CHIRAL DISCRIMINATION IN HYDROGEN-BONDED COMPLEXES OF 2-METHYLOL OXIRANE WITH ETHANOL

Abstract

We present an ab initio investigation on the chiral discrimination of 2-methylol oxirane (M-olOx)· · · ethanol (EtOH) complexes, for the sake of comparison with previous report on propylene oxide (PO)· · · EtOH complexes. Second-order Møller–Plesset perturbation theory (MP2) with the 6-311++G(d,p) basis set was used to elucidate the diastereomeric interactions between ethanol ( EtOH ), a transient chiral alcohol, and the chiral molecule 2-methylol oxirane (R). Six complexes of M-olOx· · · EtOH have been identified and their structures as well as their calculated stability ordering have been determined. The six complexes were defined in a similar way as for PO· · · EtOH . The primary O–H· · · O hydrogen bonds are predicted to be important contributions to chiral discrimination in M-olOx· · · EtOH . The three syn structures, with ethanol and the methylol group on the same side of the oxirane ring, are energetically favored over the three anti structures. The larger chirodiastaltic energy between synG- and synG+ is 0.52 kJ mol-1. The largest diastereofacial energy between synG- and antiG- is 13.90 kJ mol-1. The obtained results are compared with previously reported results on the PO· · · EtOH complexes and the mechanisms of chiral discrimination in PO· · · EtOH and M-olOx· · · EtOH are discussed. The harmonic frequencies, IR intensities, rotational constants, and dipole moments for the M-olOx· · · EtOH complexes are also presented. Such a theoretical study should be valuable to further spectroscopic investigations on M-olOx· · · EtOH complexes.