Title page for ETD etd-050505-094910

Document Type dissertation

Author Name Laohhasurayotin, Somchoke

URN etd-050505-094910

Title Vapor phase photochemistry of cyanopyridines and pyridine. Deuterium labeling studies

Degree PhD

Department Chemistry & 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/Defense 2005-04-28

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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Document Type	dissertation
Author Name	Laohhasurayotin, Somchoke
URN	etd-050505-094910
Title	Vapor phase photochemistry of cyanopyridines and pyridine. Deuterium labeling studies
Degree	PhD
Department	Chemistry & 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/Defense	2005-04-28
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