74975-64-7

Upstream product

• 40811-05-0 1-(4-methoxyphenyl)-2-methylprop-1-enyl bromide 

Downstream Products

• 53578-10-2 1-Methoxy-4-[2-methyl-1-(2,2,2-trifluoro-ethoxy)-propenyl]-benzene 

Relevant academic research and scientific papers

Why are vinyl cations sluggish electrophiles?

The kinetics of the reactions of the vinyl cations 2 [Ph2C=C+-(4-MeO-C6H4)] and 3 [Me2C=C+-(4-MeO-C6H4)] (generated by laser flash photolysis) with diverse nucleophile

Lifetimes and UV-visible absorption spectra of benzyl, phenethyl, and cumyl carbocations and corresponding vinyl cations. A laser flash photolysis study

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.

Photochemical Formation and Electrophilic Reactivities of Vinyl Cations. Influence of Substituents, Anionic Leaving Groups, Solvents, and Excitation Wavelength on Photoheterolysis and Photohomolysis of 1-(p-R-Phenyl)-2-(2,2'-biphenyldiyl)vinyl Halides

Using product analysis and time-resolved laser flash photolysis techniques, the photochemistry at λexc ca. 250 and 310 nm (exc = excitation) of 1-(p-R-phenyl)-2-(2,2'-biphenyldiyl)vinyl halides (R = H, Me, MeO) in methanol and acetonitrile at room temperature was studied.The title compounds undergo photoheterolysis and photohomolysis to give vinyl cations =C+- (carbenium ions) and vinyl radicals =C.-.The cation : radical ratio increases with electron-donating strength of the substituent R, H - - - -, indicating that the cleavage of the C-X bond to yield cation and halide anion proceeds, in the rate-determining step, by heterolysis and not by homolysis followed by electron transfer in the radical pair.The cation : radical ratio is solvent dependent: e.g., for the vinyl bromide with R = MeO and with λexc = 308 nm, in CH2Cl2 as solvent, only radical is observed, in comparison with only cation in the much more polar solvent acetonitrile.In acetonitrile-methanol mixtures, the absolute yields of both cation and radical go through a maximum as the methanol content is increased, however, the catio : radical ratio decreases continuously with increasing .For a particular R, the quantum yield for C-X bond cleavage is higher at ca. 250 than at ca. 310 nm.Also, the cation : radical ratio is wavelength-dependent: at λexc ca. 310 nm there is relatively more heterolysis than at λexc ca. 250 nm.Rate constants for reaction of the cations with nucleophiles were determined in acetonitrile.Those for reaction of the cation with R = MeO (lifetime in acetonitrile 7 μs) with anionic nucleophiles such as the halides are at the diffusion limit in this solvent, ca. 2 * 1010 M-1 s-1, whereas those for reaction with water, alcohols, and cyclic ethers are of the order 105-106 M-1 s-1.The less stabilized cation (R = Me) reacts with alcohols faster by the factor ca. 100, and it decays in acetonitrile ca. 100 times more rapidly.Also, 1-(p-R-phenyl)-2-dimehtylvinyl bromides (R = H, Me, MeO) were photolyzed in acetonitrile.In the case of R = MeO, the cation p-CH3O-C6H4-C+=CMe2 was seen (lifetime 770 ns), and its reactivity with alcohols (k values of 106-107 M-1 s-1) and halides (k values of 1010 M-1 s-1) was determined.The vinyl radicals =C.- react with O2 to yield vinylperoxyl radicals =C-O2. which have absorption maxima at ca. 390 nm.

Reactions of Substituted Vinyl Cations in Acetonitrile Solution as Studied by Flash Photolysis

Vinyl cations Ia(+), Ib(+), Ic(+) of the structure R'2C=C(+)R" (Ia(+): R' = R' = anisyl; Ib(+): R' = phenyl, R" = anisyl; Ic(+): R' = methyl, R" = anisyl) were generated by flash photolysis of corresponding bromides.Lifetime measurements yielded the following: substitution of aromatic groups in 2-position by methyl groups largely improved the electrophilicity of the vinyl cations.The nucleophilicity of typical compounds (ketone, ester, alcohol, olefin) was measured. - Keywords: Vinyl Bromide, Electrophilicity, Vinyl Cation, Flash Photolysis