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Which molecules contain an IR stretching frequency of 1680-1740 cm-1?
I. alcohols
II. carboxylic acids
III. nitriles
IV. amides

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Correct Answer: C. II and IV
All carbonyl compounds absorb in the region 1760-1665 cm-1 due to the stretching vibration of the C=O bond. Different carbonyl compounds absorb in narrow ranges within this general region. Carboxylic acids and amides contain carbonyl functionality. Alcohols have broad absorption at approx. 3200-3500 cm-1; nitriles show absorptions at approx. 2250 cm-1.
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