Engel, Paul S.2009-06-042009-06-041991Culotta, 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>.https://hdl.handle.net/1911/16434The 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.241 p.application/pdfengCopyright 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.Organic chemistryPhysical chemistryThesisThesis Chem. 1991 Culotta