title: Time-resolved resonance Raman observation of the dimerization of didehydroazepines in solution.
abstract: Time-resolved resonance Raman (TR3) studies of the photochemistry of phenyl azide, 3-hyroxyphenyl azide, 3-methoxyphenyl azide and 3-nitrophenyl azide in acetonitrile:water solutions is reported. After photolysis of these four aryl azides in room temperature solutions, only one species was observed in the TR3 spectra for each azide, respectively at the probe wavelengths employed in the TR3 experiments. The species observed after photolysis of 3-nitrophenyl azide was assigned to 3,3'-dinitroazobenzene, an azo compound formed from the dimerization reaction of triplet 3-nitrophenylnitrene. In contrast, the species observed after photolysis of phenyl azide, 3-hydroxyphenyl azide and 3-methoxyphenyl azide were tentatively assigned to intermediates formed from the dimerization of didehydroazepines that are produced from the ring expansion reaction of the respective singlet arylnitrene. To our knowledge, this is the first time-resolved vibrational spectroscopic observation of the dimerization reaction of didehydroazepines in solution. In addition, these are the first resonance Raman spectra reported for dimers formed from didehydroazepines. We briefly discuss the structures, properties and chemical reactivity of the dimer species observed in the TR3 spectra and possible implications for the photochemistry of aryl azides.
authors.affiliation: Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong S.A.R., People's Republic of China.
authors.forename: Jiadan
authors.initials: J
authors.lastname: Xue
authors.forename: Yong
authors.initials: Y
authors.lastname: Du
authors.forename: Yung Ping
authors.initials: YP
authors.lastname: Chuang
authors.forename: David Lee
authors.initials: DL
authors.lastname: Phillips
authors.forename: Jin
authors.initials: J
authors.lastname: Wang
authors.forename: Calvin
authors.initials: C
authors.lastname: Luk
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Hadad
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Platz
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D001381:Azepines / Q000138:chemical synthesis / Q000737:chemistry* / Q000528:radiation effects; D001386:Azides / Q000737:chemistry / Q000528:radiation effects; D019281:Dimerization; D015394:Molecular Structure; D010777:Photochemistry; D010782:Photolysis; D012015:Reference Standards; D012996:Solutions / Q000737:chemistry; D013059:Spectrum Analysis, Raman / Q000379:methods* / Q000592:standards; D013997:Time Factors; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D000097:Acetonitriles; D001381:Azepines; D001386:Azides; D012996:Solutions; D014867:Water; C032159:acetonitrile