Theoretical calculations on the gas-phase thermal decomposition kinetics of selected thiomethyl chloroalkanes: A new insight of the mechanism

Marniev Luiggi, José R. Mora, Marcos Antonio Loroño Gonzalez, Edgar Marquez, Jesus Lezama, Tania Cordova, Gabriel Chuchani

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

Theoretical calculations of the gas-phase thermal decomposition kinetics of 2-thiomethyl-1-chloroethane and 4-thiomethyl-1-chlorobutane have been carried out by using Density Functional Theory (DFT), composite CBS-Q3, and Møller-Plesset second-order (MP2) methods in order to elucidate a reasonable reaction mechanism of these compounds. The enhanced reactivities of these two substrates, when compared with their parent compounds, attributed to neighboring group participation (NGP) or anquimeric assistance in the literature, were investigated. For 2-thiomethyl-1-chloroethane two dehydrochlorinaton pathways, with and without NGP were studied. The results of quantum chemical estimations of 2-thiomethyl-1-chloroethane in the gas phase show good agreement with experimental values at B3LYP/6-31++G(2d,p) level, and suggest the 1,2-elimination through non-synchronous four-membered cyclic transition state is the preferred mechanism. For 4-thiomethyl-1-chlorobutane, the significant increase in rate compared to 2-thiomethyl-1-chloroethane, together with the formation of a cyclic product tetrahydrothiophene suggest the anchimeric assistance by the CH3S group in the transition state. Best calculated parameters were obtained with CAM-B3LYP/6-31G++(2d,p). Results support the NGP of the thiomethyl group, through cyclic ion-pair type of intermediate. The bond polarization of the C-Cl, in the direction of Cδ+⋯Clδ-, appears to be the rate determining step of these decompositions.

Original languageEnglish
Pages (from-to)165-172
Number of pages8
JournalComputational and Theoretical Chemistry
Volume1027
DOIs
StatePublished - 1 Jan 2014
Externally publishedYes

Bibliographical note

Copyright:
Copyright 2013 Elsevier B.V., All rights reserved.

Keywords

  • 2-Thiomethyl-1-chloroethane
  • 4-Thiomethyl-1-chlorobutane
  • Kinetics
  • Theoretical calculations
  • Thermal decomposition

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