CONFORMATIONAL ANALYSIS OF GUAIAZULENE IN ITS GROUND AND SECOND EXCITED SINGLET STATE
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Date
1985
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Publisher
Ohio State University
Abstract
The fluorescence excitation spectrum of jet-cooled guaiazulene (1, 4-dimethyl-7-isopropylazulene, I, has been studied in the $0=2200 cm^{-1}$ region of the $S_{2} \leftarrow S_{o}$ electronic transition. Two spectroscopic origins have been observed at 27483 and $27589 cm^{-1}$, corresponding to the two stable conformations of the isopropyl group. The ground-state energy difference for the two rotamers was measured by two different temperature-dependence studies: changing nozzle temperature and changing X/D, the distance between the nozzle and the laser. These two experiments consistently yield a ground-state energy difference of $0.9 \pm 0.3 cm^{-1}$, and give indirect evidence for a low barrier to internal rotation. The relative stabilities of the two rotamers reverse in the $S_{2}$ excited electronic state, and their energy difference is much larger, about $105 cm^{-1}$. [FIGURE].
Description
Author Institution: Department of Chemistry, Tufts University; Department of Chemistry, Tufts University; Department of Chemistry, Tufts University