Which of the following IR absorption bands would you expect to observe in the functional group region (4000–1500 cm^{-1}) for ethanol (CH_3CH_2OH)?

• A. A strong absorption near 1700 cm^{-1} (C=O stretch) and a medium absorption near 2250 cm^{-1} (C≡N stretch)
• B. A strong absorption near 1600 cm^{-1} (C=C stretch) and a weak absorption near 2100 cm^{-1} (C≡C stretch)
• C. A strong, sharp absorption near 3400 cm^{-1} (N–H stretch) and a strong absorption near 1650 cm^{-1} (amide C=O stretch)
• D. A strong, broad absorption near 3300 cm^{-1} (O–H stretch) and a strong absorption near 2950 cm^{-1} (C–H stretch)

Answer: (D)

Verified step by step guidance

1. Identify the functional groups present in ethanol (CH_3CH_2OH). Ethanol contains an O–H group (hydroxyl) and C–H bonds, but no C=O, C≡N, C=C, C≡C, or N–H groups.
2. Recall the typical IR absorption regions for these functional groups: O–H stretches appear as strong, broad bands around 3200–3600 cm^{-1}, and C–H stretches appear near 2850–3000 cm^{-1}.
3. Understand that a C=O stretch typically appears near 1700 cm^{-1}, C≡N near 2250 cm^{-1}, C=C near 1600 cm^{-1}, C≡C near 2100 cm^{-1}, and N–H near 3300–3500 cm^{-1}, but these are not present in ethanol.
4. Match the expected IR absorption bands for ethanol to the options given: look for a strong, broad absorption near 3300 cm^{-1} corresponding to the O–H stretch and a strong absorption near 2950 cm^{-1} corresponding to the C–H stretch.
5. Conclude that the correct IR absorption bands for ethanol in the functional group region (4000–1500 cm^{-1}) are a strong, broad O–H stretch near 3300 cm^{-1} and a strong C–H stretch near 2950 cm^{-1}.