Modern valence bond description of the electronic mechanisms of S(N)2 identity reactions

J J  Blavins; D L  Cooper; P B  Karadakov

doi:10.1021/jp037348b

Modern valence bond description of the electronic mechanisms of S(N)2 identity reactions

J J Blavins, D L Cooper, P B Karadakov

Chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

Series of ab initio modern valence bond calculations, based on spin-coupled (SC) theory, along the MP2(fc)/6-31G(d,p) minimum-energy paths, are used to examine the electronic rearrangements that take place during the gas-phase S(N)2 identity reactions of Cl- with RCl, where R is methyl, ethyl, or tert-butyl. The corresponding reaction of F- with CH3F is also considered. The SC descriptions of the two CH3X + X- reactions (X = F or Cl) are found to be qualitatively similar, but there is a significantly larger extent of bond formation at the transition state for the fluorine case, and the electronic rearrangements also start much sooner. Comparing CH3Cl + Cl- and CH3CH2Cl + Cl-, the SC calculations suggest that the electronic structure reorganization is largely unaffected by the presence of the additional methyl group. The description of the transition state for the corresponding gas-phase S(N)2 identity reaction of (CH3)(3)CCl is found to be radically different: it is held together by predominantly ionic interactions and most closely resembles a carbocation clamped" between two chloride ions.

Original language	English
Pages (from-to)	914-920
Number of pages	7
Journal	Journal of Physical Chemistry A
Volume	108
Issue number	5
DOIs	https://doi.org/10.1021/jp037348b
Publication status	Published - 5 Feb 2004

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title = "Modern valence bond description of the electronic mechanisms of S(N)2 identity reactions",

abstract = "Series of ab initio modern valence bond calculations, based on spin-coupled (SC) theory, along the MP2(fc)/6-31G(d,p) minimum-energy paths, are used to examine the electronic rearrangements that take place during the gas-phase S(N)2 identity reactions of Cl- with RCl, where R is methyl, ethyl, or tert-butyl. The corresponding reaction of F- with CH3F is also considered. The SC descriptions of the two CH3X + X- reactions (X = F or Cl) are found to be qualitatively similar, but there is a significantly larger extent of bond formation at the transition state for the fluorine case, and the electronic rearrangements also start much sooner. Comparing CH3Cl + Cl- and CH3CH2Cl + Cl-, the SC calculations suggest that the electronic structure reorganization is largely unaffected by the presence of the additional methyl group. The description of the transition state for the corresponding gas-phase S(N)2 identity reaction of (CH3)(3)CCl is found to be radically different: it is held together by predominantly ionic interactions and most closely resembles a carbocation clamped{"} between two chloride ions.",

author = "Blavins, {J J} and Cooper, {D L} and Karadakov, {P B}",

year = "2004",

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doi = "10.1021/jp037348b",

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journal = "Journal of Physical Chemistry A",

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TY - JOUR

T1 - Modern valence bond description of the electronic mechanisms of S(N)2 identity reactions

AU - Blavins, J J

AU - Cooper, D L

AU - Karadakov, P B

PY - 2004/2/5

Y1 - 2004/2/5

N2 - Series of ab initio modern valence bond calculations, based on spin-coupled (SC) theory, along the MP2(fc)/6-31G(d,p) minimum-energy paths, are used to examine the electronic rearrangements that take place during the gas-phase S(N)2 identity reactions of Cl- with RCl, where R is methyl, ethyl, or tert-butyl. The corresponding reaction of F- with CH3F is also considered. The SC descriptions of the two CH3X + X- reactions (X = F or Cl) are found to be qualitatively similar, but there is a significantly larger extent of bond formation at the transition state for the fluorine case, and the electronic rearrangements also start much sooner. Comparing CH3Cl + Cl- and CH3CH2Cl + Cl-, the SC calculations suggest that the electronic structure reorganization is largely unaffected by the presence of the additional methyl group. The description of the transition state for the corresponding gas-phase S(N)2 identity reaction of (CH3)(3)CCl is found to be radically different: it is held together by predominantly ionic interactions and most closely resembles a carbocation clamped" between two chloride ions.

AB - Series of ab initio modern valence bond calculations, based on spin-coupled (SC) theory, along the MP2(fc)/6-31G(d,p) minimum-energy paths, are used to examine the electronic rearrangements that take place during the gas-phase S(N)2 identity reactions of Cl- with RCl, where R is methyl, ethyl, or tert-butyl. The corresponding reaction of F- with CH3F is also considered. The SC descriptions of the two CH3X + X- reactions (X = F or Cl) are found to be qualitatively similar, but there is a significantly larger extent of bond formation at the transition state for the fluorine case, and the electronic rearrangements also start much sooner. Comparing CH3Cl + Cl- and CH3CH2Cl + Cl-, the SC calculations suggest that the electronic structure reorganization is largely unaffected by the presence of the additional methyl group. The description of the transition state for the corresponding gas-phase S(N)2 identity reaction of (CH3)(3)CCl is found to be radically different: it is held together by predominantly ionic interactions and most closely resembles a carbocation clamped" between two chloride ions.

U2 - 10.1021/jp037348b

DO - 10.1021/jp037348b

M3 - Article

SN - 1089-5639

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JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

IS - 5

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