Thermal decomposition of the benzyl radical to fulvenallene (C 7H 6) + H

Document Type

Article

Publication Date

5-28-2009

Abstract

We show that the benzyl radical decomposes to the C 7H 6 fragment fulvenallene (+H), by first principles/ RRKM study. Calculations using G3X heats of formation and B3LYP/6-31G(2df,p) structural and vibrational parameters reveal that the reaction proceeds predominantly via a cyclopentenyl-allene radical intermediate, with an overall activation enthalpy of ca. 85 kcal mol -1. Elementary rate constants are evaluated using Eckart tunneling corrections, with variational transition state theory for barrierless C-H bond dissociation in the cyclopentenyl-allene radical. Apparent rate constants are obtained as a function of temperature and pressure from a time-dependent RRKM study of the multichannel multiwell reaction mechanism. At atmospheric pressure we calculate the decomposition rate constant to be k [s -1] = 5.93 × 10 35 T -6.099 exp(-49 180/7); this is in good agreement with experiment, supporting the assertion that fulvenallene is the C 7H 6 product of benzyl decomposition. The benzyl heat of formation is evaluated as 50.4 to 52.2 kcal mol-1, using isodesmic work reactions with the G3X theoretical method. Some novel pathways are presented to the cyclopentadienyl radical (C 5H 5) + acetylene (C 2H 2), which may constitute a minor product channel in benzyl decomposition. © 2009 American Chemical Society.

Identifier

66249091962 (Scopus)

Publication Title

Journal of Physical Chemistry A

External Full Text Location

https://doi.org/10.1021/jp901933x

ISSN

10895639

First Page

6111

Last Page

6120

Issue

21

Volume

113

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