Hydrogen bonds involving polar C–H groups. Part 7. Electron-deficient cyclohexenones as analogues of carboxylic acid dimers, and the crystal and molecular structure of 5,5-dimethyl-3-methylsulphonylcyclohex-2-enone

Abstract

Three 3-sulphonylcyclohex-2-enones have been prepared as potential C–H analogues of carboxylic acid dimers, the molecules being designed to associate as doubly bridged hydrogen-bonded dimers via their alkene C–H groups. ¹H N.m.r. and i.r. spectra show no evidence of such an association. The crystal and molecular structure of the title compound has been determined from X-ray diffraction data by direct methods and refined to R 0.034 for 2 008 independent reflections. The crystals are monoclinic, a= 10.243(1), b= 8.755(2), c= 11.672(2)Å, β= 102.94(1)°(at 153 K), space group P2₁/c, and Z= 4. Although the molecules associate as dimers, the H ⋯ O distance (2.63 Å) is too long to be described as a hydrogen bond. The association probably arises from dipole–dipole attractions between the polarised C–H groups and the carbonyl oxygen atoms of the two molecules.