A nuclear magnetic resonance determination of the barrier to internal rotation in phenylethane |
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Authors: | Ted Schaefer Leonard Kruczynski Walter Niemczura |
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Affiliation: | Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 |
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Abstract: | The long-range nuclear spin-spin coupling constant between the methylene protons and the ring protons at the para position in 3,5-dibromo-phenylethane in benzene solution is consistent with a two-fold barrier of 1.2 ± 0.1 kcal/mole to rotation about the sp2-sp3 carbon-carbon bond, in agreement with thermodynamic data on phenylethane and with deductions based on hyperfine interactions in related radical anions. The low-energy conformation has a plane of symmetry, the methyl group being situated out of the aromatic plane, in disagreement with Raman depolarization data interpretations and with deductions based on proton chemical shifts. |
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