Cis–trans isomerization equilibrium in hydroquinone in low-temperature argon and xenon matrices studied by FTIR spectroscopy

Torsional isomerization between cis and trans hydroquinone in low-temperature matrices has been studied by FTIR spectroscopy with an aid of DFT calculations. When the temperature of Xe matrix was changed between 16 and 75 K, the cis/trans population ratio changed reversibly in conformance with the Boltzmann distribution law, despite the high torsional barrier, 10.8 kJ mol−1. The cis–trans enthalpy difference was estimated from the population changes to be 0.19±0.06 kJ mol−1. The cis–trans isomerization equilibrium at low temperature is accounted for in terms of the matrix-induced tunneling of hydrogen atoms.