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Time‐Resolved Resonance Raman and Density Functional Study of an Azirine Intermediate in the 2‐Fluorenylnitrene Ring‐Expansion Reaction To Form a Dehydroazepine Product
Author(s) -
Ong Shing Yau,
Zhu Peizhi,
Leung King Hung,
Phillips David Lee
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200390157
Subject(s) - azirine , raman spectroscopy , ring (chemistry) , chemistry , resonance (particle physics) , photochemistry , atomic physics , physics , optics , organic chemistry
Abstract We report time‐resolved resonance Raman spectra for the azirine intermediate produced in the 2‐fluorenylnitrene ring‐expansion reaction to form a dehydroazepine product. The Raman bands obtained with a 252.7 nm probe wavelength and 500 ns delay time exhibit reasonable agreement with predicted vibrational frequencies from density functional calculations for two isomers of azirine intermediates that may be formed from a 2‐fluorenylnitrene precursor. The Raman bands observed for delay times of 15 ns and 10 μs were consistent with predicted vibrational frequencies from density functional calculations for the 2‐fluorenylnitrene and dehydroazepine product species as well as previously reported 416 nm time‐resolved Raman spectra obtained on the ns and μs time scales. Our results demonstrate that the 2‐fluorenylnitrene ring‐expansion reaction to produce dehydroazepine products proceeds via relatively long‐lived 2‐fluorenylnitrene and azirine intermediates. Substitution of a phenyl ring para to the nitrene group of phenylnitrene appears to lead to significant changes in the ring‐expansion reaction so that longer lived arylnitrene and azirine intermediates can be observed. This should enable the chemical reactivity of azirine intermediates formed from arylnitrenes to be examined more readily.