Conformational preference of trans-3,5-cyclohexadiene-1,2-diol, a benzene metabolite, from circular dichroism, molecular mechanics and X-ray diffraction study

Abstract

(S,S)-(+)-3,5-Cyclohexadiene-1,2-diol, (S,S)- 1, displays positive π-π* Cotton effect, Δε +10.0 at 256 nm in methanol. Variable-temperature CD measurements in alcohol solvent indicate that the conformer with equatorial hydroxy groups is more stable than the diaxial one (ΔG° = 0.71 kcal/mol). The diaxial conformer has one order of magnitude higher rotational strength compared to the diequatorial one, due to the effect of the allylic axial CO bonds. The diequatorial conformer is stabilized by electrostatic interactions (MMX calculation) and by intramolecular hydrogen bond formation in non-polar solvents. X-ray diffraction study shows that the diequatorial conformer of (S,S)- 1 is present in the crystalline state.