TRAJECTORY STUDIES OF S(N)2 NUCLEOPHILIC-SUBSTITUTION .4. INTRAMOLECULAR AND UNIMOLECULAR DYNAMICS OF THE CL-...CH3BR AND CLCH3...BR- COMPLEXES

被引:98
作者
WANG, HB [1 ]
PESLHERBE, GH [1 ]
HASE, WL [1 ]
机构
[1] WAYNE STATE UNIV,DEPT CHEM,DETROIT,MI 48202
关键词
D O I
10.1021/ja00100a032
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Classical trajectory calculations, performed on an analytic potential energy function derived from ah initio calculations, are used to study the intramolecular and unimolecular dynamics of the Cl----CH3Br complex with initial mode specific excitation. Two distinct patterns are observed in the dynamics of this complex. When the low-frequency modes are excited, the complex preferentially dissociates to Cl- + CH3Br. However, when the high-frequency CH3Br intramolecular modes are excited, the above is a negligible reaction path and, instead, Cl----CH3Br --> ClCH3---Br- becomes important. Contrary to RRKM theory, the ClCH3-Br- complexes formed by this isomerization do not immediately dissociate to ClCH3 + Br- but remain trapped in the central barrier region of the potential energy surface, with extensive barrier recrossings. The intramolecular dynamics of Cl----CH3Br and ClCH3---Br- are interpreted in terms of intermolecular and intramolecular complexes, with the former accessing the dissociation products and the latter the central barrier region. There is a dynamical bottleneck for transitions between these two complexes. The ClCH3 f Br product energies, for ClCH3---Br- complexes which do dissociate, are in agreement with the previous experimental study of Graul and Bowers [J. Am. Chem. Sec. 1991, 113, 9696].
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页码:9644 / 9651
页数:8
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