Cycloalkylmethyl radicals. Part 8. A conformational study of dioxa- and dithia-cyclohexylmethyl radicals by EPR spectroscopy

Finlay MacCorquodale, John C. Walton*, Lise Hughes, Keith U. Ingold

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)

Abstract

The conformations of some six-membered oxygen- and sulphur-containing heterocyclic rings have been investigated by EPR spectroscopy using the methylenyl group, CH2, directly attached to a ring carbon atom as a 'spin probe'. For the 2-oxacyclohexylmethyl radical the CH2 group has a 'conformational free energy' preference for the equatorial position, -ΔG°273 = 1.4 kcal mol-1, which is about twice as large as the 0.7 kcal mol-1 found previously for cyclohexylmethyl. The equatorial preference of the CH2 group is still greater in (1,3-dioxan-2-yl)methyl radicals; indeed, even with the cis-(5-tert-butyl-1,3-dioxan-2-yl)methyl radical the CH2 group was equatorial and the tert-butyl group axial. The CH2 group in (1,3-dioxan-5-yl)methyl also exhibits a strong preference for the equatorial position (ΔG° > ca. 1.5 kcal mol-1), but with cis-(2-methyl-1,3-dioxan-5-yl)methyl it is the methyl group which is equatorial and the CH2 group axial. These and other axial/equatorial conformational preferences and the rotational conformational preference of the plane of the CH2 group with respect to the Cβ-Hβ bond are rationalized in terms of subtle steric factors which involve 1,3-axial/axial interactions, or lack thereof, and the variation in the lengths of C-C, C-O and C-S bonds.

Original languageEnglish
Pages (from-to)1893-1899
Number of pages7
JournalJournal of the Chemical Society, Perkin Transactions 2
Issue number12
Publication statusPublished - 1 Dec 1991

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