Entropic intermediates and hidden rate-limiting steps in seemingly concerted cycloadditions. Observation, prediction, and origin of an isotope effect on recrossing.
J Am Chem Soc
; 134(4): 1914-7, 2012 Feb 01.
Article
en En
| MEDLINE
| ID: mdl-22229840
ABSTRACT
An unusual intramolecular kinetic isotope effect (KIE) in the reaction of dichloroketene with cis-2-butene does not fit with a simple asynchronous cycloaddition transition state, but it can be predicted from trajectory studies on a bifurcating energy surface. The origin of the KIE is related to a high propensity for transition state recrossing in this system, with heavier masses recrossing less. The KIE can also be predicted by a statistical model that treats the cycloaddition as a stepwise mechanism, the rate-limiting second step being associated with an entropic barrier for formation of the second carbon-carbon bond. The relevance of this stepwise mechanism to other asynchronous but seemingly concerted cycloadditions is suggested by examination of organocatalytic Diels-Alder reactions.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Entropía
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Dicloroetilenos
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Alquenos
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Cetonas
Tipo de estudio:
Prognostic_studies
/
Risk_factors_studies
Idioma:
En
Revista:
J Am Chem Soc
Año:
2012
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
EEUU
/
ESTADOS UNIDOS
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ESTADOS UNIDOS DA AMERICA
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EUA
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UNITED STATES
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UNITED STATES OF AMERICA
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US
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USA