Photolysis of azoalkanes. Reactions and kinetics of the 1-cyclopropyl-1,3-cyclopentanediyl biradical and 1-cyclopropylcyclopentyl radical

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dc.contributor.advisorEngel, Paul S.en_US
dc.creatorCulotta, Anne Marieen_US
dc.date.accessioned2009-06-04T00:35:52Zen_US
dc.date.available2009-06-04T00:35:52Zen_US
dc.date.issued1991en_US
dc.description.abstractThe 1-cyclopropylcyclopentyl radical (114a) and 1-cyclopropylcyclohexyl radical (114b) were generated in the presence of PhSH via 366 nm photolysis of azo-1-cyclopropylcyclopentane and azo-1-cyclopropylcyclohexane respectively. These radicals undergo cyclopropylcarbinyl (CPC) rearrangement to primary homoallylic radicals 115a and 115b, respectively, at rates of 1.45 $\times$ 10$\sp7$ s$\sp{-1}$ and 1.1 $\times$ 10$\sp7$ s$\sp{-1}$ based on competitive trapping with PhSH. These rates are 6-9 times slower than the parent CPC radical. E$\sb{\rm a}$ for 114a$\to$115a was found to be 7.0 kcal/mol and log A = 12.3. Deuterium labeling studies show that homoallylic radical 115a recloses to 114a with k$\sb{\rm rr}$ = 5.5 $\times$ 10$\sp4$ s$\sp{-1}$. Unsymmetrical triplet biradical 1-cyclopropyl-1,3-cyclopentanediyl (104T) is produced from the triplet sensitized photolysis of 1-cyclopropyl-2,3-diazabicyclo (2.2.1) hept-2-ene (123). Biradical 104T undergoes CPC rearrangement to a pair of 1,6-biradicals 105E and 105Z the latter of which undergoes rapid intramolecular disproportionation to Z-3-propylidenecyclopentene (108Z). On account of its geometry, 105E cannot lead directly to a stable product; hence, it recloses to 104T (k$\sb{\rm ra}$ = 1.2 $\times$ 10$\sp5$ s$\sp{-1}$) but interestingly, not to 104S. If the CPC rearrangement rate of 104T is taken as that of 114a, we calculate from the product distribution that the lifetime ($\tau$ = 1/k$\sb{\rm isc}$) of 104T is 59 ns. This figure is only one half the lifetime of the parent 1,3-cyclopentanediyl and is close to $\tau$ = 42 ns for 1,3-dimethyl-1,3-cyclopentanediyl, showing that the effect of the cyclopropyl group is similar to that of methyl. ISC of 104T displays linear Arrhenius behavior over 3.4-61.0$\sp\circ$C. Activation parameters for ISC of 104T were determined via competition with the CPC rearrangement and were found to be E$\sb{\rm a}$ (ISC) = 1.6 kcal/mol and log A = 8.4. Thus 104T is shown to be a ground state triplet and the low value of log A is characteristic of spin-forbidden ISC.en_US
dc.format.extent241 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoThesis Chem. 1991 Culottaen_US
dc.identifier.citationCulotta, Anne Marie. "Photolysis of azoalkanes. Reactions and kinetics of the 1-cyclopropyl-1,3-cyclopentanediyl biradical and 1-cyclopropylcyclopentyl radical." (1991) Diss., Rice University. <a href="https://hdl.handle.net/1911/16434">https://hdl.handle.net/1911/16434</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/16434en_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.subjectPhysical chemistryen_US
dc.titlePhotolysis of azoalkanes. Reactions and kinetics of the 1-cyclopropyl-1,3-cyclopentanediyl biradical and 1-cyclopropylcyclopentyl radicalen_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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