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Remote Substituent Effects on Homolytic Bond Dissociation Energies.

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Title: Remote Substituent Effects on Homolytic Bond Dissociation Energies.
Authors: Yao Fu, Lei Liu, Bo-Lin Lin, Yi Mou, Yu-Hui Cheng, Qing-Xiang Guo
Source: Journal of Organic Chemistry. 6/13/2003, Vol. 68 Issue 12, p4657. 6p. 1 Diagram, 4 Charts, 6 Graphs.
Subjects: Dissociation (Chemistry), Hammett equation
Abstract: In the study we tried to answer two questions. First, does X-Z homolytic bond dissociation energy (BDE) of Y-C[sub 6]H[sub 4]-X-Z obey the Hammett relationship? Second, if it does what factors determine the magnitude and sign of the slope (ρ[sup +]) of Hammett regression against substituent σ[sub p, sup +] constants? We collected a large number of X-Z BDEs for over one-thousand Y-C[sub 6]H[sub 4]-X-Z systems using the RMP2/6-311++G[sup **]//UB3LYP/6-31G[sup *] 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[sup •] by the substituents). The ground or radical effect is determined by the electron demand of X-Z or X[sup •] in the same way as the deprotonation enthalpy of HOOC-C[sub 6]H[sub 4]-X-Z or HOOC-C[sub 6]H[sub 4]-X[sup •] is affected by X-Z or X[sup •]. As a result, ρ[sup +](BDE) for X-Z bond homolysis can be quantitatively predicted by using the change in deprotonation enthalpy from HOOC-C[sub 6]H[sub 4]-X-Z to HOOC-C[sub 6]H[sub 4]-X[sub •]. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:In the study we tried to answer two questions. First, does X-Z homolytic bond dissociation energy (BDE) of Y-C[sub 6]H[sub 4]-X-Z obey the Hammett relationship? Second, if it does what factors determine the magnitude and sign of the slope (ρ[sup +]) of Hammett regression against substituent σ[sub p, sup +] constants? We collected a large number of X-Z BDEs for over one-thousand Y-C[sub 6]H[sub 4]-X-Z systems using the RMP2/6-311++G[sup **]//UB3LYP/6-31G[sup *] 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[sup •] by the substituents). The ground or radical effect is determined by the electron demand of X-Z or X[sup •] in the same way as the deprotonation enthalpy of HOOC-C[sub 6]H[sub 4]-X-Z or HOOC-C[sub 6]H[sub 4]-X[sup •] is affected by X-Z or X[sup •]. As a result, ρ[sup +](BDE) for X-Z bond homolysis can be quantitatively predicted by using the change in deprotonation enthalpy from HOOC-C[sub 6]H[sub 4]-X-Z to HOOC-C[sub 6]H[sub 4]-X[sub •]. [ABSTRACT FROM AUTHOR]
ISSN:00223263
DOI:10.1021/jo034094h