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The Effect of Temperature on Competing Photochemical Hydrogen Abstraction Reactions in the Solid State
Author(s) -
Greenhough Trevor J.,
Scheffer John R.,
Secco Anthony S.,
Trotter James,
Walsh Leueen
Publication year - 1985
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198500047
Subject(s) - chemistry , hydrogen atom abstraction , hydrogen , photochemistry , hydrogen atom , intramolecular force , excited state , oxygen , carbon fibers , activation energy , computational chemistry , stereochemistry , atomic physics , organic chemistry , alkyl , physics , materials science , composite number , composite material
Irradiation of 4aα,5,8,8aα‐tetrahydronaphthoquin‐1‐on‐4 β ‐o1 (1a) and its 6,7‐dimethyl derivative 1b in the solid state leads to two products. The first is formed via intramolecular hydrogen abstraction by carbonyl oxygen followed by radical coupling, and the second is produced through initial hydrogen abstraction by enone carbon and subsequent radical coupling. X‐ray crystallography reveals that both processes are topochemically allowed, and the geometric parameters for the hydrogen transfers and the radical coupling reactions are tabulated. In the case of 1b, the photoproduct ratio was found to be temperature dependent with hydrogen atom abstraction by carbon predominating at lower temperatures. From the slope of the linear plot of the natural logarithm of the photoproduct ratio versus the reciprocal of the temperature, an activation energy difference of approximately 4 kcal/mole is calculated. The results are interpreted as being due to competing reactions from ( n,π *) 3 and (π*) 3 excited states, the latter (hydrogen abstraction by carbon) having a lower activation energy than the former (hydrogen abstraction by oxygen).