THE formation of stable solid hydrates is well known for aldehydes and
ketones containing several electronegative substituents and for some diand
triketones. The classical example is chloral hydrate, for which there
is direct evidence from proton magnetic resonance measurements
(Bishop and Richards, 1959) and from Raman spectra (Hibben, 1931) for
the gem-diol formula CCl,.CH(OH)2, rather than any looser mode of
hydration. The majority of carbonyl compounds do not give solid hydrates,
except sometimes at low temperatures, but there is frequently
evidence for the reaction RlR2C0 + H20+R1R2C(OH)2 in aqueous
solvents: this is accompanied by the disappearance or weakening of
the characteristic U.V. absorption band of the carbonyl group at about
280 mp, again confirming the nature of the hydrate.