single proton acceptor, is the

largest. The free OH peak is at 3637.42 +/- 0.16 cm-1. The 0.01X solution of n-octanol in

CCl4 has hydrogen bonding in contrast to the same solution at 23°C. The three peaks due

to the different hydrogen bonding configurations are: ~3170cm-1, ~3290cm-1, and 3513

+/- 2.82 cm-1. The free OH peak is at 3637.74 +/- 0.19 cm-1. In the 0.005X solution of n-

octanol in CCl4 no hydrogen bonding was visible. The free OH peak was at 3638.13 +/-

0.22 cm-1.

Comparing the data for n-octanol at 23°C and 4°C, there are a few things to note.

The minimum concentration at which n-octanol starts forming hydrogen bonds with in

the detection limit of this system is lower at 4°C than at 23°C. If there is a shift in the free

OH peak with either temperature or increasing dilution (0.05X and lower) in CCl4 it is

less than the resolution of the system (1-2 cm-1 depending on conditions like slit widths

and wavenumber range).

In addition to comparing the OH region of the spectra for different concentrations

of n-octanol in CCl4, other solvents—CBrCl3 and CHCl3 were used for comparison at

4°C. CBrCl3 is more polarizable than CCl4, and it has a slight dipole. CHCl3 is less

polarizable than CCl4 and it has a very strong dipole. CCl4 has no molecular dipole.

CBrCl3 has a lot of structure in the OH region (3100-3700 cm-1) of the spectrum.

It also has unpredictable backgrounds that do not appear to be reproducible, but may be

due to fluorescence and affected by the presence of n-octanol (Fig. 9). This especially

36

affects where the hydrogen-bonding peaks normally are. As such, the only information

that can be reliably taken from these spectra is the free OH peak. The free OH peaks for

0.05X, 0.01X, and 0.005 X are at 3630.24 +/- 1.15 cm-1, 3629.84 +/- 0.25 cm-1, and

3629.45 +/- 0.47 cm-1, respectively. Looking at the graph of area of the free OH peak and

concentration versus OH, there is definitely hydrogen bonding in the 0.05X solution, as

seen by the non-linearity of a plot of area of free OH against concentration of n-octanol in

CBrCl3 (Fig. 10). Though, without more data points one cannot say whether there is

hydrogen bonding in the 0.01X solution.

CHCl3 was used as an alternative organic halogen solvent to CCl4 at 4°C. The

hydrogen gives it a molecular dipole as well as making it less polarizable. The mole

fraction of CHCl3 corresponding to a solution of n-octanol in CHCl3 was subtracted from

the solution spectra. This didn’t appear to work well for 0.01X and 0.005X n-octanol

solutions, but for the 0.05X n-octanol solution the spectrum was flat in the OH region

(Fig 11). This suggests two things. Firstly, that there is very little, if any, hydrogen

bonding in the 0.05X solution of n-octanol in CHCl3. Secondly it suggests that there is

some fluorescence in the CHCl3 that concentrations of 0.05X limit, but lower

concentrations of n-octanol in solution do not. Plotting the area of the free OH peak

against the concentration gives a line with R2 = 0.9997 (Fig 12). The agreement of this

line and the fact that it contains points for all three concentrations suggests that the

minimum concentration for hydrogen bonding of n-octanol has not been reached even at

0.05X n-octanol. The free OH peaks for the solutions are fit with a curve-fitting program

to be 3626.03 +/- 0.06 cm-1, 3626.18 +/- 0.16 cm-1, and 3626.45 +/- 0.31 cm-1, for 0.05X,

37

0.01X, and 0.005X, respectively. The differences in these are below the resolution of the

instrument.

38

Figure 1. Top: Spectra of n-octanol in CCl4 at 4°C.

Bottom: Spectra of n-octanol in CCl4 at 4°C with the mole fraction of CCl4 times the

intensity of each peak on the CCl4 spectrum subtracted off.

5000

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CCl4 0.005X n-octanol 0.01X n-octanol 0.05X n-octanol

39

Figure 2. Curve-fitted spectrum of n-octanol at 23°C, and parameters.

Chi2 7.1859 X 106 Gaussian peaks Peak#1: position= 3268.28+/-7.37443, area= -1.64663e+06+/--837775, width (fwhm)= -255.84+/-46.9156, amplitude= 6046.37, width= -153.64 Peak#2: position= 3347.56+/-3.42417, area= 81089.2+/-65455.6, width (fwhm)= 101.544+/-17.1643, amplitude= 750.204, width= 60.9831 Peak#3: position= 3462.68+/-8.88496, area= 285084+/-75643.2, width (fwhm)= 147.199+/-7.4828, amplitude= 1819.43, width= 58.402 Peak#4: position= 3639.43+/-0.549413, area= 15156.8+/-1356.56, width (fwhm)= 27.0046+/-1.71681, amplitude= 527.277, width= 16.2179

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Figure 3. Curve-fitted spectrum of n-octanol at 4°C and parameters.

Chi2 = 4.94773 X 106 For Gaussian peaks: Peak#1: position= 3318.55+/-2.62775, area= -1.69918e+06+/--323144, width (fwhm)= -174.457+/-19.4339, amplitude= 9149.93, width= -104.772 Peak#2: position= 3207.5+/-3.45092, area= 535780+/-205105, width (fwhm)= 124.727+/-8.86477, amplitude= 4035.48, width= 74.906 Peak#3: position= 3473.78+/-14.9713, area= 938550+/-321216, width (fwhm)= 184.329+/-24.3155, amplitude= 4783.36, width= 110.701 Peak#4: position= 3641.56+/-0.332188, area= 20101+/-1074.86, width (fwhm)= 27.5905+/-1.02116, amplitude= 684.425, width=16.5698 Peak#5: position= 3655.27+/-4.6385, area= 279075+/-98055.9, width (fwhm)= 150.834+/-15.5566, amplitude= 1738.16, width= 90.5849

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0.0005X n-octanol

0.002X n-octanol 0.005X n-octanol

0.01X n-octanol

Figure 4. Spectra of n-octanol in CCl4 at 23°C curve fit with Igor.

Wavenumber (cm-1) Wavenumber (cm-1)

Wavenumber (cm-1) Wavenumber (cm-1)

Wavenumber (cm-1)

42

Figure 5. A. A plot of the area of free OH peaks from Figure 4 against concentration (X).

0.005M - 0.5M n-Octanol

0

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

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43

Figure 6. A plot of area of free OH peaks versus concentration (0.005-0.1M, or 0.0005-

0.01X) with y intercept set to 0,0.

y = 95422xR2 = 0.9948

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Figure 7. Spectra of n-octanol in CCl4 at 4°C curve fit with Igor.

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45

Figure 8. A graph of the area of the free OH peak of n-octanol versus concentration (X)

in CCl4.

0

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46

Figure 9. Spectra of n-octanol in CBrCl3 at 4°C.

N-octanol in CBrCl3

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47

Figure 10. A graph of the area of the free OH peak against concentration (X) for n-

octanol in solution with CBrCl3 at 4°C.

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48

Figure 11. Spectra of n-octanol in CHCl3 at 4°C curve-fitted with Igor.

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Wavenumber (cm-1)

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49

Figure 12. A plot of the area under the free OH curve against concentration (X) for n-

octanol in CHCl3 at 4°C.

y = 2E+06x + 8996.4R2 = 0.9997

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50

Chapter 4: A Comparison of 0.050X n-Octanol in a Variety of Solvents.

Part One: Comparison of the OH Region

Spectra were taken at 23°C of 0.050X n-octanol in solution with each of the

following solvents: carbon tetrachloride (CCl4), bromotrichloromethane (CBrCl3),

benzene (C6H6), and cyclohexane (C6H12). The spectra, which the average of ten 15-

second acquisitions, were curve-fit with Igor, the free OH peak was fit to both one and

two peaks with the base line of each spectra taken into account by the program. The

position, area, width, and (fwhm)—full width-half max, amplitude, and width at the base

were recorded for each peak. The Chi2 value, a measure of error, which one wishes to

minimize, was reported for each fit. The fitted spectra have been included as Figures 1-

16. (Please note, “current peak” is an artifact of the program.)

The Organic Halogen Solvents.

Figure 17 is a table comparing the positions and areas of the free OH peak,

assuming they are all made of only one component, by solvent, and listing the solvent’s

dipole moment and polarizability as available. CBrCl3 is more polarizable than CCl4,

because bromine is more polarizable than chlorine. CBrCl3 and CCl4 have similar dipole

moments (0.21 and 0.1, respectively) in comparison to CCl4 (0.1) and CHCl3 (~1.1), so it

is likely that polarizability rather than dipole moment is what causes most of the

difference observed for the free OH peak when solvated with CCl4 and CBrCl3 (1, 2). As

shown by Figure 18, mole fraction of CBrCl3 was set against peak position for five

51

0.050X solutions of n-octanol in CBrCl3 and CCl4. This fits a linear distribution, but may

have non-linear character, which would be more evident if further experiments were done

to add data for more different concentrations. The comparison is similar to a comparison

of peak position versus polarizability. A more polarizable solvent, or combination of

solvents caused a red shift in the free OH position (to lower energy), while a less

polarizable solvent may cause a blue shift in the free OH peak (an OH bond with higher

energy). The area of the free OH peak (assuming only one component) was also set

against the mole fraction of CBrCl3 (Fig. 19). It was determined that this is very likely a

non-linear relationship, as per R2=0.8997. If this data were reproduced with a greater

variety of concentrations the nature of the relationship would be more apparent.

The Non-Halogenated Solvents.

A possible example of a blue shift of the free OH peak of n-octanol in a less

polarizable solvent might be in cyclohexane, though it falls just below the resolution of

the measurement. As the main difference (in terms of polarizability) between

cyclohexane and n-octanol is an oxygen, this is not unreasonable. It is also possible that

hydrophobic interactions between the hydrocarbon chain of n-octanol and cyclohexane

affect the shift somehow.

On the other hand, the free OH peak of n-octanol in benzene has a very significant

red shift. One thing of note is that in benzene the free OH peak (3614.9 +/- 0.195723 cm-

1) falls far to the red of the free OH peak in CCl4 (3638.02 +/- 0.18571 cm-1). While

benzene has no dipole moment, this may be due to its quadrapole, and/or to the way the

n-octanol is oriented with the benzene and interacts with the ring. Benzene’s ring of

52

alternating double bonds creates an induced magnetic field when a magnetic field is

applied, which is well know in Nuclear Magnetic Resonance (NMR) to produce chemical

shifts of atoms on NMR spectra based on where they are around the induced magnetic

field (4). Light is electromagnetic radiation, having both electric and magnetic properties.

Perhaps there is a similar induced magnetic field in the solution with benzene caused by

the light from the laser and this is what causes the shift in frequency. If this is true, than

the shift will be specific to the orientation of n-octanol around the benzene. Also there

should be two distinct sets of free OH peaks, one shifted red and one shifted blue,

assuming the molecules do not prefer one orientation to the exclusion of the other. There

are not two free OH peaks in the spectra of 0.050X n-octanol in benzene of sufficiently

different energies to account for this. However, the concentration is low; if orientation

perpendicular to the ring is indeed preferred n-octanol parallel to the ring may not be

present in detectable amounts. More work will need to be done in order to determine the

nature of solvation of n-octanol by benzene. If the shift is due to orientation, it probably

cannot be treated as due to a uniform field or continuum; or perhaps, though a continuum

may not accurately describe what is happening, the cause of the shift can be treated as a

continuum for low concentrations of n-octanol. In Chapter Three a similar, though

smaller shift to the red was seen for the free OH peak of n-octanol in CHCl3 (3626.18 +/-

0.16 cm-1) and the cause of it is likely the dipole moment of the solvent, and perhaps

hydrogen bonding of the solvent to the solute. The polarizability of CHCl3 is slightly less

than that of CCl4 (5), which is why it seems reasonable that in this case dipole moment is

what affects the shift.

53

The area of the benzene shift is large in comparison to the free OH peak of n-

octanol in other solvents, including in CHCl3, which was determined to not have

detectable hydrogen bonding (Chapter 3). This suggests strongly that somehow by being

solvated in benzene the free OH peak scatter of n-octanol is being amplified.

Fitting the Free OH Peak to Two Components.

Most of the free OH peaks of n-octanol in the different solvents fit easily to either

one or two peaks (Fig. 1-16). The exceptions are pure n-octanol and 0.050X n-octanol in

a solution of 0.475X CBrCl3 in CCl4. In the case of n-octanol two peaks resulting from

rotational isomers being close together and of such a difference in size that the smaller

one was not detected over the resolution of the experiment. In the 0.050X n-octanol

solution it is possible that the difficulty to fit similar peaks to those in other solvents is

due to there being many peaks from influence of the two solvents both in high

concentrations.

In the 0.050X n-octanol solutions of CCl4, CBrCl3, 0.0994X CBrCl3 in CCl4, and

0.0373X CBrCl3 in CCl4, two components were fit to the free OH peak. The higher-

energy component was smaller for each of these. The areas of both the higher-energy and

lower-energy components were graphed versus mole fraction of CBrCl3 in CCl4 (Fig. 20).

The positions of both components were similarly graphed (Fig. 21). It would require

more data to determine if these relationships are linear or not. While signal for n-octanol

in CCl4 can be fit to two bands, one centered at 3636.35 cm-1, and the other at 3643.07

cm-1, these were not the locations of the corresponding peaks assigned by Sassi et al. with

FTIR: 3640 cm-1 and 3625 cm-1. In addition, curve-fitting to get areas in cases where

54

there is overlap of peaks, especially to this degree should be verified by some other

means. There is any number of combinations of different component positions, areas, and

shapes that can be added to give very similar results, which means that data obtained by

this method should be confirmed some other way.

Spectra of 0.050X n-octanol in benzene are unusual because the lower-energy

rotational isomer component (3613.76 +/- 0.469352 cm-1) is much larger then the higher-

energy (3632.22 +/- 0.709424 cm-1) free OH component. This might be due to there

being a preferred configuration of n-octanol about benzene.

The spectra of 0.050X n-octanol in cyclohexane are also unusual. Its free OH

splits almost evenly into two peaks. This suggests that neither rotational isomer is

preferred in this one case. Perhaps it means that this one solvent doesn’t interact with the

hydroxyl at all, or that it reacts to make both rotational isomers almost equally preferred.

This would also indicate that n-octanol has a greater effect on the n-octanol it solvates

than cyclohexane does (if you were to think of a 0.050X solution of n-octanol in n-

octanol). It would mean that interaction with solvent is something that causes one

rotational isomer to be more common than another.

Part Two: Comparison of the CH region.

In looking at the rest of the Raman Spectrum (~0 cm-1 to 3100cm-1) there was

only one region where the difference in peaks between pure n-octanol and 0.050X n-

octanol was clearly not because of overlap with solvent components. This was the CH

stretching region (Fig. 22). There were no definite shifts in peak position. It could be fit

different ways, but what is noticeable is that some difference in contributions causes a

55

change in intensity at 2936 cm-1 (Figs. 23-25). The spectra have been fit to 5 peaks,

though some other method shall have to be used to determine if there are five peaks or

really some larger number. There is agreement for certain in the leftmost and rightmost

peaks. The middle peaks may shift depending on the solvent, but as the number of peaks

is not well understood, nothing can be said about their positions.

56

References. 1.McClellan, A. L. Tables of Experimental Dipole Moments. W. H. Freeman and

Company, San Francisco, 1963.

2.McClellan, A. L. Tables of Experimental Dipole Moments. Rahara Enterprises, El

Cerrito, CA, 1974.

3.Maryott, Arthur A. and Edgar R. Smith. Tables of Dielectric Constants of Pure

Liquids. National Bureau of Standards Circular No. 514, 1951.

4.Crews, Phillip, Jaime Rodriguez, and Marcel Jaspars. Organic Structure Analysis.

Oxford University Press, New York, 1998.

5. The CRC Handbook. 1998-1999. CRC Press, New York, 1998.

6. Wickelder et al. Accurate intermolecular binding energies of 1-naphthol to benzene

and cyclohexane. Chemical Physics Letters. 264 (1997) 257-264.

57

Figure 1. 3-19-04 23°C n-octanol baseline Chi2= 8.6859X 104 PrintPeakParams() For Gaussian peaks: Peak#1: position= 3640.58+/-0.308941, area= 8371.2+/-261.445, width (fwhm)= 28.2048+/-0.790589 Peak#2: position= 3673.5+/-2.69908, area= 772.137+/-248.634, width (fwhm)= 24.3575+/-6.47686, amplitude= 29.7804, width= 14.6282

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Figure 2. 3-19-04 23°C n-octanol baseline Chi2=97642.3 PrintPeakParams() For Gaussian peaks: Peak#1: position= 3640.84+/-0.21212, area= 8190.43+/-203.76, width (fwhm)= 28.7385+/-0.595582, amplitude= 267.738, width= 17.2592

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Figure 3. 3-19-04 23°C 0.05X n-octanol in CCl4 baseline Chi2=1.96614 X 105

PrintPeakParams() For Gaussian peaks: Peak#1: position= 3638.02+/-0.18571, area= 9678.54+/-234.296, width (fwhm)= 23.66+/-0.506965, amplitude= 384.294, Width= 14.2093

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Figure 4. 3-19-04 23°C 0.05X n-octanol in CCl4 baseline Chi2=1.64318 X 105 PrintPeakParams() For Gaussian peaks: Peak#1: position= 3636.35+/-0.459337, area= 8669.12+/-405.136, width (fwhm)= 25.2143+/-0.723034, amplitude= 322.995, width= 3636.35 Peak#2: position= 3643.07+/-0.465881, area= 1228.28+/-320.145, width (fwhm)= 9.77584+/-1.44632, amplitude= 118.035, width= 5.87099

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Wavenumber (cm-1)

61

Figure 5. 3-19-04 23°C 0.05X n-octanol in CBrCl3 baseline Chi2= 1.80125 X 105 PrintPeakParams() For Gaussian peaks: Peak#1: position= 3631.36+/-0.172788, area= 11897.3+/-270.08, width (fwhm)= 26.4374+/-0.495665

4000

3000

2000

1000

0

Ampl

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37503700365036003550Wavelength,

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0

100

Res

idua

ls

currentpeak

Wavenumber (cm-1)

62

Figure 6. 3-19-04 23°C 0.05X n-octanol in CBrCl3 baseline Chi2= 1.50997 X 105 PrintPeakParams() For Gaussian peaks: Peak#1: position= 3628.82+/-0.854437, area= 9841.72+/-914.368, width (fwhm)= 29.4012+/-1.11955, amplitude= 314.466, width= 17.6572 Peak#2: position= 3635.87+/-0.658756, area= 2583.27+/-877.777, width (fwhm)= 15.6179+/-2.05474, amplitude= 155.387, width= 9.37952

4000

3000

2000

1000

0

Ampl

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37503700365036003550Wavelength,

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100

Res

idua

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currentpeak

Wavenumber (cm-1)

63

Figure 7. 3-19-04 23°C 0.05X n-octanol in 50-50 CBrCl3 CCl4 baseline Chi2-3.57509 X 105 PrintPeakParams() For Gaussian peaks: Peak#1: position= 3634.65+/-0.250509, area= 11357.4+/-363.807, width (fwhm)= 26.127+/-0.705764, amplitude= 408.374, width= 15.6909

8000

6000

4000

2000

0

Ampl

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37503700365036003550Wavelength,

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0

100

Res

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currentpeak

Wavenumber (cm-1)

64

Figure 8. 3-19-04 23°C 0.05X n-octanol in 50-50 CBrCl3 CCl4 baseline Chi2=3.29379 X 105 For Gaussian peaks: Peak#1: position= 3635.62+/-0.772725, area= 10799.7+/-793.319, width (fwhm)= 23.847+/-1.34315, amplitude= 425.446, width= 14.3216 Peak#2: position= 3613.54+/-4.00886, area= 1414.52+/-785.227, width (fwhm)= 19.8015+/-6.60799, amplitude= 425.446, width=14.3216

65

4000

3000

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37503700365036003550Wavelength,

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100R

esid

uals

currentpeak

Figure 9. 3-19-04 23°C 0.05X n-octanol in 0.0994X CBrCl3 in CCl4 Baseline Chi2= 9.70348 X 104 PrintPeakParams() For Gaussian peaks:

Wavenumber (cm-1)

66

Peak#1: position= 3637.58+/-0.131519, area= 9696.28+/-166.259, width (fwhm)= 23.7786+/-0.359734, amplitude= 383.077, width= 14.2805.

2500

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37503700365036003550Wavelength,

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currentpeak

Figure 10. 3-19-04 23°C 0.05X n-octanol in 0.0994X CBrCl3 in CCl4 Baseline Chi2= 7.39625 X 104 For Gaussian peaks:

Wavenumber (cm-1)

67

Peak#1: position= 3642.1+/-0.4078, area= 1386.63+/-321.849, width (fwhm)= 11.4725+/-1.29208, amplitude= 113.545, width=6.88994 Peak#2: position= 3635.94+/-0.381281, area= 8563.72+/-357.145, width (fwhm)= 25.6708+/-0.573829, amplitude= 313.394, width= 15.4169

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500

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37503700365036003550Wavelength,

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currentpeak

Figure 11. 3-19-04 23°C 0.05X n-octanol in 0.0373X CBrCl3 in CCl4 baseline Chi2= 8.3152.3 X 104 For Gaussian peaks:

Wavenumber (cm-1)

68

Peak#1: position= 3636.43+/-0.34727, area= 8385.41+/-318.317, width (fwhm)= 25.2387+/-0.583919, amplitude= 312.122, width= 15.1574 Peak#2: position= 3642.18+/-0.419856, area= 1148.72+/-279.24, width (fwhm)= 10.4653+/-1.32728, amplitude= 103.118, width= 6.28503

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Figure 12. 3-19-04 23°C 0.05X n-octanol in 0.0373X CBrCl3 in CCl4 baseline Chi2= 1.04120 X 105 For Gaussian peaks:

Wavenumber (cm-1)

69

Peak#1: position= 3637.83+/-0.138752, area= 9301.95+/-169.24, width (fwhm)= 23.4332+/-0.37826, amplitude= 372.916, width= 14.0731

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currentpeak

Figure 13. 3-19-04 23°C 0.05X n-octanol in benzene baseline Chi2= 1.29130 X 105

PrintPeakParams()

Wavenumber (cm-1)

70

For Gaussian peaks: Peak#1: position= 3614.9+/-0.195723, area= 18913.8+/-750.526, width (fwhm)= 40.2304+/-0.858092, amplitude= 441.663, width= 24.1608 Peak#2: position= 3716.56+/-0.250623, area= 4076.8+/-199.968, width (fwhm)= 18.4702+/-0.725807, amplitude= 207.356, width= 11.0925

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Figure 14. 3-19-04 23°C 0.05X n-octanol in benzene baseline Chi2=1.18260 X 105 For Gaussian peaks:

Wavenumber (cm-1)

71

Peak#1: position= 3613.76+/-0.469352, area= 16371.5+/-955.406, width (fwhm)= 36.8848+/-1.33756, amplitude= 416.973, width= 22.1516 Peak#2: position= 3716.6+/-0.23914, area= 4226.02+/-196.665, width (fwhm)= 18.7825+/-0.6953, amplitude= 211.371, width= 11.2801 Peak#3: position= 3632.22+/-0.709424, area= 808.141+/-338.208, width (fwhm)= 12.4477+/-2.83825, amplitude= 60.9909, width= 7.47562

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Figure 15. 3-19-04 23°C 0.05X n-octanol in cyclohexane baseline Chi2= 5.52709 X 104 For Gaussian peaks:

Wavenumber (cm-1)

72

Peak#1: position= 3642.61+/-0.173144, area= 4482+/-117.186, width (fwhm)= 20.2831+/-0.470792, amplitude=207.589, width= 12.1813 Peak#2: position= 3710.25+/-0.216644, area= 6423.08+/-208.185, width (fwhm)= 28.3947+/-0.671446, amplitude= 212.507, width= 17.0528

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Figure 16. 3-19-04 23°C 0.05X n-octanol in cyclohexane baseline Chi2=4.69421 X 104 For Gaussian peaks:

Wavenumber (cm-1)

73

Peak#1: position= 3647.5+/-1.19059, area= 1989.18+/-804.888, width (fwhm)= 12.3963+/-1.29679 , amplitude= 150.748, width= 7.44474 Peak#2: position= 3710.38+/-0.198585, area= 6122.47+/-178.032, width (fwhm)= 27.6088+/-0.600886, amplitude= 208.328, width= 16.5808 Peak#3: position= 3637.08+/-2.39184, area= 2308.92+/-813.491, width (fwhm)= 15.8672+/-2.67121, amplitude= 136.703, width= 9.5292

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Figure 17. Solvent n-octanol

C BrCl3

0.0475X CBrCl3 in CCl4

0.0994X CBrCl3 in CCl4

0.0373X CBrCl3 in CCl4 C Cl4

Benzene

Wavenumber (cm-1)

74

Cyclohexane Position of Free OH Peak 3640.84 +/-0.21212 3631.36 +/-0.172788 3634.65 +/- 0.250509 3637.58 +/- 0.131519 3637.83 +/- 0.138752 3638.02 +/- 0.18571 3614.9 +/- 0.195723

3642.61 +/- 0.173144 Area of Free OH Peak 8190.43 +/-203.76 11897.3 +/-270.08 11357.4 +/- 363.807 9696.28 +/-166.259 9301.95 +/-169.24 8669.12 +/- 405.136 18913.8 +/- 750.526 4482 +/-117.186

Polarizability (Å3) 11.25 Parallel to ring6 12.3 Perpendicular to ring6 6.64 Parallel to ring6 11.8 Perpendicular to ring6 10.1

Dipole Moment11,2,3 ~1.7 in Benzene, in CCl4, liquid 0.21 (pure liquid) 0.1 (pure

liquid) 0 (pure liquid) 0 (pure liquid)

Quadropole Moment6 ____________ ____________ ____________ ____________ ____________ ____________ -(29.0 +/- 1.7) X 10-40 Cm2

(3.0 +/- 1.7) X 10-40 C m2

75

Figure 18. A graph of the position of the free OH peak of 0.050X n-octanol versus mole fraction of CBrCl3 in CCl4. (Three components solution.)

y = -6.7961x + 3638.1R2 = 0.9976

3630

3631

3632

3633

3634

3635

3636

3637

3638

3639

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Mole Fraction of CBrCl3 in CCl4

Posi

tion

of F

ree

OH

Pea

k (c

m-1

)

76

Figure 19. A graph of the area of the free OH peak of 0.050X n-octanol (as determined with Igor and assuming only one component) versus mole fraction of CBrCl3 in solvent.

y = 2597.3x + 9549.1R2 = 0.8997

0

2000

4000

6000

8000

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12000

14000

0 0.2 0.4 0.6 0.8 1 1.2

Mole Fraction CBrCl3 in CCl4

Are

a

77

Figure 20: A graph of the area of the free OH components of 0.050X n-octanol (as determined with Igor and assuming two components) versus mole fraction of CBrCl3 in solvent.

y = 1395.3x + 1190.2R2 = 0.99

y = 1349.6x + 8481.5R2 = 0.9547

0

2000

4000

6000

8000

10000

12000

0 0.2 0.4 0.6 0.8 1 1.2

Mole Fraction of CBrCl3 (X)

Are

a of

Com

pone

nt

Low-Energy Comp High-energy comp Linear (High-energy comp) Linear (Low-Energy Comp)

78

Figure 21: A graph of the positions of the two free OH components of 0.050X n-octanol versus mole fraction of CBrCl3 in CCl4.

y = -7.7503x + 3636.6R2 = 0.9978

y = -6.9088x + 3642.8R2 = 0.9939

3626

3628

3630

3632

3634

3636

3638

3640

3642

3644

3646

0 0.2 0.4 0.6 0.8 1 1.2

Mole Fraction of CBrCl3 (X)

Posi

tion

of fr

ee O

H p

eak

(cm

-1)

low energy comp high evergy comp Linear (low energy comp) Linear (high evergy comp)

79

Figure 22. A plot of the CH stretching region of 0.050X n-octanol solutions in organic halogen solvents, and those solvents. (*= Pure Solvent) 23ºC.

2856.6707912864.004441

2902.003957

2877.183805

2962.189022

2936.879659

0

1000

2000

3000

4000

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6000

2700 2750 2800 2850 2900 2950 3000 3050 3100 3150

Wavenumbers (cm-1)

Inte

nsity

(a.u

.)

noctstart/5.5 noctend/5.5 in CCl4

in CBrCl3 CBrCl3* in 0.475 CBrCl3

in 0.0994X CBrCl3 0.0994X CBrCl3* in 0.0373X CBrCl3

80

Figure 23. A fit of the peaks for the CH stretching region by Igor of pure n-octanol scaled down by 20 to have areas and amplitudes more equivalent to 0.050X n-octanol, the baseline of the spectra is taken into account. 23ºC. Chi2= 1.02584X 105 For Gaussian peaks: Peak#1: position= 2854.13+/-0.0992234, area= 11564.4+/-864.369, width (fwhm)= 14.6678+/-0.345775 Peak#2: position= 2868.96+/-0.842089, area= 13798.6+/-1275.28, width (fwhm)= 27.221+/-1.46855 Peak#3: position= 2939.04+/-0.121998, area= 3850.89+/-193.63, width (fwhm)= 13.7884+/-0.430315 Peak#4: position= 2902.88+/-0.303286, area= 112428+/-1195.77, width (fwhm)= 78.8571+/-0.585064 Peak#5: position= 2965.99+/-0.185224, area= 3692.92+/-184.547, width (fwhm)= 17.1646+/-0.559587

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Wavenumber (cm-1)

81

Figure 24. A fit of the peaks for the CH stretching region by Igor of 0.050X n-octanol in CCl4, with 0.950 X a CCl4 spectrum subtracted out. The baseline of the spectra is taken into account by the program. 23ºC. Chi2= 4.30966 X 105 For Gaussian peaks: Peak#1: position= 2856.56+/-0.0960393, area= 29529.5+/-554.671, width (fwhm)= 17.1791+/-0.232361, amplitude= 1614.82, width= 10.3171 Peak#2: position= 2875.28+/-0.205622, area= 11269.4+/-443.312, width (fwhm)= 15.1213+/-0.438227, amplitude= 700.129, width= 9.08126 Peak#3: position= 2903.8+/-0.224044, area= 177607+/-2271.01, width (fwhm)= 77.2147+/-0.782919, amplitude= 2160.86, width= 46.3722 Peak#4: position= 2938.93+/-0.095997, area= 9298.61+/-359.354, width (fwhm)= 13.1431+/-0.326506, amplitude= 664.641, width= 7.89326 Peak#5: position= 2966.25+/-0.222045, area= 6607.31+/-381.552, width (fwhm)= 17.5114+/-0.662673, amplitude= 354.464, width= 10.5166

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3100300029002800Wavelength,

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Res

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currentpeak

Wavenumber (cm-1)

82

Figure 24. A fit of the peaks for the CH stretching region by Igor of 0.050X n-octanol in CCl4, with 0.950 X a CBrCl3 spectrum subtracted out. The baseline of the spectra is taken into account by the program. 23ºC. Chi2 =4.80572 X 105 For Gaussian peaks: Peak#1: position= 2855.23+/-0.122927, area= 29807.7+/-669.184, width (fwhm)= 17.2248+/-0.266289, amplitude= 1625.7, width= 10.3446 Peak#2: position= 2937.58+/-0.101016, area= 9620.73+/-401.495, width (fwhm)= 13.2527+/-0.344063, amplitude=681.98, width= 7.95906 Peak#3: position= 2873.66+/-0.268331, area= 12178.9+/-573.623, width (fwhm)= 16.1135+/-0.536513, amplitude=710.044, width= 9.67716 Peak#4: position= 2903.63+/-0.234016, area= 185097+/-2556.56, width (fwhm)= 76.6143+/-0.859315, amplitude= 2269.64, width=46.0116 Peak#5: position= 2965.6+/-0.264409, area= 7434.87+/-486.274, width (fwhm)= 19.7005+/-0.783168, amplitude= 354.539, width= 11.8314

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Wavenumber (cm-1)

83

Summary of Conclusions:

1. What causes the changes in free OH peak?

Polarizability is shown to affect the position and size of the free OH peak from

looking at the free OH peaks of solutions with CCl4 and CBrCl3. They both have

approximately the same dipole, but the polarizability is different. From looking at the

peak postitions of n-octanol in CHCl3 (dipole moment +1 to 1.2) and CCl4 (dipole

moment 0), a shift in the free OH peak and the lack of hydrogen bonding evident suggest

that dipole moment of the solvent affects the OH bond. CHCl3 has less polarizability than

CCl4, so polarizability is not the cause of the red shift in this case.

2. What is the cause of the red shift in benzene?

Benzene is not more polarizable than cyclohexane. So polarizability is not the

cause of the red shift of the free OH of n-octanol in benzene. Neither is dipole moment,

as neither benzene nor cyclohexane has one. However, as discussed in the fourth chapter,

the shift may be due to orientation of the hydroxyl of n-octanol in an induced magnetic

field around n-octanol or interactions of the OH with the pi electrons in the electron cloud

of benzene. Also the presence of a large negative Quadrupole may affect the free OH of

n-octanol in benzene.

3. What causes the change in CH intensities of n-octanol when it is solvated by

halogenated organic solvents?

There looks to be a change in some intensities of the CH stretching of n-octanol

solvated in organic halogens when compared to pure n-octanol, but no obvious shift in

84

wavenumber. This is a complicated part of the spectrum, information about solvation is

easier to get from OH region, most especially the free OH peak. Information is not

availible for this region from n-octanol solvated with benzene and cyclohexane because

of peaks in mutual positions and they did not subtract out cleanly.

4. Is 0.050X n-octanol a good concentration for comparisons between the effects of

different solvents?

0.05X n-octanol free OH peak can not be compared between solvents by itself as

there may be two things affecting their area/intensity/width: the presence/absence of

hydrogen bonding, and whether a solvent is somehow amplifying the signal. I suspect

benzene at the very least, since that peak is larger than for chloroform which appears, as

evidenced by the linear relationship between all studied concentrations and signal from

the free OH peak, to participate in no detectable n-octanol-- n-octanol hydrogen bonding.

5. Does the free OH peak have two components?

It appears that in cyclohexane, CBrCl3, and CCl4 there are two components to the

free OH peak. It is possible that n-octanol does fit as easily with two components in the

50-50 CBrCl3-CCl4 solvent because they are too close together and one may be very

small in comparison to the other making it difficult to determine.

85

Future work:

1. Many more points on the graphs of area of free OH peak versus concentration must be

made to 1. Reproduce the data. 2. Determine the slope of the linear part of the line before

H-bonding starts to see if more polarizable compounds are somehow enhancing the free

OH signal. 3. Determine at what concentration in a solvent hydrogen bonding starts from

where the graphs begin to curve down.

2. A wider variety of different CBrCl3/CCl4 concentrations solvating 0.050X n-octanol

must be examined to determine if the solvent behaves as a uniform solution with regards

to polarizability.

3. The nature of solvation of n-octanol by benzene should be determined. Perhaps this

may be achieved by looking at n-octanol in low concentrations of benzene in

cyclohexane or carbon tetrachloride. If there are enough n-octanols, they can’t all interact

with the same part of benzene. This would show if the shift is due to orientation of n-

octanol around benzene.

4. Maybe someday someone else can figure out what causes the change in intensity for

the CH region. (The article by Badger et al. cited previously would be a good start.)

5.It would seem a reasonable aim to develop models to approximate the effects of the

different solvents on alcohols.

86