infra red spectroscopy (plus worksheet answers)

7/28/2019 Infra Red Spectroscopy (Plus Worksheet Answers)

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IR SPECTROSCOPY


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Light is one form of electromagnetic radiation. Light is only a very small part of the electromagnetic spectrum. Electromagnetic waves consist of electric and magnetic fields

which are perpendicular to each other and to the direction of travel of the wave.

The electric and magnetic fields vibrate at the same frequency

as each other.


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THE ELECTROMAGNETIC SPECTRUM


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Atoms, molecules and ions can absorb (or emit)electromagnetic radiation of specific frequencies, and this

can be used to identify them.

Electromagneticradiation absorbed

What the energy isused for

Spectroscopytechnique

Ultra-violet / visible Movement of electrons tohigher energy levels

Ultra-violet / visiblespectroscopy

Infra-red To vibrate bondsInfra-red

spectroscopy

Microwaves To rotate molecules Microwavespectroscopy

Radio waves To change nuclear spin NMR spectroscopy


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INFRA-RED SPECTROSCOPY

All bonds vibrate at a characteristic frequency. There are different types of vibration.

Symmetric stretch Assymmetric stretch Bending

The frequency depends on the mass of the atoms in the bond,

the bond strength, and the type of vibration. The frequencies at which they vibrate are in the infra-red region

of the electromagnetic spectrum.


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INFRA-RED SPECTROSCOPY

Wavenumbers (cm -1) are used as a measure of the wavelengthor frequency of the absorption.

Wavenumber = 1wavelength (cm)

If IR light is passed through the compound, it will absorb someor all of the light at the frequencies at which its bonds vibrate.

IR light absorbed is in the range 4000 400 cm -1.

Above 1500 cm -1 is used to identify functional groups.

Below 1500 cm -1 is used for fingerprinting.


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BELOW 1500 cm -1 Fingerprinting

Complicated and contains many signals picking outfunctional group signals difficult.

This part of the spectrum is unique for every compound, andso can be used as a "fingerprint".

This region can also be used to check if a compound is pure.


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CH2 C

CH3

CH2 CH3

CH3 C CH

CH3

CH3


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cyclohexane

C H


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cyclohexene

C H


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butanal

C H

CH2 CH2 C

O

HCH3


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ethanoic acid

O H

CH3 C

O

O H


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propan-1-ol

O H

CH 3 CH 2 CH 2 OH


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butanal

C=O

CH2 CH2 C

O

HCH3


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propanone

C=O

CH3 C

O

CH3


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ethanoic acid

C=O

CH3 C

O

O H


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methyl ethanoate

C=O

CH3 C

O

O CH 3


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10

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% T

5001000150020002500300035004000

Wavenumbers (cm-1)

hex-1-ene

C=C


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2-methylbut-2-ene

C=C


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Exercise 1

Match the following eight compounds to thefollowing eight IR spectra.

hex-2-ene

pentane

methylpropan-1-ol

2-methylpentan-3-one

butanal

butanoic acid

propyl ethanoate

nitrobenzene


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10

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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)


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5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)


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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)


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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)


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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)


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5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)


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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)


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10

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5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)


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C-O

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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)

C=O

propyl ethanoate CH3 CO

O CH 2 CH2 CH3


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C=O

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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)

2-methylpentan-3-one CH3 CH CO

CH2 CH3

CH3


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methylpropan-1-ol

O-H

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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)

CH3 CH CH 2 OH

CH3


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C-H

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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)

nitrobenzene NO2


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C-H

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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)

pentane CH3 CH2 CH2 CH2 CH3


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C-H 10

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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)

C=O

butanal CH3 CH2 CH2 CO

H


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O-H

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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)

butanoic acid CH3 CH2 CH2 CO

O H


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C=C

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% T

5001000150020 0025 003000350 0400 0

Wavenumbers (cm-1)

C-H C-H

hex-2-ene CH3 CH CH CH 2 CH2 CH3


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% T

5001000150020002500300035004000

Wavenumbers (cm-1)


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5001000150020002500300035004000

Wavenumbers (cm-1)


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11

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5001000150020002500300035004000

Wavenumbers (cm-1)


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5001000150020002500300035004000

Wavenumbers (cm-1)

F


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G

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% T

5001000150020002500300035004000

Wavenumbers (cm-1)


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P


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Q


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R


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S


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T


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U

infra red spectroscopy (plus worksheet answers)

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