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Cycloheptatrienyl radicals: An EPR study of substituent effects

✍ Scribed by Finlay MacCorquodale; John C. Walton

Publisher
John Wiley and Sons
Year
1990
Tongue
English
Weight
513 KB
Volume
28
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

Cycloheptatrienyl radicals with donor and acceptor substituents were generated by hydrogen abstraction from the corresponding cycloheptatrienes and studied by EPR spectroscopy. The barrier to rotation about the C‐1ο£ΏCο£ΎO bond in ethoxycarbonylcycloheptatrienyl radicals was found to be ca. 7.5 kcal mol^βˆ’1^ (31.4 kJ mol^βˆ’1^). The observed hyperfine splittings of the ring hydrogens were interpreted in terms of a model in which the substituent causes an energy separation Ξ”__E__ between the frontier orbitals. Populations of the symmetric and antisymmetric orbitals were deduced, and Ξ”__E__ values were estimated. A similar analysis was carried out from EPR data for substituted benzene radical anions. These energy separations show a linear correlation with Hammett constants. The p‐values from plots of this type for [n]annulene radicals decrease in magnitude as the size of the ring increases.

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