An introduction to UV-IR spectroscopy

An Introduction toAn Introduction to

UV – IRUV – IRSpectroscopySpectroscopy

By : Daruosh ShafieeBy : Daruosh Shafiee

Different areas of Different areas of Electromagnetic spectrumElectromagnetic spectrum

Spectrum X: breaking the linkSpectrum X: breaking the link

Spectrum UV: electron transferSpectrum UV: electron transfer

Spectrum IR: vibrationsSpectrum IR: vibrations

Spectrum MW: rotational movementsSpectrum MW: rotational movements

Spectrum RF: nuclear spinSpectrum RF: nuclear spin

IR SpectrophotometryIR Spectrophotometry

Almost all covalently bonded compounds are absorbed Almost all covalently bonded compounds are absorbed in thein the

IR region. IR region has a wavelength longer than the IR region. IR region has a wavelength longer than the wavelength of visible light (VIS) and shorter than wavelength of visible light (VIS) and shorter than microwaves (MW) is. The most important part of the microwaves (MW) is. The most important part of the spectrum to study the behavior of chemicals in the spectrum to study the behavior of chemicals in the range of 660 cm-1 4000, respectively.range of 660 cm-1 4000, respectively.

E = h.E = h. = h.C/ = h.C/E E 1/ 1/

In the process of absorbing IR In the process of absorbing IR frequencies of molecular vibrations with frequencies of molecular vibrations with frequencies match is absorbed and the frequencies match is absorbed and the absorbed energy is used to increase the absorbed energy is used to increase the range of motion of molecular vibrations.range of motion of molecular vibrations.

Point :Point : Only bonds with a dipole moment (the Only bonds with a dipole moment (the

asymmetry in the bond) can absorb IR radiation asymmetry in the bond) can absorb IR radiation and symmetrical, such as H-H bonds do not and symmetrical, such as H-H bonds do not absorb IR radiation.absorb IR radiation.

IR AbsorptionIR Absorption

The application of IR SpectrumThe application of IR Spectrum

1- Each frequency (energy) has its own vibration and a 1- Each frequency (energy) has its own vibration and a bond in two molecules is in two different bond in two molecules is in two different environments with different structures, so they environments with different structures, so they never have same IR spectrum. The IR spectrum can never have same IR spectrum. The IR spectrum can be used like fingerprints for molecular identification. be used like fingerprints for molecular identification. By comparing the IR spectra of the two materials can By comparing the IR spectra of the two materials can be figured out whether they are one or not?be figured out whether they are one or not?

2- IR spectrum also gives us information about the 2- IR spectrum also gives us information about the structure of the molecule. For example, the structure of the molecule. For example, the existence of such functional groups such as Cexistence of such functional groups such as CC, C, CCN, C=O, O-H, N-H and conversion of the index in N, C=O, O-H, N-H and conversion of the index in certain areas of the IR spectrum that represents the certain areas of the IR spectrum that represents the will of the linkages in the molecule.will of the linkages in the molecule.

The stronger bond be required higher frequency The stronger bond be required higher frequency

(energy) to its vibration:(energy) to its vibration:

CCC > C=C > C-CC > C=C > C-C21502150 cmcm-1-1 1650 cm 1650 cm-1-1 1200 cm 1200 cm-1-1

IR absorption of various bondsIR absorption of various bonds

As the mass of the atoms attached to the carbon As the mass of the atoms attached to the carbon increases the frequency (energy) to reduce increases the frequency (energy) to reduce vibration link:vibration link:

C-H > C-C > C-O > C-Cl > C-BrC-H > C-C > C-O > C-Cl > C-Br3000cm3000cm-1-1 1200cm 1200cm-1-1 1100cm 1100cm-1-1 800cm 800cm-1-1 600cm 600cm-1-1

Concerns the interpretation of peaks IR:Concerns the interpretation of peaks IR: IR spectroscopy is a technique for detection of IR spectroscopy is a technique for detection of

functional groups. Important functional groups functional groups. Important functional groups that routinely combined for evaluation include:that routinely combined for evaluation include:

C=O C=O ، ، O-H O-H ، ، N-H N-H ،،C=C C=C ، ، CCC C ، ، CCNN وو... ...

IR InterpretationIR Interpretation

To interpret IR peaks the following steps should be To interpret IR peaks the following steps should be considered:considered:

1. Is the carbonyl group (C = O) exist?1. Is the carbonyl group (C = O) exist?There is a strong absorption in the There is a strong absorption in the 1700 - 1800 1700 - 1800 cm-1 cm-1 in the form of a strong peakin the form of a strong peak..

2. If the carbonyl group (C=O) exists, the 2. If the carbonyl group (C=O) exists, the following processes must be considered. following processes must be considered. If not go to step 3.If not go to step 3.

- -Acids: Are there groups O-H? (R-CO-Acids: Are there groups O-H? (R-CO-OH)OH) There is a very strong and broad There is a very strong and broad

absorption in the 2500 - 3400 cm-1absorption in the 2500 - 3400 cm-1

Amides: Does the group N-H there? (R-CO-Amides: Does the group N-H there? (R-CO-NH2)NH2)

There are moderate absorptions near There are moderate absorptions near 3500 cm-13500 cm-1

Esters: Does the group C-O there? (R-CO-Esters: Does the group C-O there? (R-CO-OR)OR)

There are strong appeal in the There are strong appeal in the 1000-1300 cm-11000-1300 cm-1

Aldehydes: Is aldehyde C-H groups are Aldehydes: Is aldehyde C-H groups are there? (RH-CO-H)there? (RH-CO-H)Two weak absorption in the 2700 - 2800 cm-1 Two weak absorption in the 2700 - 2800 cm-1

to C-H absorption ordinaryto C-H absorption ordinary

- Ketones: (R-CO-R)- Ketones: (R-CO-R)If none of the above conditions is not If none of the above conditions is not

available.available.

3. If the carbonyl group (C=O) did not exist:3. If the carbonyl group (C=O) did not exist:

Alcohol (phenols): Alcohol (phenols): Does the group O-H there? (R-OH)Does the group O-H there? (R-OH)There is strong & broad absorption in the 3200-3500 There is strong & broad absorption in the 3200-3500 cm-1cm-1

Amines: Does the group N-H there? (R-Amines: Does the group N-H there? (R-NH2)NH2)

There are moderate absorption near 3400cm-1There are moderate absorption near 3400cm-1

Ethers: Does the group C-O there? (R-Ethers: Does the group C-O there? (R-A-R)A-R)

There are strong attractions in area 1000-1300 There are strong attractions in area 1000-1300 cm-1cm-1

4- Double bonds or aromatic: Is there Group 4- Double bonds or aromatic: Is there Group C=C?C=C?

- Poor absorption in the 1650 cm-1 is indicative of - Poor absorption in the 1650 cm-1 is indicative of C=CC=C

- Moderate or high conversions of 1400-1650 cm-1 - Moderate or high conversions of 1400-1650 cm-1 and usually crowded area and the absorbance and usually crowded area and the absorbance at 650-800 cm-1 represents the aromatic.at 650-800 cm-1 represents the aromatic.

. .

5. The triple bonds C5. The triple bonds CC or CC or CN ? N ? - Medium and sharp absorption about 2250 - Medium and sharp absorption about 2250 cm-1 indicates cm-1 indicates CCNN- Medium and sharp absorption about 2150 - Medium and sharp absorption about 2150 cm-1 indicates cm-1 indicates CCCC

66- Hydrocarbons: (R-H)- Hydrocarbons: (R-H)- There is none of the above attractions- There is none of the above attractions..

UV SpectroscopyUV Spectroscopy

The frequency (Energy) of UV is in the range of The frequency (Energy) of UV is in the range of electronic transitions. The atoms or electronic transitions. The atoms or molecules can absorb UV radiation and then molecules can absorb UV radiation and then the electron can stimulate from one basic the electron can stimulate from one basic electronic level to higher levels, and it is the electronic level to higher levels, and it is the base of UV spectroscopy. base of UV spectroscopy.

The principle of Absorption The principle of Absorption SpectroscopySpectroscopy

Beer-Lambet LawBeer-Lambet Law::Direct relation between Absorption versusDirect relation between Absorption versus

Concentration in Quantitative analysisConcentration in Quantitative analysis

Absorption coefficient (Absorption coefficient () has the range of 0 to 1,000,000) has the range of 0 to 1,000,000>>10,00010,000) ) strong attractionstrong attraction ( (and >1,000 (weak absorption)and >1,000 (weak absorption)

Beer-Lambert limitationsBeer-Lambert limitations

1. Instrumental deviations1. Instrumental deviations1.1. beam of light (1.1. beam of light (max)max) The absorption coefficient (The absorption coefficient () depends on the wavelength. ) depends on the wavelength. 1.2. Stray radiations (side lights)1.2. Stray radiations (side lights) Absorbance linearity with respect to the concentration Absorbance linearity with respect to the concentration

overshadowed.overshadowed.

2. Chemical Deviations 2. Chemical Deviations 2.1. Beer-Lambert law holds true in low concentrations.2.1. Beer-Lambert law holds true in low concentrations.2.2. Interaction between molecules increased in higher 2.2. Interaction between molecules increased in higher

concentrations and density affect them. In fact, the concentrations and density affect them. In fact, the interaction of molecules to affect their ability to interaction of molecules to affect their ability to attract and cause the linearity calibration.attract and cause the linearity calibration.

2.3. In high concentrations cause many changes in the 2.3. In high concentrations cause many changes in the refractive index solution to the absorbed dose refractive index solution to the absorbed dose linearity.linearity.

2.4. Deviation from the separation or reactive chemical 2.4. Deviation from the separation or reactive chemical species, absorbing unwantedspecies, absorbing unwanted

Overview of SpectrophotometerOverview of Spectrophotometer

Some terms in UV spectrumSome terms in UV spectrum

ChromophoresChromophoresSpecific functional groups (unsaturated) that are Specific functional groups (unsaturated) that are

responsible for absorbing the molecules. Such as responsible for absorbing the molecules. Such as C=C, C=O, NO2 and ...C=C, C=O, NO2 and ...

Oxochromes:Oxochromes:Saturation groups (substituted) that if connected to Saturation groups (substituted) that if connected to

numerous chromophores can change the numerous chromophores can change the wavelength and intensity of UV absorption. Such wavelength and intensity of UV absorption. Such as NH2, OH and ...as NH2, OH and ...

Bathochromic displacement (red Bathochromic displacement (red displacement)displacement)

The absorption spectrum towards longer The absorption spectrum towards longer wavelengths transfer or substitution of solventwavelengths transfer or substitution of solvent

Hypsochromic or blue shift Hypsochromic or blue shift Transfer to the absorption spectrum of wavelengths Transfer to the absorption spectrum of wavelengths

shorter or substitution of solventshorter or substitution of solvent

Solvents should be "Solvents should be "Solvents for Solvents for spectroscopyspectroscopy" because the impurities do not " because the impurities do not disturb the UV spectrum (Solvents no effect disturb the UV spectrum (Solvents no effect on UV). Purity suitable solvent and solute to on UV). Purity suitable solvent and solute to be ineffective.be ineffective.

CompoundCompound maxmax maxmaxBenzeneBenzene 256256 200200TolueneToluene 261261 300300m, Xylenem, Xylene 263263 3003001,3,5- Trimethyl 1,3,5- Trimethyl BenzeneBenzene 266266 300300Hexa methyl BenzeneHexa methyl Benzene 272272 300300

In multi-core aromatic compounds toward In multi-core aromatic compounds toward longer wavelengths absorbed by increasing longer wavelengths absorbed by increasing the number of rings (Bathochromic shift) is the number of rings (Bathochromic shift) is shifted to the visible region.shifted to the visible region.