| Abstract
| - In this report, we describe rotational spectroscopic and high-level ab initio studies of the 1:1chiral molecular adduct of propylene oxide dimer. The complexes are bound by weak secondary hydrogenbonds, that is, the Oepoxy···H−C noncovalent interactions. Six homochiral and six heterochiral conformerswere predicted to be the most stable configurations where each monomer acts as a proton acceptor anda donor simultaneously, forming two six- or five-membered intermolecular hydrogen-bonded rings. Rotationalspectra of six, that is, three homochiral and heterochiral conformer pairs, out of the eight conformers thatwere predicted to have sufficiently large permanent electric dipole moments were measured and analyzed.The relative conformational stability order and the signs of the chiral recognition energies of the sixconformers were determined experimentally and were compared to the ab initio computational results.The experimental observations and the ab initio calculations suggest that the concerted effort of theseweak secondary hydrogen bonds can successfully lock the subunits in a particular orientation and that theoverall binding strength is comparable to a classic hydrogen bond.
|
