Which functional group can be identified by a strong, broad absorption around $3300$ cm$-1$ using IR spectroscopy?

• A. Nitrile ($C_N$ triple bond)
• B. Alcohol ($O_H$ group)
• C. Ester ($C_O$ stretch)
• D. Aldehyde ($C_H$ stretch)

Answer: (B)

Verified step by step guidance

1. Understand that IR spectroscopy identifies functional groups based on characteristic absorption frequencies related to bond vibrations.
2. Recall that a strong, broad absorption around 3300 cm\(\textsuperscript{-1}\) typically corresponds to O-H stretching vibrations, which are characteristic of alcohols and sometimes carboxylic acids.
3. Compare this with other functional groups: nitriles (C≡N) absorb sharply near 2250 cm\(\textsuperscript{-1}\), esters (C=O) show strong absorption near 1735-1750 cm\(\textsuperscript{-1}\), and aldehydes (C-H) have absorptions around 2700-2900 cm\(\textsuperscript{-1}\).
4. Note that the broadness of the peak is due to hydrogen bonding in O-H groups, which is not present in nitriles, esters, or aldehydes, making the broad peak around 3300 cm\(\textsuperscript{-1}\) distinctive for alcohols.
5. Conclude that the functional group with a strong, broad absorption near 3300 cm\(\textsuperscript{-1}\) in IR spectroscopy is the alcohol (O-H) group.