76898-65-2Relevant academic research and scientific papers
Comparative study of the pyrolysis, photoinduced electron transfer (PET), and laser-jet and 185-nm photochemistry of alkyl-substituted bicyclic azoalkanes
Adam, Waldmar,Denninger, Uwe,Finzel, Ralf,Kita, Fumio,Platsch, Herbert,Walter, Herbert,Zang, Gerald
, p. 5027 - 5035 (2007/10/02)
The gas-phase pyrolysis, photoinduccd electron transfer (PET), and laser-jet 185-nm photochemistry of 2,3-diazabicyclo[2.2.1]hept-2-ene (1a), syn-7-methyl-2,3-diazabicyclo[2.2.1]hept-2-ene (syn-1b), anti-7-methyl-2,3-diazabicyclo[2.2.1]hept-2-ene (anti-1b), 1,4-dimethyl-2,3-diazabicyclo[2.2.1]hept-2-ene (1c), 7,7-dimethyl-2,3-diazabicyclo[2.2.1]hept-2-ene (1d), syn-7-(1-methylethyl)-2,3-diazabicyclo[2.2.2]hept-2-ene (syn-1e) were investigated and the results of their product studies compared with one another. Pyrolysis and conventional direct and benzophenone-sensitized 350-nm photolysis of the azoalkanes 1 yielded the bicyclo[2.1.0]pentanes 2 and negligible amounts of cyclopentenes 3. PET and benzophenone-sensitized laser-jet and 185-nm photolysis of the azoalkanes 1 led to significant quantities of cyclopentene derivatives 3, a bekavior that is attributed to radical cation-type 1,3-cyclopentadiyl intermediates, which subsequently suffer hydrogen or alkyl migration. The polar character of the radial cation D?+ is clearly demonstrated by the Wagner-Meerwein rearrangement into 2,3-dimethylcyclopentene (3′d) in the PET and 185-nm photolysis of azoalkane 1d. When the corresponding 1,3-cyclopentadiyl D?? was generated in the pyrolysis of 5,5-dimethylbicyclo[2.1.0]pentane (2d), the 3,3-dimethyl-1,4-pentadiene (4d) was obtained as the exclusive reaction product; instead of methyl migration, fragmentation into the 1,4-diene took place. The PET chemistry of the stereochemically labeled azoalkanes syn- and anti-1b revealed that the radical cations D?+ have a puckered geometry, because a stereochemical memory effect was observed for the cyclopentene products 3. Specifically, the pseudoaxial substituent at the stereolabled center migrates with preference, which speaks for a coplanar arrangement for the rearrangement in D?+. The common and distinct mechanistic features of the denitrogenation process of the various thermal and photochemical activation modes will be discussed.
Photochemical and ESR spectral evidence for a stereoselective rearrangement of radical cations derived from azoalkanes and bicyclopentanes
Adam, Waldemar,Walter, Herbert,Chen, Guo-Fei,Williams, Ffrancon
, p. 3007 - 3014 (2007/10/02)
Studies of the photosensitized electron transfer (PET) reactions of anti/syn-5-methylbicyclo[2.1.0]pentane (1a,b) and syn/anti-7-methyl-2,3-diazabicyclo[2.2.1]hept-2-ene (2a,b) have revealed a remarkable stereochemical memory effect. Thus, 1a and 2a furnished only 1-methylcyclopentene (3a) as the rearrangement product, while their isomers 1b and 2b afforded predominantly 3-methylcyclopentene (3b). The pathway responsible for the stereoselective olefin formation can be assigned to a radical cation rearrangement. This was established on the basis of direct ESR evidence showing that the 1,3-diyl radical cations 1a,b?+ detected initially at 80-90 K following the radiolytic oxidation of 1a,b in CF3CCl3 rearranged stereoselectively into the olefin radical cations 3a,b?+ at 105 K. The ESR results further establish that, in the puckered conformations of 1a,b?+, the pseudo-axial substituent on the methylene bridge is in almost perfect coplanar alignment with the radical cation 2p orbital lobes, thus facilitating its stereoselective migration. Also, in agreement with PET results, matrix ESR studies demonstrated that, on radiolytic oxidation of the azoalkanes 2a,b, the olefin radical cations 3a,b?+ were formed with high selectivity, although no precursor radical cations were detected in this case.
Kinetics of the Thermal Skeletal Inversion of Bicyclopentane and Methylbicyclopentanes
Baldwin, John E.,Ollerenshaw, James
, p. 2116 - 2119 (2007/10/02)
cis-exo-2,3-Dideuteriobicyclopentane, cis-exo-2,3-dideuterio-1-methylbicyclopentane, and the endo and exo isomers of 5-methylbicyclopentane have been prepared; rate constants for the gas-phase equilibrations between these substrates and the corresponding ring-inverted isomers have been determined between 153 and 208 deg C.The parent hydrocarbon and 1-methylbicyclopentane have equal or nearly equal activation energies, 37.8 +/- 0.1 and 38.0 +/- 0.4 kcal/mol; the 2-methyl and 5-methyl systems have slightly higher Ea values, 38.7 to 39.2 kcal/mol.These data and related information from the literature are assessed in terms of electronic and steric substituent effects on ground-state bicyclopentanes and transition states leading to planar 1,3-cyclopentadiyl diradicals.
