PhCHOH2

PhCHOH2 is the benzylic geminal diol Ph-CH(OH)2, the hydrated form of benzaldehyde (Ph-CHO). In this compound the carbon attached to the phenyl ring bears two hydroxyl groups and one hydrogen, giving a tetrahedral center with two identical OH substituents.

Formation and occurrence: In aqueous solution, benzaldehyde hydrates to form the gem-diol, establishing a dynamic equilibrium with benzaldehyde and water. The hydrate is typically not isolated under ordinary conditions and is present only in small amounts, with its fraction depending on temperature, solvent, pH, and substituents on the phenyl ring. Electron-withdrawing substituents on the ring generally favor hydration, while electron-donating substituents tend to resist it.

Structure and properties: The diol exists primarily in solution as Ph-CH(OH)2 and is not commonly obtained as a pure solid. The carbon bearing the two hydroxyl groups is not chiral, since the two OH substituents are identical. The hydrate form is less reactive than the parent aldehyde and readily reverts to benzaldehyde upon loss of water, illustrating a reversible aldehyde hydration equilibrium in aqueous media.

Relevance: PhCHOH2 serves as a classic example in discussions of aldehyde hydration and carbonyl chemistry. It highlights how water interacts with carbonyl compounds and how substituents and conditions influence the extent of hydration.

See also: Hydration (chemistry), geminal diol, benzaldehyde.