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Time‐resolved resonance Raman and density functional theory study of the photochemistry of 4‐benzoylpyridine in acetonitrile and 2‐propanol
Author(s) -
Du Yong,
Xue Jiadan,
Ma Chensheng,
Kwok Wai Ming,
Phillips David Lee
Publication year - 2008
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1869
Subject(s) - ketyl , chemistry , photochemistry , hydrogen atom abstraction , flash photolysis , benzophenone , triplet state , density functional theory , acetonitrile , solvent effects , ketene , radical , reaction rate constant , solvent , molecule , computational chemistry , medicinal chemistry , organic chemistry , physics , quantum mechanics , kinetics
A nanosecond time‐resolved resonance Raman (ns‐TR 3 ) spectroscopic investigation of the intermolecular hydrogen‐abstraction reaction of the triplet state of 4‐benzoylpyridine (4‐BPy) in 2‐propanol solvent is reported. The TR 3 results reveal a rapid hydrogen abstraction (<10 ns) by the 4‐BPy triplet state ( n π*) with the 2‐propanol solvent, leading to formation of a 4‐BPy ketyl radical and an associated dimethyl ketyl radical partner from the solvent. The recombination of these two radical species occurs with a time constant about 200 ns to produce a para ‐N‐LAT (light absorbing transient). The structure, major spectral features, and identification of the ketyl radical and the para ‐N‐LAT coupling complex have been determined and confirmed by comparison of the TR 3 results with results from density functional theory (DFT) calculations. A reaction pathway for the photolysis of 4‐BPy in 2‐propanol deduced from the TR 3 results is also presented. The electron‐withdrawing effect of the heterocyclic nitrogen for 4‐BPy on the triplet state makes it have a significantly higher chemical reactivity for the hydrogen abstraction with 2‐propanol compared to the previously reported corresponding benzophenone triplet reaction under similar reaction conditions. In addition, the 4‐BPy ketyl radical reacts with the dimethyl ketyl radical to attach at the para ‐N atom position of the pyridine ring to form a cross‐coupling product such as 2‐[4‐(hydroxy‐phenyl‐methylene)‐4h‐pyridin‐1‐yl]‐propan‐2‐ol instead of attacking at the para ‐C atom position as was observed for the corresponding benzophenone reaction reported in an earlier study. Copyright © 2008 John Wiley & Sons, Ltd.