Question

Infrared Spectroscopy may be used to identify certain functional groups in organic molecules. Two of the most important are -OH stretch vibrations and C=O stretch vibrations. Match each of the functional groups below to the appropriate wavenumber range for absorption bands in IR spectra.

C=O stretch modes	Answer 1 Choose... 2850-3000 cm-1 / 1600-1800 cm-1 / 3040-3140 cm-1 / 1070-1150 cm-1 / 3000-3500 cm-1
-CH stretch modes in alkenes	Answer 2 Choose... 2850-3000 cm-1 / 1600-1800 cm-1 / 3040-3140 cm-1 / 1070-1150 cm-1 / 3000-3500 cm-1
-CH stretch modes in alkanes	Answer 3 Choose... 2850-3000 cm-1 / 1600-1800 cm-1 / 3040-3140 cm-1 / 1070-1150 cm-1 / 3000-3500 cm-1
-OH stretch modes	Answer 4 Choose... 2850-3000 cm-1 / 1600-1800 cm-1 / 3040-3140 cm-1 / 1070-1150 cm-1 / 3000-3500 cm-1
ethereal C-O-C stretch modes	Answer 5 Choose... 2850-3000 cm-1 / 1600-1800 cm-1 / 3040-3140 cm-1 / 1070-1150 cm-1 / 3000-3500 cm-1

Answer 1

C=O stretch mode appears in 1600 - 1800 cm-1 region in IR spectra.

-CH stretch modes in alkenes appear in 3040 - 3140 cm^-1 region in IR spectra.

-CH stretch modes in alkanes appear in 2850 - 3000 cm^-1 region in IR spectra.

-OH stretch modes appear between in 3000 - 3500 cm^-1 region in IR spectra as a broad peak.

ethereal C-O-C stretch modes appear between in 1070 - 1150 cm^-1 region in IR spectra.

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The peak for a bond with higher force constant appears at higher wave number. The peak for a bond with higher reduced mass appears at lower wave number.