Worcester Polytechnic Institute Electronic Theses and Dissertations Collection

Title page for ETD etd-050505-094910


Document Typedissertation
Author NameLaohhasurayotin, Somchoke
URNetd-050505-094910
TitleVapor phase photochemistry of cyanopyridines and pyridine. Deuterium labeling studies
DegreePhD
DepartmentChemistry & Biochemistry
Advisors
  • Professor James W. Pavlik, Advisor
  • Professor W. Grant McGimpsey, Committee Member
  • Professor Venkat R. Thalladi, Committee Member
  • Professor Richard P. Johnson, Committee Member
  • Keywords
  • cyanopyridine
  • methylpyridine
  • pyridine
  • phototransposition
  • azaprefulvene
  • deuterium labeling
  • Date of Presentation/Defense2005-04-28
    Availability unrestricted

    Abstract

    The vapor phase photochemistry of the three isomeric cyanopyridines and the three methylpyridines was studied by irradiating their vapors at 254 nm. It was found that direct irradiation of any one cyanopyridine isomer resulted in the formation of the other two isomers of cyanopyridine or methylpyridines respectively. The reactivity of each isomer was found to be different. This was suggested to be based on the stability of their azaprefulvene intermediates formed during interconversion. The phototransposition of these molecules was suggested to result from 2,6-bonding, nitrogen migration around the five sides of cyclopentenyl ring followed by rearomatization. This mechanism was found to be consistent with the results of deuterium labeling studies of cyanopyridines These result suggest that cyanopyridines undergo phototransposition via the intermediacy of azaprefulvenes instead of Dewar-pyridine and azaprismane.

    Thus, photochemical studies showed that the six trideuteriopyridine isomers constitute two separate photochemical triads. Each triad consists of three isomers that are photointerconverting upon irradiation at 254 nm in the vapor phase. Similary, it was found that the three isomeric tetradeuteriopyridine isomers also constitute a photochemical triad and are interconverting upon irradiation at 254 nm in the vapor phase. These phototranspositions are best explained by the cyclization, nitrogen migration, and rearomatization mechanism. These results are in contrast to the long-held belief that pyridine is photostable in the vapor phase. Instead, unlabeled pyridine undergoes a hidden phototransposition leading back to itself.

    Files
  • Laohhasurayotin.pdf

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