The SN2 transition state. Part 4: α-substituents and the SN2-SN1 borderline problem in the SN2 identity reaction

Daniel Kost, Kalman Aviram

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

The optimized CH4NH2- (C2v symmetry) SN2 transition state serves as a model to study SN2-SN1 borderline phenomena by application of SCF-MO theory. π-Interactions between the nitrogen lone-pair and the π-type orbital associated with the reaction coordinate, which are repulsive in the SN2 transition state but stabilizing in a carbocation, are examined as a function of C-nucleophile and C-leaving group distances. It is shown that the corresponding Mulliken π-overlap population changes gradually from repulsive (tight SN2 transition state) to attractive (loose, SN1-like transition state), whereas no such change is observed in the "off" conformation, in which the lone pair is turned by 90° relative to the reaction coordinate and overlap is minimal. A distinct geometrical preference is associated with the change in mechanism: in a tight SN2 transition state the nitrogen lone pair is turned to avoid repulsive interaction, while it parallels the reaction coordinate in a loose, SN1-like transition state.

Original languageEnglish
Pages (from-to)163-169
Number of pages7
JournalJournal of Molecular Structure: THEOCHEM
Volume138
Issue number1-2
DOIs
StatePublished - 1 Jan 1986

ASJC Scopus subject areas

  • Biochemistry
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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