Question

Interpret the IR spectra for an unknown liquid substance. Label all major bond types, and identify the unknown substance.

The substance may be:

Acetone

Benzaldehyde

Diethyl Ether

Ethyl Acetate

Methanol

Methyl Benzoate

Toluene

1% "48000 3500 3000 2500 2000 1500 1000 600 cm-1

Answer 1

The given spectrum is for acetone and peak assignment has been shown below. C-H stretching 1% H3C-CH3 C=O stretching CH, group, bending - C-C-C stretching 4000 3500 3000 2500 cm-1 2000 1500 1000 600 Note: The spectrum is not for other compounds because of following reasons: (a) Cannot be for Benzaldehyde, Methyl Benzoate and Toluene: the peaks for aromatic C-H stretching @ around 3030 cm-1 and aromatic C- C skeletal vibrations @ around 1600 cm-1 are absent. That means no aromatic moiety. (b) Cannot be Methanol: The strong and broad peak for O-H stretching @ around 3300 to 3600 cm-1 and C-O stretching around 1035 cm-1 are absent. That means no OH group. (c) Cannot be Diethyl Ether and Ethyl Acetate: The strong peak for C-O stretching @ around 1035 cm-1 is absent. That means no C-O bond.