SolutionsReactivity
1. Aldehyde or ketone
Rank by reactivity towards nucleophilic addition: acetone, formaldehyde, acetaldehyde and di-tert-butyl ketone. Explain.
Formaldehyde > acetaldehyde > acetone > di-tert-butyl ketone. Alkyl groups stabilize the partial positive charge of the carbonyl carbon (electronic effect) and hinder the approach of the nucleophile (steric effect), more so the bulkier they are.
2. Where does each reagent attack?
Indicate which center of butanone takes part in its reaction with: a) NaBH4; b) LDA; c) H2SO4 (protonation); d) Br2 in acid.
- The carbonyl carbon (electrophilic center): a hydride adds.
- The α hydrogens (acidic): the enolate forms.
- The oxygen (weak Lewis base): the protonated carbonyl forms.
- The nucleophilic α carbon of the enol attacks bromine: α-halogenation.