The photochemistry of azocyclopropanes

dc.contributor.advisorEngel, Paul S.en_US
dc.creatorBodager, Gregory Allenen_US
dc.date.accessioned2009-06-04T00:03:45Zen_US
dc.date.available2009-06-04T00:03:45Zen_US
dc.date.issued1988en_US
dc.description.abstractThe photochemistry of a number of azocyclopropanes has been studied: cis-1-(methyl-trans-azo)-2-phenylcyclopropane, trans-10(methyl-trans-azo)-2-phenylcyclopropane, trans-azocyclopropane and cis-azocyclopropane. Direct irradiation into the lowest n $\rightarrow\pi$* band led to nearly exclusive cis-trans isomerization of the azo group. Minor processes for the phenylcyclopropanes were cyclopropyl ring isomerization, rig expansion of 1-methyl-5-phenyl-2-pyrazoline and formation of styrene. These processes suggest formation of a biradical intermediate which is apparently not formed in the case of trans- and cis-azocyclopropane. Singlet sensitization of cis-1-(methyl-trans-azo)-2-phenylcyclopropane with benzene increased the quantum yields of the processes competing with azo group isomerization. The increased efficiencies indicate that the second excited state of the azoalkane contributed to the observed photochemistry. On the other hand, the second excited state of trans- and cis-azocyclopropane is not accessible to benzene singlet sensitization and so led to exclusive interconversion of the two azo isomers. Direct irradiation into the short wavelength UV band of trans- and cis-azocyclopropane in pentane produced more decomposition products than n $\rightarrow\pi$* excitation. The efficiency of trans $\rightarrow$ cis azo group isomerization decreased at the expense of the C-N and cyclopropyl C-C homolyses. These two cleavages accounted for a large number of products including nitrogen, cyclopropane, ethylene and 1-cyclopropyl-2-pyrazoline. Cyclopropyl ring cleavage to a biradical intermediate followed by reclosure to regenerate the starting azoalkane was postulated as one of the major processes to rationalize the low quantum yield of products. Formation of products propene, allylcyclopropane and 1,5-hexadience upon irradiation at 193 nm suggested production of vibrationally excited cyclopropyl radicals which rearrange to allyl. Short wavelength irradiation of trans-azocyclopropane in the vapor phase led to a large number of decomposition products. Triplet-sensitization of cis-1-(methyl-trans-azo)-2-phenylcyclopropane produced both azo and cyclopropyl group isomerization products, but not styrene. The differing product distribution relative to direct irradiation indicates that the triplet state is not exclusively involved in the singlet photochemistry. The unusually high quantum yield found for triplet-sensitized isomerization of trans-azocyclopropane to the cis isomer was initially rationalized in terms of cyclopropyl ring cleavage to form a biradical intermediate. However, a stereospecifically labelled deuterium analog of trans-azocyclopropane, prepared to test the biradical hypothesis, showed that a such an intermediate is probably not formed upon triplet sensitization.en_US
dc.format.extent224 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoThesis Chem. 1988 Bodageren_US
dc.identifier.citationBodager, Gregory Allen. "The photochemistry of azocyclopropanes." (1988) Diss., Rice University. <a href="https://hdl.handle.net/1911/16126">https://hdl.handle.net/1911/16126</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/16126en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectOrganic chemistryen_US
dc.titleThe photochemistry of azocyclopropanesen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentChemistryen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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