Graduate Thesis Or Dissertation

 

The photochemistry of some insect juvenile hormone analogs Public Deposited

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  • The photochemistry of some analogs of insect growth regulators (IGR's) was studied. Methyl geranate, TY, was synthesized and the mechanisms of its photochemical reaction pathways were studied by a variety of techniques. Direct irradiation of 71 in ether leads to the formation of five new products: 98, the product of a [1,3] sigmatropic shift; 72, a bicyclo[2.1.1]hexane derivative; 73, a cylclopentane derivative; 100, the product of in-chain deconjugation to the Z isomer; and 97, the product of isomerization about the C-2 bond. Irradiation in the presence of propiophenone as a triplet sensitizer lead to the formation of only 72, 73 and 97, identifying them as arising from the triplet excited state. Irradiation of 71 in ether with varying amounts of base lead to the formation of (in addition to products already mentioned) 99 and 100, the other two possible deconjugation products. Examination of Scheme 29 leads to the derivation of the kinetic rate expressions in Scheme 31, and plotting the ratios of 99/73, 100/73 and 101/73 yields values for the relative rate of [1,5] sigmatropic shift of hydrogen from a photodienol species (119, 121, 123) to regenerate starting esters (71, 97) rather than going on to deconjugation products (99, 100, 101). It was found that the relative rates of sigmatropic shift for 119 and 123 were nearly identical but 121 was about 75 times slower. This decrease in the relative rate for 121 is ascribed to the extra steric repulsion in 121, causing it to adopt the unreactive s-trans conformation and thus slowing the reaction. Insect juvenile hormone, 74, was synthesized and irradiated in ether and was found to undergo photochemical processes similar to that of 71. The primary photoprocess is isomerizatrion about the C-2 and C-6 double bonds. Isomerization about the C-6 bond was unexpected and indicated the intermediacy of an exciplex. To study the role of exciplexes in the E/Z isomerizartion of isolated double bonds in the juvenile hormone, 74, the unsymmetrically terminated analog 92 and the dihydro analog 93 were synthesized. Irradiation of 92 and 93 in solvents of varying polarity (ET) lead to an increase of the quantum yield of E/Z isomerization for both 92 and 93, indicating the intermediacy of an intermolecular exciplex. to study the role of intramolecular exciplexes 92 and 93 were irradiated in ether at increasing dilution (0.1 M - 0.0008 M). It was found that the intermolecular exciplex is the major contributor in the concentration range studied without any evidence for an intramolecular exciplex.
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