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

Abstract

Chirality recognition in the hydrogen-bonded glycidol···propylene oxide complex has been studied by using rotational spectroscopy and ab initio calculations. An extensive conformational search has been performed for this binary adduct at the MP2/6-311++G(d,p) level of theory and a total of 28 homo- and heterochiral conformers were identified. The eight binary conformers, built of the two dominant glycidol monomeric conformers, g-G+ and g+G-, were predicted to be the most stable ones. Jet-cooled rotational spectra of six out of the eight conformers were observed and unambiguously assigned for the first time. The experimental stability ordering has been obtained and compared with the ab initio predictions. The relative stability of the two dominant glycidol monomeric conformers is reversed in some cases when binding to propylene oxide. The contributions of monomeric energy, deformation energy, and binary intermolecular interaction energy to the relative stability of the binary conformers are discussed.

Chiral Discrimination by Vibrational Spectroscopy Utilizing Local Modes

“…Special emphasis will be laid on the characterization of all H‐bonds and their contributions to the complex stability. The most stable complex is the heterochiral form 10a , which agrees with the MP2 calculations of Xu and coworkers . The next most stable form is the homochiral complex 11a , with a Δ E value of 0.46 kcal/mol.…”

“…Xu and coworkers suggested the use of propylene oxide (PO) … glycidol (Gly) complexes (Fig. ) as simple lock‐and‐key models simulating drug receptor recognition and binding .…”

“…The strongest HB1 bond is found for 10b with ω a = 672 cm –1 whereas ω a values of 636 and 634 cm –1 are calculated for the most stable complexes 10a and 11a . Decisive is HB2, which has not been considered so far . The corresponding ω a values are 327 cm –1 for 10a and 324 cm –1 for 11a .…”

The Hydrogen Bond and Beyond: Perspectives for Rotational Investigations of Non‐Covalent Interactions

“…The predicted relative energies between homo‐ and heterochiral complexes (chirodiastaltic energy) are small (i.e., −0.16 to 1.28 kJ mol −1 for 2‐fluoroethanol⋅⋅⋅propylene oxide), pointing to a “limited selectivity” . Moreover, stereospecific relative energies are model dependent and not always reproducible with theory, underlining that “it is quite challenging to capture such subtle energy difference accurately with current ab initio methods” . Actually, inclusion of zero‐point energies or basis set superposition error (BSSE) corrections may change the stability order, as sub‐kJ mol −1 accuracy may be required .…”

Mass Spectrometry Study and Infrared Spectroscopy of the Complex Between Camphor and the Two Enantiomers of Protonated Alanine: The Role of Higher‐Energy Conformers in the Enantioselectivity of the Dissociation Rate Constants

“…Information gained from gas‐phase experiments allows isolating the contact pairs responsible from chiral discrimination and disentangling the specific interactions within the molecule/ligand complex from the contribution of the solvent. Attempts at obtaining data at the microscopic level are pursued both from the stability and spectroscopy points of view, for both neutral and ionic systems …”