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Title: Thermal bridgehead double inversion of the 6-methylene-and 6-ethylidene-2-methylbicyclo(3. 1. 0) hexanes and related materials. Rotational kinetic deuterium isotope effects and the mechanism of the thermal interconversion of cis- and trans-2,3-dimethylmethylenecyclopropanes via orthogonal and planar trimethylenemethane singlet biradicals

Abstract

Endo- and exo-2-methyl-6-methylenebicyclo(3.1.0)hexane (N and X) interconverted at 164/sup 0/C at a rate comparable to that for cis to trans isomerization of the 2,3-dimethylmethylenecyclopropanes (C and T) allowing the possibility that the planar trimethylenemethane singlet is responsible for the racemization observed with optically active T. Pyrolysis of the four 2-methyl-6-ethylidenebicyclo(3.1.0)hexanes revealed an average of 8 percent preservation of the exo ethylidene stereochemistry in the bridgehead double inversion reaction. The kinetic deuterium isotope effect on the interconversion of endo- and exo-6,2-methyl-6-dideuteriomethylenebicyclo(3.1.0)hexanes, k/sub H/sub 2///k/sub D/sub 2// = 1.08 +- 0.02, suggests that exo methylene rotation occurs after rate-determining formation of a planar trimethylenemethane biradical since exo methylene rotation in the formation of anti- and syn-2-methylethylidenecyclopropane from trans-2,3-dimethyldideuteriomethylenecyclopropane has an isotope effect of 1.31 +- 0.04. Detailed mechanisms for the stereochemical and kinetic data from pyrolysis of T and C which involve mainly orthogonal and, to a lesser extent, planar or bisorthogonal trimethylenemethane biradicals are presented. The origin and magnitude of rotational kinetic isotope effects in these interconversions is discussed.

Authors:
;
Publication Date:
Research Org.:
Indiana Univ., Bloomington
OSTI Identifier:
7087556
Resource Type:
Journal Article
Journal Name:
J. Am. Chem. Soc.; (United States)
Additional Journal Information:
Journal Volume: 99:17
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; DEUTERIUM; ISOTOPE EFFECTS; ALKANES; CYCLOALKANES; STEREOCHEMISTRY; HYDROCARBONS; HYDROGEN ISOTOPES; ISOTOPES; LIGHT NUCLEI; NUCLEI; ODD-ODD NUCLEI; ORGANIC COMPOUNDS; STABLE ISOTOPES; 400302* - Organic Chemistry- Isotope Effects- (-1987)

Citation Formats

Gajewski, J J, and Chou, S K. Thermal bridgehead double inversion of the 6-methylene-and 6-ethylidene-2-methylbicyclo(3. 1. 0) hexanes and related materials. Rotational kinetic deuterium isotope effects and the mechanism of the thermal interconversion of cis- and trans-2,3-dimethylmethylenecyclopropanes via orthogonal and planar trimethylenemethane singlet biradicals. United States: N. p., 1977. Web. doi:10.1021/ja00459a030.
Gajewski, J J, & Chou, S K. Thermal bridgehead double inversion of the 6-methylene-and 6-ethylidene-2-methylbicyclo(3. 1. 0) hexanes and related materials. Rotational kinetic deuterium isotope effects and the mechanism of the thermal interconversion of cis- and trans-2,3-dimethylmethylenecyclopropanes via orthogonal and planar trimethylenemethane singlet biradicals. United States. https://doi.org/10.1021/ja00459a030
Gajewski, J J, and Chou, S K. Wed . "Thermal bridgehead double inversion of the 6-methylene-and 6-ethylidene-2-methylbicyclo(3. 1. 0) hexanes and related materials. Rotational kinetic deuterium isotope effects and the mechanism of the thermal interconversion of cis- and trans-2,3-dimethylmethylenecyclopropanes via orthogonal and planar trimethylenemethane singlet biradicals". United States. https://doi.org/10.1021/ja00459a030.
@article{osti_7087556,
title = {Thermal bridgehead double inversion of the 6-methylene-and 6-ethylidene-2-methylbicyclo(3. 1. 0) hexanes and related materials. Rotational kinetic deuterium isotope effects and the mechanism of the thermal interconversion of cis- and trans-2,3-dimethylmethylenecyclopropanes via orthogonal and planar trimethylenemethane singlet biradicals},
author = {Gajewski, J J and Chou, S K},
abstractNote = {Endo- and exo-2-methyl-6-methylenebicyclo(3.1.0)hexane (N and X) interconverted at 164/sup 0/C at a rate comparable to that for cis to trans isomerization of the 2,3-dimethylmethylenecyclopropanes (C and T) allowing the possibility that the planar trimethylenemethane singlet is responsible for the racemization observed with optically active T. Pyrolysis of the four 2-methyl-6-ethylidenebicyclo(3.1.0)hexanes revealed an average of 8 percent preservation of the exo ethylidene stereochemistry in the bridgehead double inversion reaction. The kinetic deuterium isotope effect on the interconversion of endo- and exo-6,2-methyl-6-dideuteriomethylenebicyclo(3.1.0)hexanes, k/sub H/sub 2///k/sub D/sub 2// = 1.08 +- 0.02, suggests that exo methylene rotation occurs after rate-determining formation of a planar trimethylenemethane biradical since exo methylene rotation in the formation of anti- and syn-2-methylethylidenecyclopropane from trans-2,3-dimethyldideuteriomethylenecyclopropane has an isotope effect of 1.31 +- 0.04. Detailed mechanisms for the stereochemical and kinetic data from pyrolysis of T and C which involve mainly orthogonal and, to a lesser extent, planar or bisorthogonal trimethylenemethane biradicals are presented. The origin and magnitude of rotational kinetic isotope effects in these interconversions is discussed.},
doi = {10.1021/ja00459a030},
url = {https://www.osti.gov/biblio/7087556}, journal = {J. Am. Chem. Soc.; (United States)},
number = ,
volume = 99:17,
place = {United States},
year = {1977},
month = {8}
}