Thermochemical and kinetic study of the carbocation ring contraction of cyclohexylium to methylcyclopentylium

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DOIResolve DOI: http://doi.org/10.1021/jp710656f
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TypeArticle
Journal titleThe Journal of Physical Chemistry A
Volume112
Issue17
Pages40044010; # of pages: 7
AbstractThe isomerization of cyclohexylium to methylcyclopentylium is a model for a key step required in sterol and triterpene biosynthesis and is important in catalytic processes associated with ring-opening reactions in upgrading petroleum fractions. Using high-level, correlated wave function techniques based on QCISD, the mechanism for this isomerization was found to be very different from that first proposed more than 35 years ago. On the basis of our mechanism, a first-order rate constant expression was derived and used with complete basis set-extrapolated QCISD(T) energies to obtain Ea = 6.9 kcal/mol and A = 10¹¹⋅¹⁸ s⁻¹, in excellent agreement with values of 7.4 ± 1 kcal/mol and A = 10¹² ±¹⋅³ s⁻¹ measured in the gas phase. The B3LYP and MP2 methods, two commonly used computational approaches, were found to predict incor-rect mechanisms and, in some cases, poor kinetic parameters. The PBE method, however, produced a reac tion profile and kinetic parameters in reasonable agreement with those obtained with the complete basis set-extrapolated QCISD(T) method.
Publication date
PublisherAmerican Chemical Society
AffiliationNRC National Institute for Nanotechnology; National Research Council Canada
Peer reviewedYes
NRC number549
NPARC number8926249
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Record identifierc8d3e894-0525-437b-8b0b-39e6f7875804
Record created2009-04-23
Record modified2017-03-26
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