STRUCTURE AND ISOMERIZATION OF ALPHA-PHENYLCINNAMIC ACID STEREOISOMERS - REACTION PATHWAY AND TRANSITION-STATE STRUCTURE BY SEMIEMPIRICAL METHODS

The isomerization reaction of E- and Z-alpha-phenylcinnamic acid molec ules was studied at the level of semiempirical quantum chemical method s (MNDO, AM1 and PM3). Calculations revealed that Z-alpha-phenylcinnam ic acid is slightly more stable than the E isomer. The activation enth alpy for isomerization and the transition-state structure were also de termined. The difference in the acidities of the mio stereoisomers of alpha-phenylcinnamic acid and cinnamic acid (this is the basis of thei r separation experimentally) was rationalized by computing the dipole moments of the ions.