Methyl-Group Move in Low-Temperature Rare-Gas Matrixes and Conformational Analysis of 1,4-Dimethoxybenzene

Abstract

Conformational changes of 1,4-dimethoxybenzene in low-temperature rare-gas matrixes have been investigated by FTIR spectroscopy with an aid of the density-functional-theory calculation. Two stable conformers, cis-planar and trans-planar, are found to exist in argon matrixes by comparing the observed spectrum with the calculated spectral patterns. The enthalpy difference between the conformers is estimated from the dependence in the population ratio on the nozzle temperature to be 1.12 ± 0.09 kJ mol-1, where cis is more stable than trans. On the other hand, cis changes to trans in krypton and xenon matrixes in dark, in contrast to the stability in the argon matrix. The conversion rate constants are estimated from the decay behavior of a cis band at various matrix temperatures. Dependence of the rate constants on the matrix temperature is found to be inconsistent with the Arrhenius law. The conformational changes in krypton and xenon matrixes are ascribed to the torsional potential changes caused by an inte...