Frequently Asked Question

The reactivity of a carbonyl group is significantly influenced by nearby substituents, both polar and bulky, as well as conjugation effects. Here's a breakdown:
Polar Substituents:
Electron-withdrawing groups (EWGs) like halogens, nitro groups, or cyano groups increase the electrophilicity of the carbonyl carbon by drawing electron density away from it. This makes the carbonyl group more susceptible to nucleophilic attack.
Electron-donating groups (EDGs) like alkyl groups or alkoxy groups decrease the electrophilicity of the carbonyl carbon by pushing electron density towards it. This makes the carbonyl group less reactive towards nucleophiles.
Bulky Substituents:
Steric hindrance from bulky substituents can hinder nucleophilic attack by blocking access to the carbonyl carbon. This effect is more pronounced with larger substituents.
Conjugation:
Conjugation with a pi system, like in an aromatic ring or an alkene, can delocalize the electron density of the carbonyl group, making it less electrophilic and therefore less reactive towards nucleophiles. This is because the electron density is spread over a larger area, making the carbonyl carbon less positive.
Overall, the interplay of these factors determines the reactivity of a carbonyl group. For example, a carbonyl group with an electron-withdrawing group and no bulky substituents will be highly reactive towards nucleophiles. Conversely, a carbonyl group with an electron-donating group and a bulky substituent will be less reactive.