Singlet biradicals of the 3,4-dimethyleneheterocycle series, where the heterocycle is furan, thiophene, or N-substituted pyrrole, with chromophores in the UV-vis region (560-640 nm), are generated by nanosecond laser flash photolysis of diazene precursors in fluid solution. The rate constants for disappearance of these transients are determined by time-resolved absorption spectroscopy using the long-wavelength band. The rate constants for dimerization are near the encounter-controlled rate. Rates of trapping by alkenes are well described by a frontier orbital model. Oxygen trapping rate constants range between 10(7) and 10(9) M-1 s-1. The ratios of rate constants for trapping of 3,4-dimethylene-N-(p-toluenesulfonyl)pyrrole by pairs of alkenes in preparative competition experiments are in good agreement with those determined by the flash photolytic method. This confirms assignments of the 3,4-dimethyleneheterocycle structure to the chromophore of the biradical transients.
Parallel reactivity sequences in cycloadditions of singlet biradicals and Diels-Alder reactions. A common physical basis manifested as entropy control or enthalpy control
作者:J. C. Scaiano、Veronique Wintgens、Karl Haider、Jerome A. Berson
DOI:10.1021/ja00205a032
日期:1989.11
Reactivite des diradicaux dimethyl-3,4 furanne et dimethyl-3,4 thiophene, generes a partir des diazenes correspondants, vis-a-vis de divers composes vinyliques
Reactive des diradicaux dimethyl-3,4 furanne et dimethyl-3,4 thiophene,generes a partir des diazenes 通讯员,vis-a-vis de divers composesvinyliques
Absolute rates of dimerization and cycloaddition of 3,4-dimethylenefuran and 3,4-dimethylenethiophene by nanosecond time-resolved spectroscopy
作者:J. C. Scaiano、Veronique. Wintgens、Ann. Bedell、Jerome A. Berson
DOI:10.1021/ja00220a061
日期:1988.6
3,4-Dimethylenefuran and 3,4-dimethylenethiophene, heterocyclic analogs of the disjoint non-Kekule hydrocarbon tetramethyleneethane
作者:Keith J. Stone、Marc M. Greenberg、Joshua L. Goodman、Kevin S. Peters、Jerome A. Berson
DOI:10.1021/ja00285a035
日期:1986.12
Ground-state multiplicities of 3,4-dimethylenefuran and 3,4-dimethylenethiophene. Experimental tests of ab initio and semiempirical theories of heteroatom-bridged disjoint biradicals
作者:Marc M. Greenberg、Silas C. Blackstock、Keith J. Stone、Jerome A. Berson
DOI:10.1021/ja00192a026
日期:1989.5
Absolute rates of heterocyclic singlet biradical reactions determined by nanosecond time-resolved absorption spectroscopy. Dimerizations and cycloadditions to alkenes and to dioxygen
作者:Richard B. Heath、Linda C. Busch、Xu Wu Feng、Jerome A. Berson、J. C. Scaiano、Alain B. Berinstain
DOI:10.1021/j100152a047
日期:1993.12
Singlet biradicals of the 3,4-dimethyleneheterocycle series, where the heterocycle is furan, thiophene, or N-substituted pyrrole, with chromophores in the UV-vis region (560-640 nm), are generated by nanosecond laser flash photolysis of diazene precursors in fluid solution. The rate constants for disappearance of these transients are determined by time-resolved absorption spectroscopy using the long-wavelength band. The rate constants for dimerization are near the encounter-controlled rate. Rates of trapping by alkenes are well described by a frontier orbital model. Oxygen trapping rate constants range between 10(7) and 10(9) M-1 s-1. The ratios of rate constants for trapping of 3,4-dimethylene-N-(p-toluenesulfonyl)pyrrole by pairs of alkenes in preparative competition experiments are in good agreement with those determined by the flash photolytic method. This confirms assignments of the 3,4-dimethyleneheterocycle structure to the chromophore of the biradical transients.