ABSTRACT:A systematic quantum chemical study reveals the effects of chirality on the intermolecular interactions between two chiral molecules bound by hydrogen bonds. The methods used are second-order Møller-Plesset perturbation theory (MP2) with the 6-311ϩϩg(d,p) basis set. Complexes via the OOH⅐⅐⅐O hydrogen bond formed between the chiral 2-methylol oxirane (S) and chiral HOOH (P and M) molecules have been investigated, which lead to four diastereomeric complexes. The nomenclature of the complexes used in this article is enantiomeric configuration sign corresponding to English letters. Such as: sm, sp. The relative positions of the methylol group and the hydrogen peroxide are designated as syn (same side) and anti (opposite side). The largest chirodiastaltic energy was ⌬E chir ϭ Ϫ1.329 kcal mol Ϫ1 [9% of the counterpoise correct average binding energy D e (corr)] between the sm-syn and sp-anti in favor of sm-syn. The largest diastereofacial energy was Ϫ1.428 kcal mol Ϫ1 between sm-syn and sm-anti in favor of sm-syn. To take into account solvents effect, the polarizable continuum model (PCM) method has been used to evaluate the chirodiastaltic energies, and diastereofacial energies of the 2-methylol oxirane⅐⅐⅐HOOH complexes. The chiral 2,3-dimethylol oxirane (S, S) is C 2 symmetry which offers two identical faces. Hence, the chirodiastaltic energy is identical to the diastereomeric energy, and is ⌬E chir ϭ 0.563 kcal mol Ϫ1 or 5.3% of the D e (corr) in favor of s,s-p. The optimized structures, interaction energies, and chirodiastaltic energies for various isomers were estimated. The harmonic frequencies, IR intensities, rotational constants, and dipole moments were also reported.
A theoretical study was reported on the chiral discrimination of different chiral formers of hydrogen-bonded complexes of butan-2-ol (m-form of "ga," "ag," and "gg") with hydrogen peroxide. This completes, together with previous results on the butan-2-ol (h-form)⅐⅐⅐HOOH complexes [Zhang et al., J Mol Struct (Theochem), 2008, 864, 56], the study of two forms of butan-2-ol: m-form and h-form. Altogether, 12 minimum structures were located, and they are bound by intermolecular hydrogen bonds. The largest chirodiastaltic energy of the two most stable complexes was found for (SM-2)-(SP-2) of "gg", at Ϫ0.238 kcal mol Ϫ1 in favor of the SM-2 complex in the "gg" configuration. The largest diastereofacial energy was found for (SP-2)-SP of "ga," at Ϫ3.763 kcal mol Ϫ1 in favor of the SP-2 complex in the "ga" configuration. Moreover, the diastereofacial interactions lead to a preference for the SM-2 and SP-2 over the SM and SP for all the butan-2-ol (m-form)⅐⅐⅐HOOH complexes. The values of the largest chirodiastaltic energy and diastereofacial energy are similar to butan-2-ol (h-form), but the sign of the value (diastereofacial energy) is reverse.
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