The Elusive Benzocyclobutenylidene: A Combined Computational and Experimental Attempt
摘要:
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 tripler 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 azibenzocycllobutene (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). C-13-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 [C-13]-3 and excellent agreement between observed and calculated isotopic shifts. Prolonged short-wavelength irradiation converts 3 into benzocyclobutadiene (5). Phenylacetylene (6) and benzocyclo- butadiene dimer (11) were identified as products arising from flash vacuum pyrolysis of diazirine 10 at 500 degreesC.
The Elusive Benzocyclobutenylidene: A Combined Computational and Experimental Attempt
摘要:
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 tripler 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 azibenzocycllobutene (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). C-13-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 [C-13]-3 and excellent agreement between observed and calculated isotopic shifts. Prolonged short-wavelength irradiation converts 3 into benzocyclobutadiene (5). Phenylacetylene (6) and benzocyclo- butadiene dimer (11) were identified as products arising from flash vacuum pyrolysis of diazirine 10 at 500 degreesC.
C8H6 Thermal Chemistry. 7-Methylenecyclohepta-1,3,5-dienyne (Heptafulvyne) by Flash Vacuum Thermolysis–Matrix Isolation. Chemical Activation in the Rearrangements of Phenylenedicarbenes and of Benzocyclobutadiene to Phenylacetylene
compound 2 as observed by IR spectroscopy and on-line mass spectrometry. FVT of 8 at 600–800°C causes rearrangement of 11 to phenylacetylene 12 and benzocyclobutadiene 13. Mechanisms for the rearrangements are proposed. Facile rearrangement of benzocyclobutadiene to phenylacetylene is ascribed to chemical activation, which is also seen to be involved in the rearrangement of p-, m-, and o-phenylenebiscarbenes
The Elusive Benzocyclobutenylidene: A Combined Computational and Experimental Attempt
作者:Athanassios Nicolaides、Takeshi Matsushita、Kohichi Yonezawa、Shinji Sawai、Hideo Tomioka、Louise L. Stracener、Jonathan A. Hodges、Robert J. McMahon
DOI:10.1021/ja0039482
日期:2001.3.1
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 tripler 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 azibenzocycllobutene (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). C-13-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 [C-13]-3 and excellent agreement between observed and calculated isotopic shifts. Prolonged short-wavelength irradiation converts 3 into benzocyclobutadiene (5). Phenylacetylene (6) and benzocyclo- butadiene dimer (11) were identified as products arising from flash vacuum pyrolysis of diazirine 10 at 500 degreesC.