Alan C. Weedon
Professor
Vice-Provost for Policy, Planning and Faculty
B.Sc., Ph.D., London
Lab: CHB
209
Phone: (519) 661-2111 ext. 86346
Organic Chemistry and Photochemistry
Awards:
• Merck Frosst Award
Current Research Programs:
Current Research Programs 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.
Selected 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).
