Density Functional Study on the Reactivity of Carbenes Toward 1,2-H Shifts

[[abstract]]The 1, 2-H shifter actions of simple carbenes (CH2Y-C-X) have been studied using density functional theory (DFT). The influence of the substituent X and Y groups on the activation energy (E(subscript a)) of 1, 2-H shifits were ex am med The 'bystander' Y sub stitu ents lower E(subscript a) in the order of Me, F>C1, Br>H. Our analy sis shows that the X effect is more sig nifi cantthan the by stander Y effect. X substitutions in crease E(subscript a) of carbenes in the order of F>C1>Br>Me>H. The in flu ence of X on E(subscript a) is governed by the singlet-triplet energy separation (△E(subscript S-T)) of the carbene, i.e., E(subscript a) of a carbene is larger as its △E(subscript S-T)in creases due to an X sub stitution. The X effect was also found to be re lated to the magni hide of the exothermicity: E(subscript a) of re action is smaller when there action is more exothermic. Or I gin of the Y effect is at tribeted to the inter play between two factors late ness' of transition state on the potential energy surface, and the exothermicity of the reaction