Reaction Force Decomposition of Activation Barriers To Elucidate Solvent Effects

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• 作者：Jaroslav V. Burda ; Alejandro Toro-Labb&eacute ; Soledad Guti&eacute ; rrez-Oliva ; Jane S. Murray ; Peter Politzer
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：April 5, 2007
• 年：2007
• 卷：111
• 期：13
• 页码：2455 - 2457
• 全文大小：96K
• 年卷期：v.111,no.13(April 5, 2007)
• ISSN：1520-5215

文摘

The reaction force F(R_c) of a chemical or physical process is given by the negative derivative of the potentialenergy V(R_c) along the intrinsic reaction coordinate R_c. F(R_c) unambiguously and naturally divides theactivation barrier in each direction into two contributions, one of which has been found to reflect preparativestructural factors, E_act,prep, and the other corresponds to the first part of the transition to products, E_act,trans. Wehave analyzed F(R_c) for an S_N2 substitution reaction in both the gas and aqueous phases. Although the overallforward and reverse activation barriers are significantly lowered by the solvent, the E_act,trans are very littleaffected. Thus the increased rates that are predicted for this process in aqueous solution can be attributed tothe solvent facilitating the structural effects in the preparative stages, decreasing the E_act,prep. This exampleshows how the reaction force decomposition of activation barriers can help to elucidate the roles played byexternal factors, e.g., solvents.