State-specific Enrichment of Chiral Conformers with Microwave Spectroscopy

TL;DR

This paper demonstrates the first experimental enantiomeric enrichment of chiral conformers using microwave three-wave mixing, showing potential for analytical and fundamental studies of molecules without stereogenic centers.

Contribution

It introduces a novel microwave spectroscopy method for enantiomeric enrichment of chiral conformers, expanding the scope of chiral analysis beyond stereogenic centers.

Findings

Achieved enantiomeric excess in chiral conformers via microwave three-wave mixing.

First experimental demonstration of enantiomeric enrichment in conformers without stereogenic centers.

Showcased broad applicability of three-wave mixing for fundamental and analytical purposes.

Abstract

An interesting class of molecules is that in which the molecules do not possess a stereogenic center but can become chiral due to their spatial arrangement. These molecules can be seen as chiral conformers, whose two non-superimposable forms can interconvert from one another by rotations about single bonds. Here, we show that an initially racemic mixture of chiral conformers, such as a sample of cyclohexylmethanol, C$_{7}$H$_{14}$O (CHM), can be enantiomerically enriched by performing the enantio-selective process of coherent population transfer between rotational levels. By first performing a population transfer cycle, followed by a three-wave mixing experiment, we show that an enantiomeric excess in a rotational level of choice can be achieved. This represents the first experimental demonstration of such an effect in a chiral pair of conformers, and it showcases the broad applicability of three-wave mixing not only for analytical applications but also to a wide scope of experiments of fundamental interest.