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UBC Theses and Dissertations
Solution and crystalline state photochemistry of 2,3-diacyl-substituted benzobarrelenes Yap, Melvin Peng-Kwun
Abstract
A series of 2,3-diacyl-substituted benzobarrelenes was synthesized and their photochemistry investigated in the crystalline state and in solution media. The differences in photoreactivity and product selectivity between these compounds in the two phases were determined, and structure- reactivity correlations were established based on X-ray crystallographic data. The photochemistry of the title series is multiplicity-dependent; benzocyclooctatetraene is formed through the singlet excited state and benzosemibullvalenes are products of the triplet excited state. Regioisomeric benzosemibullvalenes are derived from the different "di-TT-me thane" rearrangement pathways taken. Solution phase, triplet-state photoisomerizations of a number of symmetrically disubstituted benzobarrelenes gave two benzosemibullvalenes1,2- disubstituted and 2a,6c-disubstituted. Selectivity is controlled predominantly by electronic effects. The use of a benzoyl substituent as one of the acyl groups enhances intersystem crossing, thereby enabling the substrate to achieve the triplet excited state through direct irradiation. Photolyses of several unsymmetrical benzoyl/ester benzobarrelenes in the solid state gave strikingly unusual regioselectivities between the 1,2-disubstituted and the 2a,5c-disubstituted products. The presence of specific lattice interactions was determined to be the major factor responsible; electronic effects were shown to play a much less significant role. Photochemical investigation of the benzoyl/methyl ester system was also conducted in polymer matrix media to show variation in product selectivity. Ammonium and metal ion salts of benzobarrelene-2,3-dicarboxylic acid were photolyzed in solution and the crystalline phase; their triplet product selectivities were recorded to further support the dominance of specific lattice interaction effects over electronic effects. Discovery of a rare "tri-TT-methane" rearrangement in some dibenzobarrelenes prompted the design and synthesis of dimethyl 1,4-dihydro1,4,5,8- tetramethyl-1,4-ethenonaphthalene-2,3-dicarboxylate. This successfully underwent the tri-TT-methane rearrangement in both solution and solid states. The novel selectivity was rationalized in terms of intramolecular steric effects rather than on the basis of electronic stabilizing effects. Many benzosemibullvalene photoproducts were found to undergo [1,3] shifts from a secondary photolysis; coincidentally, these rearrangements lead to regioisomeric benzosemibullvalenes. As a result, many exist in unusual photostationary states. It was found that benzosemibullvalenes require a carbonyl substituent adjacent to the bond cleaved in order for the [1,3] shift reaction to take place.
Item Metadata
Title |
Solution and crystalline state photochemistry of 2,3-diacyl-substituted benzobarrelenes
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1992
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Description |
A series of 2,3-diacyl-substituted benzobarrelenes was synthesized
and their photochemistry investigated in the crystalline state and in
solution media. The differences in photoreactivity and product selectivity
between these compounds in the two phases were determined, and structure-
reactivity correlations were established based on X-ray crystallographic
data.
The photochemistry of the title series is multiplicity-dependent;
benzocyclooctatetraene is formed through the singlet excited state
and benzosemibullvalenes are products of the triplet excited state.
Regioisomeric benzosemibullvalenes are derived from the different
"di-TT-me thane" rearrangement pathways taken.
Solution phase, triplet-state photoisomerizations of a number of
symmetrically disubstituted benzobarrelenes gave two benzosemibullvalenes1,2-
disubstituted and 2a,6c-disubstituted. Selectivity is controlled
predominantly by electronic effects.
The use of a benzoyl substituent as one of the acyl groups enhances
intersystem crossing, thereby enabling the substrate to achieve the
triplet excited state through direct irradiation. Photolyses of
several unsymmetrical benzoyl/ester benzobarrelenes in the solid state
gave strikingly unusual regioselectivities between the 1,2-disubstituted
and the 2a,5c-disubstituted products. The presence of specific lattice
interactions was determined to be the major factor responsible;
electronic effects were shown to play a much less significant role.
Photochemical investigation of the benzoyl/methyl ester system was
also conducted in polymer matrix media to show variation in product
selectivity.
Ammonium and metal ion salts of benzobarrelene-2,3-dicarboxylic acid
were photolyzed in solution and the crystalline phase; their triplet
product selectivities were recorded to further support the dominance of
specific lattice interaction effects over electronic effects.
Discovery of a rare "tri-TT-methane" rearrangement in some dibenzobarrelenes
prompted the design and synthesis of dimethyl 1,4-dihydro1,4,5,8-
tetramethyl-1,4-ethenonaphthalene-2,3-dicarboxylate. This
successfully underwent the tri-TT-methane rearrangement in both solution
and solid states. The novel selectivity was rationalized in terms of
intramolecular steric effects rather than on the basis of electronic
stabilizing effects.
Many benzosemibullvalene photoproducts were found to undergo
[1,3] shifts from a secondary photolysis; coincidentally, these
rearrangements lead to regioisomeric benzosemibullvalenes. As a result,
many exist in unusual photostationary states. It was found that
benzosemibullvalenes require a carbonyl substituent adjacent to the
bond cleaved in order for the [1,3] shift reaction to take place.
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Extent |
8337853 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-01-08
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0061743
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1992-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.