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Density Functional Study on the Reactivity of Carbenes Toward 1,2‐H Shifts
Author(s) -
Hu ChingHan
Publication year - 2001
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.200100002
Subject(s) - chemistry , carbene , singlet state , reactivity (psychology) , substituent , density functional theory , exothermic reaction , activation energy , crystallography , computational chemistry , medicinal chemistry , stereochemistry , catalysis , organic chemistry , atomic physics , medicine , physics , alternative medicine , pathology , excited state
The 1,2‐H shift reactions of simple carbenes (CH 2 Y‐C‐X) have been studied using density functional theory (DFT). The influence of the substituent X and Y groups on the activation energy (Ea) of 1,2‐H shifts were examined. The ‘by stander’ Y substituents lower E a in the order of Me, F > Cl, Br > H. Our analysis shows that the X effect is more significant than the by stander Y effect. X substitutions increase E a of carbenes in the order of F > Cl > Br > Me > H. The influence of X on E a is governed by the singlet‐triplet energy separation (ΔE S‐T ) of the carbene, i.e., E a of a carbene is larger as its ΔE S‐T in creases due to an X substitution. The X effect was also found to be related to the magnitude of the exothermicity: Ea of reaction is smaller when the reaction is more exothermic. Origin of the Y effect is attributed to the inter play between two factors: ‘lateness’ of transition state on the potential energy surface, and the exothermicity of the reaction.