ketone

Meaning: A ketone has a carbonyl group (C=O) whose carbon is bonded to two carbon groups, R–CO–R′. Names end in -one (propanone is acetone). The carbonyl carbon is sp² and partially positive, so nucleophiles attack it, forming a tetrahedral intermediate. Ketones are less reactive than aldehydes because two alkyl groups donate electrons and add steric hindrance. Alpha hydrogens are weakly acidic, allowing enolate formation and keto-enol tautomerism.

On the MCAT: Oxidizing a secondary alcohol (for example with PCC) gives a ketone; NaBH₄ or LiAlH₄ reduces it back. Grignard reagents add to give tertiary alcohols, amines give imines, and alcohols give hemiketals and ketals. Spectra show a strong IR peak near 1700 cm⁻¹ and a ¹³C signal near 200 ppm, with no aldehyde proton near 9–10 ppm. Ketones boil higher than alkanes of similar mass but lower than alcohols, since they accept but cannot donate hydrogen bonds.

Common confusion: An aldehyde has at least one H on the carbonyl carbon, so it oxidizes easily to a carboxylic acid; a ketone has two carbons there and resists mild oxidation. Carboxylic acids, esters and amides also contain C=O, but their carbonyl carbon bears O or N, so they are not ketones.