Cole, Ronald Sinclair (1968) Part I. Photodimerizations of Coumarin. Part II. Asymmetric induction during energy transfer. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-01222008-114929
Abstract
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Part I:
Studies on the mechanism of the photodimerizations of coumarin are reported. Trans coumarin photodimers are shown to result from excited triplet coumarin. It seems likely that an intermediate triplet-ground state complex precedes a biradical intermediate which closes to trans-dicoumarin. This dimer, formedby benzophenone sensitization is also produced by direct irradiation in benzene. Here coumarin has a low intersystem crossing yield of [...]. We account for 98% of the absorbed quanta by a photocleavage of coumarin singlets, competing with the other modes of unimolecular decay. No evidence supporting singlet self quenching was found. Singlet energy transfer from benzophenone to coumarin occurs by emission-reabsorption. The low efficiency of the latter process makes it insignificant compared to competing mechanisms.
Part II:
Studies on the detailed mechanism of an energy transfer are reported. Optically active photosensitizers induce optical activity into trans-1,2-diphenylcyclopropane, II, while effecting the trans [...] cis isomerization. The asymmetric induction is shown to result from differing rates of energy transfer to the two optical isomer of trans-II. A rather large steric effect operative during energy transfer is thus demonstrated. Quenching studies indicate that the reaction occurs by a singlet mechanism resulting in production of 1,3 -diphenyltrimethylene. The intermediate apparently has the same decays paths as that generated by triplet energy transfer to II. The asymmetric induction results from a number of sensitizers are useful in constructing a probable transition state for this energy transfer reaction.
Item Type: | Thesis (Dissertation (Ph.D.)) |
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Degree Grantor: | California Institute of Technology |
Major Option: | Chemistry |
Thesis Committee: |
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Defense Date: | 20 June 1967 |
Record Number: | etd-01222008-114929 |
Persistent URL: | http://resolver.caltech.edu/CaltechETD:etd-01222008-114929 |
Default Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. |
ID Code: | 278 |
Collection: | CaltechTHESES |
Deposited By: | Imported from ETD-db |
Deposited On: | 22 Jan 2008 |
Last Modified: | 25 Dec 2012 14:58 |
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