LSW F02 Organic Chemistry Exam II notes Spectroscopycms.cerritos.edu/uploads/lwaldman/211Lecture/Notes/... · LSW F02 Organic Chemistry Exam II notes Spectroscopy Empirical Formula:

LSW F02 Organic Chemistry Exam II notes

Spectroscopy

Empirical Formula: Chemical Formula: Index of Hydrogen Deficiency (IHD)

A)From a structure: B)From a molecular formula, CcHhNnOoXx,

Formula for saturated hydrocarbons:

Subtract the number of hydrogens the compound has:

Subtract the number of halogens the compound has:

The Oxygen is ignored:

For Nitrogen add one H:

Multiply by 0.5:

What is the IHD of the following molecular formulas?

C6H10 C6H6 C4H8O C4H9N C2Cl2

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Electromagnetic Radiation (EMR):

Wave-like properties:

Particle-like properties:

Energy States: Quantization of Energy:


Infra red (IR) spectroscopy Vibrations of covalent bonds within a molecule Vibrations:

IR region spectrum

Two regions:

• 4000-1000 cm-1 known as the functional group region, and

• < 1000 cm-1 known as the fingerprint region

• functional group region:

• fingerprint region:

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Hookes' Law

1. stronger bond (larger k value), υ increases.

increasing bond strength compare: C-C C=C C≡C C-C-H C=C-H C≡C-H

2. heavier atoms attached (larger m value), υ decreases.

increasing reduced mass:

C-H

C-C

C-Cl

C-Br

C-I

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Bond Base Value

Strength / Shape Comments

1 C=O 1715 s, "finger"

2 O-H 3600 s, brd

3 N-H 3500 m

4 C-O 1100 s

5 C=C 1650 w alkene

aromatic

m-s

6 C≡C 2150 w, sharp

7 C-H 3000 s

8 C≡N 2250 m, sharp

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Sample IR Spectra: toluene

Acetone (2-propanone)

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2-propanol:

Butanoic acid

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Methyl acetate or methyl ethanoate:

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Nuclear Magnetic Resonance (NMR): 1H NMR or proton NMR or PMR or just NMR 13C NMR or CMR

Only certain molecules can show absorbance in NMR

What is happening:

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Chemical Shift • NMR spectrum:

• Resonance:

• Chemical shift:

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Calculate the chemical shift of a peak that occurs 655.2 Hz downfield of TMS on a spectrum recorded using a 90 MHz spectrometer ? Calculate the frequency of the chemical shift of chloroform (CHCl3, δ=7.28 ppm) relative to TMS on a spectrum recorded on a 300 MHz spectrometer? Shielding in 1H-NMR

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Factors which affect chemical shift: Electronegativity:

Compound,

CH3X X Electro-

negativity of X

Chemical shift

δ / ppm CH3F F 4.0 4.26 CH3OH O 3.5 3.4 CH3Cl Cl 3.1 3.05 CH3Br Br 2.8 2.68 CH3I I 2.5 2.16 CH4 H 2.1 0.23 (CH3)4Si Si 1.8 0 Cumulative

effect

CH2Cl2 5.30 CHCl3 7.27 Distance

effect

CH2- CH2- CH2Br

1.25 1.69 3.30

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Magnetic Anisotropy

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Hydrogen Bonding

D2O (deuterium oxide) exchange experiment.

1H-NMR Chemical shifts

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I

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Coupling in 1H-NMR

CH3 with CH next door

H

Cl

Cl

H

H H

H

Cl

Cl

H

H H

Ho

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CH with CH3 next door

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1,1-dichloroethane: • δ = 5.9 ppm

• δ = 2.1 ppm

Coupling Constant, J

Pascal's Triangle

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Predicting Spectra Predict the spectrum for propane including multiplicity and the relative intensities in propane (CH3CH2CH3). How many different types of hydrogen?

What is the chemical shift?

What is the integration?

What is the multiplicity?

What are the intensities?

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Complex Coupling Patterns

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Interpreting 1H-NMR Spectra How many types of H? how many groups of signals in the spectraWhat types of H? chemical shift of each group How many H of each type are there? integration (relative area) for each group. What is the connectivity? coupling patterns.

Integration Coupling

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Peak Chemical

Shift (δ) ppm

Integration Equivalent Hydrogens

Multiplicity Neighboring Hydrogens

Possible Group

circle the H A

B

C

D

E

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LSW F02 Organic Chemistry Exam II notes Spectroscopycms.cerritos.edu/uploads/lwaldman/211Lecture/Notes/... · LSW F02 Organic Chemistry Exam II notes Spectroscopy Empirical Formula: