IR Spectroscopy

The functional group region

(4000–1400 cm–1)

The functional group (diagnostic region) -- determines the functional group present

The fingerprint region

1400–600 cm–1)

The fingerprint region -- used for structure elucidation by spectral comparison.

Wavenumber is

proportional to frequency (ν)

• Wavenumber is inversely proportional to wavelength (λ)

100 % transmittance =

all light shone is transmitted, none absorbed

0 % transmittance

None of the light shone is transmitted, all is absorbed

•IR Spectroscopy

primarily used to detect Functional Groups present.

IR Absorptions

arise due to stretching and bending of covalent bonds in molecules

Infrared Spectroscopy

IR Absorptions – Four regions of the IR spectrum

amines

N-H stretching    ~3300 cm-1  broad
        1o = doublet, 2o = singlet, 3o = none
  C-N stretching  ~1000-1250 cm-1

ketones

C=O stretching  ~1715 cm-1

aldehydes

C=O stretching  ~1725 cm-1

carboxylic acid

C=O stretching  ~1700 cm-1
  O-H stretching  ~3000-2500 cm-1  broad

esters

C=O stretching  ~1735 cm-1

amides

C=O stretching  ~1690 cm-1

acid chloride

C=O stretching  ~1800 cm-1

anhydride

C=O stretching  ~1820 & 1760 cm-1

Anhydride C=O stretching

~ 1840 & 1760 cm-1

2 peaks