Jazmin Marlinga - University of Victoria

Placement: National Research Council of Canada
Supervisor: Dr. Linda Johnston

Generation and Characterization of Diarylpentenol Radical Cations and Their Photocyclized Products via Laser Flash Photolysis

To date, relatively little is known about photoinduced cyclizations and the mechanisms of intramolecular trapping. However, these types of reactions are growing in importance due to their increased synthetic utility (i.e. commercial production of lactones, etc.). Herein lies the impetus in recording such key data as lifetimes and decay and quenching rates to develop a firm mechanistic basis for the use of radical ion cyclization chemistry in synthesis and other biologically important reactions.

In this study, the radical cation intermediate of 5,5-diphenylpent-4-en-1-ol will be generated and characterized by laser flash photolysis techniques. The induction of photocyclization and the mechanism for product formation has been well documented. The measured first order rate constant for the disappearance of the transient presumably corresponds to the cyclization step and provides one of the first calibrations of an intramolecular trapping rate for a functionalized olefin. Competitive quenching studies will also be performed (namely with methanol and other anionic nucleophiles) to further discern the radical cation reactivity and its propensity for intramolecular nucleophile trapping.

Preliminary experiments have demonstrated a quick trapping rate, or short lifetime of this radical cation on the nanosecond timescale. To better resolve its kinetics, other methods will be employed, such as low temperature studies, and the use of an anisyl derivative whose methoxy substituents should provide additional stability thus allowing the transient to persist. Product studies with the anisyl analog will be carried out to parallel those previously performed with the phenyl compound.

Comparative experiments with simple 1,1-diarylethylenes may give some indication of the alkyl chain contribution towards transient reactivity. Additionally, studies in different solvents of varying polarity will be examined to record the relative efficiencies of these photoinduced processes. A 9,10-dicyanoanthracene (DCA) sensitizer system with biphenyl cosensitizer will be used to conduct all experiments.