the interaction between two aldehyde or ketone molecules involving dehydration. For example, the crotonic condensation of acetaldehyde yields crotonalde-hyde (II):
The first stage of crotonic condensation involves aldol condensation, which, in the case of aldehyde, yields aldol (I). This product undergoes dehydration in the second stage. Crotonic condensation occurs under the influence of strong acids (for example, concentrated sulfuric acid) or bases (KOH, NaOH, KCN), usually upon heating. Aldehydes and ketones react only at the a-methylene group and can enter into crotonic condensation with other compounds containing an active CH2 group (for example, with nitro compounds):
CH3CHO + CH3CH2NO2 → CH3CH═C(CH3)NO2 + H2O
Crotonic condensation is used in organic synthesis.