Due to the reactive nature of the carbonyl (C=O) group in aldehydes and ketones, substituents may be added to groups containing aldehydes and ketones to reduce the carbonyl reactivity; aldehydes and ketones with attached carbon chains may have resonance from the carbonyl group as well.
Effects on the substituents on the reactivity of C=O; steric hindrance
The reactive nature of the carbonyl group may not be desired until certain steps when completing a reaction involving aldehydes and ketones. Bulky groups (benzyl groups, for example, can be added in order to reduce the reactivity of the carbonyl group.
The acidity of α-H; carbanions
The alpha (α) carbon (carbon directly adjacent to the carbonyl carbon) is considered stable; when a carbanion is formed at the alpha carbon, it is considered acidic due to its ability to be stabilized by resonance via interactions with the C=O electrons; double bond may be reduced to aid stability.
- Bulky groups like cyclic rings may be used adjacent to the carbonyl group in aldehydes and ketones to reduce the reactivity of the C=O.
- The alpha carbon can be stabilized via resonance from the C=O.
- Carbanion: carbon atom with a negative charge.