title: Time-resolved resonance Raman and density functional study of an azirine intermediate in the 2-fluorenylnitrene ring-expansion reaction to form a dehydroazepine product.
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 micros 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 micros 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.
authors.affiliation: Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong S.A.R., People's Republic of China.
authors.forename: Shing Yau
authors.initials: SY
authors.lastname: Ong
authors.forename: Peizhi
authors.initials: P
authors.lastname: Zhu
authors.forename: King Hung
authors.initials: KH
authors.lastname: Leung
authors.forename: David Lee
authors.initials: DL
authors.lastname: Phillips