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
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.