62698-27-5Relevant academic research and scientific papers
Gas-phase ion-molecule reaction of alpha-phenylvinyl cation towards substituted benzenes in the environment of an ITMS
Begala, Michela,Tocco, Graziella
experimental part, p. 1115 - 1124 (2012/02/03)
Ion-molecule reactions between the α-phenylvinyl cation (α-PVC) and mono-substituted benzenes have been investigated using a quadrople ion-trap mass spectrometer. The α-PVC, generated by chemical ionization from phenylacetilene, was found to react selectively with mono-substituted benzenes bearing electron withdrawing groups to give the product ions [M + 103] + and the trans-vinylating product ions [M + 25]+. To characterize the reaction products, a combination of collision-induced dissociation, isotope-labeling experiments and model compounds were used. The results indicate, in addition to direct heteroatom alkylation, high extent of ortho attack. We attributed the positional selectivity of the α-PVC to the nature of the substituent on the neutral molecule. In particular, hydroxy and amino groups promoted the alkenylation at ortho position. Copyright
Lifetimes and UV-visible absorption spectra of benzyl, phenethyl, and cumyl carbocations and corresponding vinyl cations. A laser flash photolysis study
Cozens, Frances L.,Kanagasabapathy,McClelland, Robert A.,Steenken, Steen
, p. 2069 - 2082 (2007/10/03)
Benzyl (4-MeO, 4-Me, and 4-methoxy-1-naphthylmethyl), phenethyl (4- Me2N, 4-MeO, 3,4-(MeO)2, 4-Me, 3-Me, 4-F, 3-MeO, 2,6-Me2, parent, and 4- methoxy-1-naphthylethyl) and cumyl (4-Me2N, 4-MeO, 4-Me, parent) cations have been studied by laser flash photolysis (LFP) in 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). In most cases styrene or α-methylstyrene precursors were employed for the phenethyl and cumyl ions, the intermediate being obtained by solvent protonation of the excited state. Benzyl cations were generated by photoheterolysis of trimethylammonium and chloride precursors. While a 4-MeO substituent provides sufficient stabilization to permit observation of cations in TFE, cations with less stabilizing substituents usually require the less nucleophilic HFIP. Even in this solvent, the parent benzyl cation is too short-lived (lifetime 6H4C+(R)-CH3 (R = Me, Et, i-Pr, t-Bu, cyclopropyl, C6H5, 4-MeOC6H4) were generated in TFE via the photoprotonation route. The alkyl series shows that steric effects are important in the decay reaction. The cation with R = cyclopropyl is a factor of 1.5 less reactive than the cation where R = phenyl. Several vinyl cations have also been generated by photoprotonation of phenylacetylenes. ArC+=CH2 has a reactivity very similar to that of its analog ArC+H-CH3, the vinyl cation being slightly (factors of 2-5) shorter-lived. For the various series of cations, including vinyl, substituents in the aryl ring have a consistent effect on the κ(max), a shift to higher wavelength relative to hydrogen of 15 nm for 4-Me, 30 nm for 4-MeO, and 50 nm for 4-Me2N.
Selectivity in the Reactions of Less Stable Carbocations with Magnesium Halides in Aprotic Solvents. A Theoretical Approach to the Constant Selectivity Principle.
Martinez, A. Garcia,Alvarez, R. Martinez,Vilar E. Teso,Fraile, A. Garcia,Barcina, J. Osio,Subramanian, L. R.
, p. 7077 - 7084 (2007/10/02)
The solvolysis of 7,7-bis(trifluoromethylsulfonyloxy)-2-norbornene (1a), 1-trifluoromethylsulfonyloxy-1-phenylethylene (2a), 2-methyl-1-cyclohexen-1-yl triflate (3a) and 4-camphenyl triflate (4a) in carbon disulfide or diethyl ether with added MgI2 and MgBr2 yields a mixture of the corresponding halides 5b-e, 6b-c, 7b-c and 8b-c.The ionization of the triflate group is favoured by coordination with the magnesium halide.The reaction with MgI2 was found to be second-order and is about 50 times more reactive than MgBr2.The selectivities of the intermediate cations 5-8 toward the nucleophiles MgI2 and MgBr2 are nearly constant, although the solvolysis rates differ by more than three powers of ten.A theoretical explanation of the constant selectivity principle is given.
