Nanosecond kinetic absorption and calorimetric studies of cyclopentenone: the triplet, self-quenching, and the predimerization biradicals.
The photolysis of 2-cyclopentenone has been studied by a combination of kinetic absorption spectrophotometry and time-resolved photoacoustic calorimetry. The lifetime of the cyclopentenone triplet is strongly concentration dependent and corresponds to a value of 380 +/- 75 ns at infinite dilution in acetonitrile. The biradical intermediate (or pair of isomeric biradicals) immediately preceding formation of photodimer forms with very high efficiency upon quenching of triplet cyclopentenone by a second ground state cyclopentenone molecule and has an energy of 47 kcal/mol relative to two molecules of reactant. Quenching of the cyclopentenone triplet by conjugated dienes is much slower than expected, which is the reason that early estimates of the triplet lifetime were much too short.
Caldwell
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Programs in Chemistry, University of Texas at Dallas, Richardson 75080.
Tang
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Schuster
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Heibel
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D002151:Calorimetry; D003517:Cyclopentanes / Q000737:chemistry*; D005609:Free Radicals; D007700:Kinetics; D010782:Photolysis; D013997:Time Factors
D003517:Cyclopentanes; D005609:Free Radicals; C013905:cyclopentenone