amygdalic acid, phenylglycolic acid; the simplest aliphatic-aromatic hydroxy acid.

Mandelic acid exists in two optically active forms, ( + ) and ( − ), as well as in the racemic (paramandelic) ( ± ) form. The first two types melt at 133.3°C; the racemic form

melts at 120.5°C. Natural ( − )-mandelic acid occurs in the bitter almond as the glycoside amygdalin, from which it can be extracted by hydrolysis; ( + )-mandelic acid is present (in a bound form) in the fruits and flowers of the common elder; and (±)-mandelic acid is obtained from benzaldehyde: