Molecular Recognition of Chiral Conformers: A Rotational Study of the Dimers of Glycidol

Abstract

Two homochiral dimers of glycidol, deriving from two different conformers, have been characterized by rotational spectroscopy in a supersonic expansion.

Chirped‐Pulse and Cavity‐Based Fourier Transform Microwave Spectra of the Methyl Lactate⋅⋅⋅Ammonia Adduct

“…[20] This is not too surprising since the x direction is least effected by the formation of the OH···N and NH···C=O H-bonds. In the H 3 N···hydrogen halide series where NH 3 serves only as a proton acceptor, a reduction was observed and attributed to the zero-point energy (ZPE) averaging of the large amplitude motions and a small electric perturbation at 14 N. [21] A similar amount of reduction was reported for glycidol···NH 3 . [10] (Please note that there is a typo for the sign of c zz for glycidol···NH 3 and NH 3 in Ref.…”

Chirality Recognition in the Glycidol⋅⋅⋅Propylene Oxide Complex: A Rotational Spectroscopic Study

“…Even with a sample mixture of only PO + Gly + Ne, rotational transitions due to species other than the targeted dimers can show up with fairly strong intensities. For example, those of the PO dimer, [11] the Gly dimers, [12] PO···Ne, [22] and Gly and 13 C Gly, [13] were identified and excluded using the previously measured frequencies. Additional tests to reduce the number of candidate transitions were performed by using the sample mixtures excluding either PO or Gly.…”

“…T rot , the rotational temperature in the jet, was estimated to be about 1 K using a few pairs of rotational transitions observed. Since only the few lowest energy rotational levels are accessed in our experiment, one single rotational temperature is good enough to describe the population distribution of these levels, [12,28] although for some very light rotors such as H 3 + with much larger rotational energy spacing, two rotational temperatures had been derived. [29] Although the calculated electric dipole moments have been used in the calculations, the optimized microwave pulse widths for the transitions observed suggest that the calculated electric dipole moment components are consistent with the experimental data.…”

“…This is the first high resolution study of a chiral contact pair with two different permanently chiral molecules. Only three high-resolution spectroscopic studies of Gly-containing complexes, that is, Gly···H 2 O, [13] Gly···Gly, [12] and Gly···NH 3 , [14] have been reported so far, and only one or two conformers were detected in each case. Gly has two major monomeric conformers, with one being about four times more abundant than the other at room temperature.…”

“…[35] Interestingly, in the case of Gly···Gly, only two homochiral conformers were detected, although extensive searches had been carried out for several other Gly···Gly conformers which were predicted to have similar stability. [12] If the formation of the Gly···PO complex is a purely kinetically controlled process, one would expect binary conformers containing gÀG + to be more than four times more abundant than those with g + GÀ in a Neon expansion. This is clearly not the case here since Homo IV of gÀG + is not observed despite considerable experimental efforts, while Hetero III, Homo II and Homo III of g + GÀ were all detected.…”