Theoretical study of the mechanism for the gas‐phase pyrolysis kinetics of 2‐methylbenzyl chloride |
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| Authors: | Edgar Marquez Jose R Mora Tania Cordova Gabriel Chuchani |
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| Institution: | 1. Departamento de Química, Escuela de Ciencias, Universidad de Oriente Núcleo Sucre, Cumana, Venezuela;2. Centro de Química, Instituto Venezolano de Investigaciones Científicas (I.V.I.C.), Apartado 21827, Caracas 1020.A, Venezuela;3. Department of Medicinal Chemistry, College of Pharmacy, University of Florida. P.O Box. 100485. Gainesville, FL 32610 |
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| Abstract: | The study of the kinetics and mechanism of dehydrochlorination reaction of 2‐methyl benzyl chloride in the gas phase was carried out by means of electronic structure calculations using ab initio Móller‐Plesset MP2/6‐31G(d,p), and Density Functional Theory (DFT) methods: B3LYP/6‐31G(d,p), B3LYP/6‐31++G(d,p), MPW1PW91/6‐31G(d,p), MPW1PW91/6‐31++G(d,p)], PBE/6‐31G(d,p), PBE/6‐31++G(d,p). Investigated reaction pathways comprise: Mechanism I, a concerted reaction through a six‐centered cyclic transition state (TS) geometry; Mechanism II, a 1,3‐chlorine shift followed by beta‐elimination and Mechanism III, a single‐step elimination with simultaneous HCl and benzocyclobutene formation through a bicyclic type of TS. Calculated parameters ruled out Mechanism III and suggest the elimination reaction may occur by either unimolecular Mechanism I or Mechanism II. However, the TS of the former is 20 kJ/mole more stable than the TS of the latter. Consequently, the Mechanism I seem to be more probable to occur. The rate‐determining process is the breaking of C‐Cl bond. The involvement of π‐electrons of the aromatic system was demonstrated by NBO charges and bond order calculations. The reaction is moderately polar in nature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 537–546, 2011 |
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