Alan C. Weedon
Organic Chemistry and Photochemistry
Education
B.Sc., Ph.D., London
AWARDS
- Bucke Award
- Merck Frosst Award
RESEARCH
Our research program consists of several projects which explore the mechanisms and synthetic applications of the reactions of organic molecules induced by ultra-violet light. These projects make use of the wide range of expertise and instrumentation available in the Photochemistry Unit. The main areas which are active in our laboratory at this time are: Enone Photochemistry. Carbonyl compounds that are conjugated with double bonds exhibit a photochemistry characterised by rearrangement reactions and cycloaddition reactions. We have used these reactions extensively in syntheses of natural products and novel molecules and for the development of new and synthetically useful transformations. We have also been examiningthe mechanisms of some of these reactions using techniques such as steady state kinetics, quantum yield determination, product studies, flash photolysis, steady state and time resolved e.s.r. and fluorescence spectroscopy. Many of these reactions proceed via unstable intermediates which are formed from the excited states, such as cations, twisted alkenes and radicals. We have been developing new techniques for trapping these species so as to gain information about their rates of formation, structures, reactivity and lifetimes. Indole and Pyrrole Photochemistry. The indole and pyrrole ring systems are commonly encountered components in many biologically important molecules. They are relatively inert photochemically unless the nitrogen atom is substituted by an acyl group, in which case a rich photochemistry is observed. We have been exploring the mechanism and synthetic applications of this photochemistry. Photochemical Destruction of Environmental Pollutants One method of permanent removal of pollutants from the environment is their photolysis to innocuous products. We are exploring a process which involves the destruction of volatile organic molecules present as contaminants in air by irradiation of a catalyst with ultra-violet light. This work is being performed in conjunction with several industrial companies who are interested in treating polluted air in enclosed spaces (e.g. in buildings) and in decontaminating off-gases from air-stripping processes.
Photochemistry of Organic Compounds in Supercritical Media In this project we are exploring the use of supercritical fluids as media for photochemical reactions. Supercritical fluids act as low density solvents for organic compounds. For the photochemist they have two interesting properties. The dielectric constant, and hence polarity of the medium can be varied dramatically by changing the pressure and hence the density of the fluid. Rate constants for diffusion in the fluids are also much faster than in condensed media so that bimolecular processes can become more competitive with unimolecular excited state decay or reaction. We are probing how these properties can be used to control or change the photochemical reactivity of organic compounds.
PUBLICATIONS
- "The Photo-Fries Reaction of 1-Naphthyl Acetate in Supercritical Carbon Dioxide: Chemical Evidence for Solvent-Solute Clustering," D. Andrew and A.C. Weedon, J. Am. Chem. Soc. 117, 6132 (1995).
- "Determination of the Relative Rates of Formation, Fates and Structures of Triplet 1,4-Biradicals Generated in the Photochemical Cycloaddition Reactions of 2-Cyclopentenones with 2-Methylpropene," D. Andrew and A.C. Weedon, J. Am. Chem. Soc. 117, 5647 (1995).
- "Trapping of Triplet 1,4-Biradicals with Hydrogen Selenide in the Intramolecular Photochemical Cycloaddition Reaction of 3-(4'-Pentenyl)cycloalk-2-enones: Verification of the Rule of Five", D.J. Maradyn and A.C. Weedon, J. Am. Chem. Soc. 117, 5359 (1995).
- "Mechanistic Investigation of the Reaction between 2-Cyclopentenone and Polar Alkenes: Trapping of 1,4-Biradical Intermediates with Hydrogen Selenide," D. Andrew, D.J. Hastings and A.C. Weedon, J. Am. Chem. Soc. 116, 10870 (1994).
- "The Photochemical Cycloaddition Reaction of 2-Cyclohexenone with Alkenes: Trapping of Triplet 1,4-Biradical Intermediates with Hydrogen Selenide," D.J. Maradyn and A.C. Weedon, Tetrahedron Lett. 35, 8107 (1994).
