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

摘要

The unimolecular decomposition of substituted N-chloro-α-glycine anions was examined by an ab initio method using the 6-31G~* basis set to obtain an insight into the relationship between transition-state structure and reactivity. The complete potential energy surface was explored 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 asynchronous 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 substitution on the a-carbon and on the nitrogen is discussed. When the size and number of substituents on the α-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 number of substituents give parallel effects.