The IR absorption near 1700 cm−1 is characteristic of which functional group?

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Multiple Choice

The IR absorption near 1700 cm−1 is characteristic of which functional group?

Explanation:
In infrared spectroscopy, functional groups have characteristic absorption regions, and the carbonyl C=O bond is known for a strong, distinctive stretch near 1700 cm−1. This vibration causes a large change in dipole moment as the bond lengthens and shortens, so it absorbs strongly in that region. The typical range is about 1650–1750 cm−1, with subtle shifts depending on conjugation or the surrounding framework. For comparison, alkane C–H stretches show up around 2850–2960 cm−1, nitrile C≡N stretches near 2200–2250 cm−1, and alcohol O–H stretches are broad and usually appear around 3200–3600 cm−1. That’s why the absorption near 1700 cm−1 points to a carbonyl-containing compound.

In infrared spectroscopy, functional groups have characteristic absorption regions, and the carbonyl C=O bond is known for a strong, distinctive stretch near 1700 cm−1. This vibration causes a large change in dipole moment as the bond lengthens and shortens, so it absorbs strongly in that region. The typical range is about 1650–1750 cm−1, with subtle shifts depending on conjugation or the surrounding framework.

For comparison, alkane C–H stretches show up around 2850–2960 cm−1, nitrile C≡N stretches near 2200–2250 cm−1, and alcohol O–H stretches are broad and usually appear around 3200–3600 cm−1. That’s why the absorption near 1700 cm−1 points to a carbonyl-containing compound.

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