Homochiral vs. heterochiral preference in chiral self-recognition of cyclic diols.

The structure and clustering propensity of a chiral derivative of cis -1,2-cyclohexanediol, namely, 1-phenyl- cis -1,2-cyclohexanediol ( cis -PCD), has been studied under supersonic expansion conditions by combining laser spectroscopy with quantum chemistry calculations. The presence of the phenyl substituent induces conformational locking relative to cis -1,2-cyclohexanediol ( cis -CD), and only one conformer of the bare molecule is observed by both Raman and IR-UV double resonance spectroscopy. The homochiral preference inferred for the dimer formation at low enough temperature is in line with the formation of a conglomerate in the solid state. The change in clustering propensity in cis -PCD relative to trans -1,2-cyclohexanediol ( trans -CD), which shows heterochiral preference, is explained by the presence of the phenyl substituent rather than the effect of cis-trans isomerism. Indeed the transiently chiral cis -CD also forms preferentially heterodimers, whose structure is very close to that of the corresponding trans -CD dimer.