Photochemistry of phenyl alkyl ketones. The lifetime of the intermediate biradicals
The lifetimes of a number of biradicals produced in the photochemical Norrish type II reaction of phenyl alkyl ketones have been measured. The decay of the biradicals was followed by monitoring the competition with electron transfer to paraquat dications using nanosecond laser techniques. The lifetimes are rather insensitive to changes in temperature, substitution, and solvent, and are typically in the neighborhood of 100 ns. It is concluded that intersystem crossing is the main factor determining the biradical lifetimes. The rate constant for electron transfer to paraquat dications is 3.7 x 10/sup 9/ M/sup -1/s/sup -1/ in methanol at room temperature for 1,4-ketyl--alkyl biradicals, and considerably higher for diketyl biradicals, apparently reflecting a change in path degeneracy. Oxygen behaves as a biradical scavenger with a rate constant of 6.2 x 10/sup 9/ M/sup -1/s/sup -1/ in methanol. The lifetimes of the excited ketone triplets have also been determined at room temperature under the experimental conditions employed; this is an important parameter in determining the viability of the measurements of biradical lifetimes by this technique.
- Research Organization:
- Univ. of Notre Dame, IN
- OSTI ID:
- 5190129
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 81:22; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
Similar Records
Role of biradical intermediates in the photochemistry of o-methylacetophenone
Differentiation of excited-state and biradical processes. Photochemistry of phenyl alkyl ketones in the presence of oxygen