Infrared Studies on the Less Stable Conformer of Isoprene in Argon Matrices

In frared spectra of the less stable conformer of isoprene have been observed in low-temperature argon matrices (Figs 1-3). Irradiation of the matrix-isolated isoprene with a low-pressure Hg lamp increases the population of the less stable conformer. Deposition of an isoprene/argon mixture heated through a high temperature nozzle exhibits a similar effect. The less stable conformer has been identified as the gauche form by comparing the observed spectra with the results of normal-coordinate calculations previously reported by Bock et al. Most of the observed bands in the region below 1700 cm^-1 have been reasonably assigned to the calculated modes of either the trans or the gauche form (Table 1).