THEORETICAL-STUDY OF SUBSTITUENT EFFECTS IN THE UNIMOLECULAR DECOMPOSITION OF N-CHLORO-ALPHA-AMINO ACID ANIONS - ANALYSIS OF TRANSITION STRUCTURE AND MOLECULAR REACTION-MECHANISM

The unimolecular decomposition of substituted N-chloro-alpha-glycine a nions was examined by an ab initio method using the 6-31G basis set t o obtain an insight into the relationship between transition-state str ucture and reactivity. The complete potential energy surface was explo red and the stationary points corresponding to reactant and transition structure were localized. A reaction analysis by correlation of bond orders revealed that the reaction mechanism corresponds to an asynchro nous fragmentation. The transition structure for all the compounds has an antiperiplanar conformation between the C-C and N-Cl bond breaking and it has a product-like character. The influence of the substitutio n on the alpha-carbon and on the nitrogen is discussed. When the size and number of substituents on the alpha-carbon and to a lesser extent on the nitrogen atom increase the relative energy decreases. The size of the substituent produces perpendicular effects and the type and num ber of substituents give parallel effects.