| Abstract
| - Isomer formation in dimeric complexes of a chiralnaphthalene derivative (2-naphthyl-1-ethanol) withnonchiralor chiral primary and secondary alcohols (n-propanol,2-methyl-1-butanol, 2-butanol, 2-pentanol) has beenstudied by hole-burning spectroscopy. Besides the spectroscopicdiscrimination between the homochiral andheterochiral complexes, previously observed in the fluorescenceexcitation spectra, ground-state depletionexperiments have shown that each diastereoisomer is cooled in the jetin several isomeric forms. To getinformation on the structures of the complexes and on the influence ofthe solvent conformations of thesestructures, semiempirical calculations that rely on the exchangeperturbation method have been performed.It has been shown that the most stable complexes involve a H-bondbetween the chromophore acting as thedonor and the solvent and that they involve anti and gaucheconformations of the solvent. The bindingenergy of the complexes results from a subtle balance betweenelectrostatic and dispersive forces: the complexesinvolving the gauche and anti conformers of the solvent differ fromeach other by the amount of dispersionenergy relative to the total interaction energy. The increase inthe dispersive forces calculated for the complexeswith the anti conformers has been related to a larger red shift of theabsorption spectrum and is suggested toplay a role in the observed chiral discrimination.
|
