Hydrogen‐Atom Tunneling in a Homochiral Environment

Abstract

The role‐exchanging concerted torsional motion of two hydrogen atoms in the homochiral dimer of trans‐1,2‐cyclohexanediol was characterized through a combination of broadband rotational spectroscopy and theoretical modeling. The results reveal that the concerted tunneling motion of the hydrogen atoms leads to the inversion of the sign of the dipole moment components along the a and b principal axes, due to the interchange motion that cooperatively breaks and reforms one intermolecular hydrogen bond. This motion is also coupled with two acceptor switching motions. The energy difference between the two ground vibrational states arising from this tunneling motion was determined to be 29.003(2) MHz. The corresponding wavefunctions suggest that the two hydrogen atoms are evenly delocalized on two equivalent potential wells, which differs from the heterochiral case where the hydrogen atoms are confined in separate wells, as the permutation‐inversion symmetry breaks down. This intriguing contrast in hydrogen‐atom behavior between homochiral and heterochiral environments could further illuminate our understanding of the role of chirality in intermolecular interactions and dynamics.

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

“…The recently observed tunneling splitting present in one of the homo dimers of trans -CD should not be of concern for cis -PCD given the large structural changes relative to trans -CD that do not readily allow for a conversion between equivalent conformers. 64 The homochiral preference observed for cold cis -PCD contrasts to what was observed in trans -CD and cis -CD for which the predicted heterochiral preference is explained by the formation of an outstandingly stable heterochiral dimer that optimises the number of possible hydrogen bonds via a quadruple insertion structure. Due to the strong similarities between cis -CD and trans -CD, it is clear that the changes in clustering propensity of cis -PCD are due to the presence of the phenyl substituent rather than the consequences of cis-trans isomerism.…”