Remote substituent effects on homolytic bond dissociation energies

Yao Fu; Lei Liu; Bo-Lin Lin; Yi Mou; Yu-Hui Cheng; Qing-Xiang Guo

doi:10.1021/jo034094h

Remote substituent effects on homolytic bond dissociation energies

J Org Chem. 2003 Jun 13;68(12):4657-62. doi: 10.1021/jo034094h.

Authors

Yao Fu¹, Lei Liu, Bo-Lin Lin, Yi Mou, Yu-Hui Cheng, Qing-Xiang Guo

Affiliation

¹ Department of Chemistry, University of Science and Technology of China, Hefei 230026, China.

PMID: 12790568
DOI: 10.1021/jo034094h

Abstract

In the study we tried to answer two questions. First, does X-Z homolytic bond dissociation energy (BDE) of Y-C6H4-X-Z obey the Hammett relationship? Second, if it does what factors determine the magnitude and sign of the slope (rho+) of Hammett regression against substituent sigma(p)(+) constants? We collected a large number of X-Z BDEs for over one-thousand Y-C6H4-X-Z systems using the RMP2/6-311++G**//UB3LYP/6-31G* method. We found that remote substituent effects on X-Z BDEs are determined by both the ground effect (i.e. stabilization/destabilization of X-Z by the substituents) and the radical effect (i.e. stabilization/destabilization of X. by the substituents). The ground or radical effect is determined by the electron demand of X-Z or X. in the same way as the deprotonation enthalpy of HOOC-C6H4-X-Z or HOOC-C6H4-X. is affected by X-Z or X. . As a result, rho+ (BDE) for X-Z bond homolysis can be quantitatively predicted by using the change in deprotonation enthalpy from HOOC-C6H4-X-Z to HOOC-C6H4-X. .