PROFESSOR EMERITUS(O)
B.S. University of California, Berkeley, 1953
PhD. University of Colorado, 1958
Professor Freeman's research presently involves studies of the mechanisms of photochemical transformation of substrates that are of environmental significance or are useful models for key environmental molecular components. He is also investigating the photochemistry of polyhaloarenes in organized media and rearrangements of bivalent carbon intermediates.
In recent studies, evidence has been revealed that photochemical transformations of polyhaloarenes, in the presence or absence of electron donors, involves radical anion species (I, either complexed or uncomplexed) as product determining intermediates. Elucidating the nature of the process leading to radical anion I and the mechanistic pathway for product formation from I will provide the background for understanding a class of reaction of key importance in environmental chemistry, especially in regard to those reactions of importance to human health. Evidence for the formation of I is obtained through the evaluation of the
dependence of quantum yield upon substrate concentration, electron donor concentration, solvent polarity and the presence of sensitisers and quenchers. Evidence bearing on the fragmentation of I is derived by evaluating the regiochemistry of the process for a particular substrate, analyses of fragmentation patterns of neutral parents of I in negative ion chemical ionization mass spectral runs, and molecular orbital analyses.
The photochemistry of polyhaloarene substrates in aqueous micellar media offers the opportunity to assess the efficiency of the photohydrodehalogenation process with electron donor present in the same micelle, separated from the substrate in the micelle by the Stern layer, or completely absent from the micelle and the local environment. The dependence of the quantum yield upon the presence of oxygen will provide important insight into applications of the photohydrodehalogenation reaction to toxic waste disposal. The regiochemistry of the process under each of these conditions will reveal the effect of complexation (I closely associated with a radical cation) upon the fragmentation pathway of the radical anion.
Reactions involving carbene to carbene rearrangements under study may be illustrated by the cycloalkylcarbene rearrangement illustrated in the equation above (II _ III). Electronic reorganization analogous to the degenerate rearrangement of ethynylcarbene results in ring cleavage and rearrangement to an alkynylcarbene. Calculations of DG°298 for this series suggests that the rearrangement should be studied in the forward direction in the case of the cyclopropenyl system and in the reverse direction in the case of the larger cycloalkenyl systems. Competition by hydrogen migration in the latter cases might be a problem, although (a) substitution of carbonyl for methylene at C-2, (b) gem dimethyl substitution at C-2 and (c) generation of the carbene in the triplet state are reasonable solutions.
PROFESSOR EMERITUS(O)
B.S. University of California, Berkeley, 1953
PhD. University of Colorado, 1958
Professor Freeman's research presently involves studies of the mechanisms of photochemical transformation of substrates that are of environmental significance or are useful models for key environmental molecular components. He is also investigating the photochemistry of polyhaloarenes in organized media and rearrangements of bivalent carbon intermediates.
In recent studies, evidence has been revealed that photochemical transformations of polyhaloarenes, in the presence or absence of electron donors, involves radical anion species (I, either complexed or uncomplexed) as product determining intermediates. Elucidating the nature of the process leading to radical anion I and the mechanistic pathway for product formation from I will provide the background for understanding a class of reaction of key importance in environmental chemistry, especially in regard to those reactions of importance to human health. Evidence for the formation of I is obtained through the evaluation of the
dependence of quantum yield upon substrate concentration, electron donor concentration, solvent polarity and the presence of sensitisers and quenchers. Evidence bearing on the fragmentation of I is derived by evaluating the regiochemistry of the process for a particular substrate, analyses of fragmentation patterns of neutral parents of I in negative ion chemical ionization mass spectral runs, and molecular orbital analyses.
The photochemistry of polyhaloarene substrates in aqueous micellar media offers the opportunity to assess the efficiency of the photohydrodehalogenation process with electron donor present in the same micelle, separated from the substrate in the micelle by the Stern layer, or completely absent from the micelle and the local environment. The dependence of the quantum yield upon the presence of oxygen will provide important insight into applications of the photohydrodehalogenation reaction to toxic waste disposal. The regiochemistry of the process under each of these conditions will reveal the effect of complexation (I closely associated with a radical cation) upon the fragmentation pathway of the radical anion.
Reactions involving carbene to carbene rearrangements under study may be illustrated by the cycloalkylcarbene rearrangement illustrated in the equation above (II _ III). Electronic reorganization analogous to the degenerate rearrangement of ethynylcarbene results in ring cleavage and rearrangement to an alkynylcarbene. Calculations of DG°298 for this series suggests that the rearrangement should be studied in the forward direction in the case of the cyclopropenyl system and in the reverse direction in the case of the larger cycloalkenyl systems. Competition by hydrogen migration in the latter cases might be a problem, although (a) substitution of carbonyl for methylene at C-2, (b) gem dimethyl substitution at C-2 and (c) generation of the carbene in the triplet state are reasonable solutions.