61728-99-2Relevant articles and documents
Cycloalkylmethyl Radicals. Part 8. A Conformational Study of Dioxa- and Dithia-cyclohexylmethyl Radicals by EPR Spectroscopy
MacCorquodale, Finlay,Walton, John C.,Hughes, Lise,Ingold, Keith U.
, p. 1893 - 1900 (2007/10/02)
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, -ΔG0273 = 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)methylradicals; 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 (ΔG0 > 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.
