Lam, Ernest Yee Yeung (1968) I. Photodimerization of cyclohexenone II. Radiation chemistry of benzophenone in cyclohexene solution. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-02092009-140344
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PART I: The photodimerization of cyclohexenone has been studied in the neat liquid and in solvents. Although four products can be detected, 1 and 2 predominate under all conditions. The reaction can be sensitized by benzophenone, thioxanthone, acetophenone, and naphthalene. The enone was used as a sensitizer for the cis- trans isomerization of three pairs of isomeric olefins and the response was used to estimate the triplet excitation energy of the enone as 61 ± 1 kcal per mole. Dimerization can be quenched by addition of piperylene. Most evidence points to a triplet mechanism for the reaction. However, the ratio of 1 to 2 varies with reaction conditions and the quantum yield does not show the expected variation with enone concentration. These phenomena are attributed to solvent effects, rather than to a change of mechanism.
PART II: Gamma-irradiation of benzophenone in cyclohexene solution produced 3,3'-dicyclohexenyl and cyclohexenyldiphenylcarbinol as main products. The reaction was quenched by phenyl disulfide and to a less extent by chloroform. It was not significantly affected by 2-propanol. Naphthalene also acted as a quencher. The reaction probably involved the cleavage of the allylic C-H bond of cyclohexene to a cyclohexenyl radical and a hydrogen atom. Benzophenone effectively took up the hydrogen atom to give a ketyl radical. The main cross product, cyclohexenyldiphenylcarbinol, resulted from a combination of the ketyl radical with the cyclohexenyl radical.
Quenching by naphthalene was taken to be an indication that excited states of cyclohexene played an important role, probably as a precursor of cyclohexenyl radical. This was supported by the fact that gamma-irradiation or cis- or trans-2,3-diphenylpropenes in cyclohexene solution resulted in isomerization. That benzophenone did not act as an energy sink in cyclohexene was probably due to inefficient energy transfer from an excited cyclohexene triplet to benzophenone.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||20 September 1967|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||11 Feb 2009|
|Last Modified:||26 Dec 2012 02:30|
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