title: The elusive benzocyclobutenylidene: a combined computational and experimental attempt.
abstract: Ab initio and density functional theory calculations predict that benzocyclobutenylidene (1) has a singlet ground state in contrast to the parent phenylcarbene and many other simply substituted arylcarbenes. Calculations also predict that 1 should lie in a relatively deep potential well, while its triplet state is 14.5 kcal mol(-)(1) higher in energy. However, attempts to observe 1 directly by photolysis of two different nitrogenous precursors were not successful. Irradiation of diazobenzocyclobutene (7) (lambda > 534 nm or lambda > 300 nm) or azibenzocyclobutene (10) (lambda > 328 nm) in Ar matrixes at 10 K leads to the formation of the strained cycloalkyne 7-methylenecyclohepta-3,5-dien-1-yne (3). (13)C-Labeled 3 was also prepared in a similar manner. There is very good agreement between experimental IR spectra and computationally derived harmonic vibrational frequencies for 3 and [(13)C]-3 and excellent agreement between observed and calculated isotopic shifts. Prolonged short-wavelength irradiation converts 3 into benzocyclobutadiene (5). Phenylacetylene (6) and benzocyclobutadiene dimer (11) were identified as products arising from flash vacuum pyrolysis of diazirine 10 at 500 degrees C.
authors.affiliation: Chemistry Department for Materials, Faculty of Engineering, Mie University, Tsu, Mie 514-8507 Japan.
authors.forename: A
authors.initials: A
authors.lastname: Nicolaides
authors.forename: T
authors.initials: T
authors.lastname: Matsushita
authors.forename: K
authors.initials: K
authors.lastname: Yonezawa
authors.forename: S
authors.initials: S
authors.lastname: Sawai
authors.forename: H
authors.initials: H
authors.lastname: Tomioka
authors.forename: L L
authors.initials: LL
authors.lastname: Stracener
authors.forename: J A
authors.initials: JA
authors.lastname: Hodges
authors.forename: R J
authors.initials: RJ
authors.lastname: McMahon