Infrared Spectroscopy, Example #2

IR Spectrum

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C₈H₈O

From the molecular formula, the compound has "5 degrees of unsaturation" (five double bonds, carbonyls or rings). The large number suggests the possible presence of an aromatic ring (4 degrees of unsaturation).

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3400-3200 cm^-1:	no OH or NH present
3100 cm^-1:	moderate peak suggesting unsaturated CH
2900 cm^-1:	weak peak indicating possible saturated CH
2200 cm^-1:	no unsymmetrical triple bonds
1690 cm^-1:	strong carbonyl absorbance
1610 cm^-1:	weak absorbance bands consistent with carbon-carbon double bonds

The spectrum seems to be consistent with a carbonyl compound containing both single and double bonds. The carbonyl absorbance occurs at a relatively low wave number, suggesting the carbonyl is conjugated with a double bond or an aromatic ring. The large number of degrees of unsaturation suggest the presence of an aromatic ring.

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Structure:

IUPAC Name: acetophenone

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Correlation Table	Common Absorbances	Interpret IR
Give Structure	Next Example	Return to IR Home