Photochemistry and photophysics of methylindenes and methyl-1,2-dihydronaphthalenes. (Volumes I and II)
Abstract
The photophysical and photochemical properties of methylindenes and methyl-1,2-dihydronaphthalenes in the gas phase have been studied. The results show that two electronic excited states, S$\sb{1}$ and S$\sb{2}$, are available to these compounds at excitation wavelengths greater than 220 nm. The S$\sb{2}$ states are non-emissive, a fact attributable to rapid radiationless decay processes in both compounds. The S$\sb{1}$ states of these compounds are weakly emissive. The mechanisms responsible for the photochemical methyl migrations of methylindenes in the gas phase were studied using the $\sp{13}$C-labelled methylindeness, 1-$\sp{13}$C-2-MI and 3-$\sp{13}$C-3-MI. Photolysis of these compounds at 254 nm in the gas phase produced rearranged products that can only be explained by detachment of the methyl group and re-attachment at another ring position. The proposed mechanism is a stepwise (1, 2) migration via diradical intermediates. Evidence was also obtained for extensive secondary photochemistry of the methylindenes upon prolonged photolysis in the gas phase. Two homologs of the methylindenes, 3-methyl-1,2-dihydronaphthalene and 4-methyl-1,2-dihydronaphthalene, were found to give gas phase photochemistry different from that observed in solution, and extensive studies in both phases are reported. These compounds undergo hydrogen shifts in the gas phase as well as a minor amount of methyl migration. Another major reaction pathway, in both solution and the gas phase, is electrocyclic ring opening of the cyclohexadienyl ring. Novel effects of added butane on the product distribution for 4-methyl-1,2-dihydronaphthalene are reported. Naphthalene, which is a formal methane elimination product, is also formed upon photolysis of either substrate, apparently as a consequence of secondary photochemistry.
Degree
Ph.D.
Advisors
Morrison, Purdue University.
Subject Area
Organic chemistry
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