| THE SPECTROSCOPY AND PHOTOPHYSICS OF 2-, 4- AND 5-METHYLPYRIMIDINE. (1991) | |||||||||
Abstract | |||||||||
| Author Institution: Department of Chemistry, Purdue University. A spectroscopic study of the effect of the position of methyl substitution on the photophysics of methylpyrimidines has been carried out. Of particular interest is the effect the substitution position has on the barrier to internal rotation. Laser-induced fluorescence excitation was used to probe the $S_{1}$ states of jet-cooled 4-, 5- and 2-methylpyrimidine. The $S_{0}$ state was probed using dispersed fluorescence. In the case of 5-m-p, assignments could readily be made via comparison with the spectroscopy of unsubstituted pyrimidine. Furthermore, a nearly free rotor is seen in both $S_{0}$ and $S_{1}$. With the reduction in symmetry in 4-m-p, we see a 100 $cm^{-1}$ barrier in $S_{0}$ with a 7-fold increase upon going to $S_{1}$. In addition, the spectroscopic influence of the methyl group is more prevalent in 4-m-p than in 5-m-p. It appears at the present time that 2-m-p exhibits much the same spectroscopy as seen in 5-m-p, particularly with respect to internal rotation. | |||||||||
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