Cyanohydrin formation introduces a nitrile group detectable by IR

Steps:

• Propanal, an aldehyde, reacts with HCN to form a cyanohydrin: CH₃CH₂CH(OH)CN.
• The product features a nitrile (-C≡N) functional group.
• IR spectroscopy identifies functional groups via characteristic stretching frequencies.
• The -C≡N stretch appears as a weak band in the 2200-2500 cm⁻¹ region.

Why A is correct:

• Nitrile C≡N triple bond stretching vibration produces a weak absorption at 2200-2500 cm⁻¹, per standard IR correlation tables.

Why the others are wrong:

• B: 3200-3600 cm⁻¹ indicates O-H stretch from the hydroxyl group, but this is not unique to the reaction product.
• C: 1040-1300 cm⁻¹ corresponds to C-O stretch in alcohols, present but not diagnostic for the cyanohydrin formation.

Final answer: A