CHM 232: Common Infrared Absorption Frequencies

Alcohol

3200-3600 cm^-1

Carboxylic Acid

2500-3600 cm^-1

N-H

3350-3500 cm^-1

sp C-H

3310-3320 cm^-1

sp2 C-H

3000-3100 cm^-1

sp3 C-H

2850-2950 cm^-1

sp2 C-O

1200 cm^-1

sp3 C-O

1025-1200 cm^-1

Double Bonds e.g. C=C, C=O

1620-1680 cm^-1

Aldehydes and Ketones

1710-1750 cm^-1

Carboxylic acids (double bonds)

1700-1725 cm^-1

Acid anhydrides

1800-1850 and 1740-1790 cm^-1

Acyl halides

1770-1815 cm^-1

Esters

1730-1750 cm^-1

Amides

1680-1700 cm^-1

C≡C

2100-2200 cm^-1

C≡N

2240-2280 cm^-1

What are alkenes?

hydrocarbons with double bonds

RCH=CH2

910,990 cm^-1

R2C=CH2

890 cm^-1

cis-RCH=CHR'

665-730 cm^-1

trans-RCH=CHR'

960-980 cm^-1

R2C=CHR'

790-840 cm^-1

Substituted derivatives of benzene: Monosubstituted

730-770 and 690-710 cm^-1

Substituted derivatives of benzene: Ortho-disubstituted

735-770 cm^-1

Substituted derivatives of benzene: Meta-disubstituted

750-810 and 680-730 cm^-1

Substituted derivatives of benzene: Para-disubstituted

790-840 cm^-1

Higher bond strength...

Higher frequency

Higher mass...

Lower frequency

Wavenumber

cm^-1

Reciprocal of the wavelength measured in centimeters (cm); directly proportional to frequency

Used to measure frequency

Higher wavenumber = higher frequency = higher energy vibration

What is Spectroscopy?

Study of the interaction of electromagnetic radiation with matter; typically involves the absorption of electromagnetic radiation

What is Spectrometry?

Evaluation of molecular identity and/or properties that does not involve interaction with electromagnetic radiation

What is Infrared Spectroscopy?

IR spectroscopy is used to determine the functional groups in a substance

Measures the stretching and bending frequencies of covalent bonds that contain a dipole moment

What is Nuclear Magnetic Resonance (NMR) Spectroscopy?

Used to determine the connectivity (C,H framework) of a molecule

Measures the energy associated with spin states of nuclei in the presence of a magnetic field