The most important structural characteristic of aldehydes or ketones is the carbonyl group.
Aldehydes and ketones are carbonyl compounds.
Ketones have carbon atoms attached on either side of the carbonyl carbon.
Aldehydes have either two hydrogen atoms (H₂C=O) or one carbon and one hydrogen (RCH=O)directly attached to the carbonyl carbon.
Most reactions of aldehydes and ketones are the same, because they involve the carbonyl group. Some of these reactions are:
A. Hydration and Hemiacetal formation
R₂CO + R'OH ⇌ R₂C(OH)OR'
B. Acetal Formation
R₂C=O + 2R'OH ⇌ R₂C(OR')₂ + H₂O
C. Formation of Imines and Related Compounds
R₂C=O + H₂NR' ⇌ R₂C(OH)NHR' ⇌ R₂C=NR' + H₂O
D. Formation of Enamines
R₂CH(C=O)R + HNR'₂ ⇌ R₂C=CR-NR'₂ + H₂O
E. Cyanohydrin Formation
R₂C=O + HCN ⇌ R₂C(OH)CN
F. Metal Hydride Reduction
R₂C=O + LiAlH₄ or NaBH₄ → R₂CHOH
G. Addition of Organometallic Compounds
R₂C=O + R'MgBr → R₂R'COMgBr → R₂R'COH
H. Clemmensen Reduction
R₂CO + Zn(Hg) +HCl → RCH₂R
In all the above reactions, the carbonyl group is the site where the reaction takes place.