STRUCTURAL INFORMATION FROM METHYL ROTORS - METHYL TORSIONAL BARRIERSIN P-HYDROXY-P'-METHYL-T-STILBENE AND ITS WATER COMPLEXES

The barriers to internal rotation for the methyl group in p-hydroxy-p' -methyl-t-stilbene and its one- and two-water complexes are reported. The jet-cooled fluorescence excitation spectra of these species are al so presented. The excitation spectrum of both p-hydroxy-t-stilbene and p-hydroxy-p'-methyl-t-stilbene exhibits two origins separated by simi lar to 270 cm(-1), which are due to the syn and anti conformers of the hydroxy group. The frequency difference between the two conformers ch anges dramatically in the water complexes. Additionally, barriers to i nternal rotation show a strong water complex dependence, changing by a s much as 25% with hydrogen bonding at the hydroxy group, a site 12 at oms away from the methyl rotor.