ACID AND BASE CATALYZED PHOTOREACTIONS

The first part of this Thesis is a study of the photohydrations of a number of aromatic alkenes and alkynes in aqueous sulfuric acid. It was found that only certain aromatic alkenes and alkynes undergo clean photohydration. The substrates which did not display efficient photohydration may be divided into two classes: those compounds with electron withdrawing groups in S(,1), and those possessing a weak carbon-halogen bond elsewhere in the molecule.;A structure-reactivity relationship study was carried out for those aromatic alkenes which photohydrate cleanly from S(,1). It was found that electron donating or withdrawing abilities of substituents in S(,1) do not generally reflect their ground state sigma ((sigma)) values. For example, the meta fluoro group is strongly electron withdrawing ((sigma)('+) = 0.35) in the ground state but evidence presented in this work suggests it is much less electron withdrawing--or in fact even becomes electron donating--in S(,1). The opposite appears to be true for the para fluoro substituent.;The photohydrations of the non-nitro-substituted aromatic alkenes can be water, hydronium ion or general acid-catalyzed. The observation of general acid-catalysis supports the proposed mechanism involving product-forming protonation of S(,1) for these substrates. The individual catalytic rate constants for photoprotonation obey the Bronsted catalysis law, with an (alpha) value of ca. 0.15, suggesting early transition states in these photoprotonations.;The second part of this Thesis is a study of a set of reactions (which are termed photoredox reactions) of nitroaromatic benzyl alcohols discovered during the course of the study on the photohydration of m-nitro-phenylacetylene. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.;Three different photohydration mechanisms were discovered. This is in contrast to the (ground state) thermal hydration of aromatic alkenes and alkynes, which are all known to hydrate via rate-limiting protonation at the (beta)-carbon of the alkene or alkyne moiety, to give Markovnikov addition products. For the non-nitro-substituted aromatic alkenes and alkynes, the proposed photohydration mechanism involves a product-forming protonation step on S(,1), while for the nitrostyrenes, a product-forming attack of water on T(,1) at the (beta)-carbon (to give the anti-Markovnikov addition product) is consistent with the available data. A mechanism involving a concerted addition of H(,3)O('+) to T(,1) (to give the anti-Markovnikov addition product) is proposed for the photohydration of the nitrophenylacetylenes.