Canadian Journal of Chemistry p. 2069 - 2082 (1999)
Update date:2022-08-02
Topics:
Cozens, Frances L.
Kanagasabapathy
McClelland, Robert A.
Steenken, Steen
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 <20 ns) to be observed. When generated in HFIP, phenethyl cations can be seen to react with unphotolyzed styrene, giving rise to dimer cations that are observed to grow in as the initial phenethyl cation decays. The dimer cations, in common with the oligomer cations seen in cationic styrene polymerization, have a κ(max) 15-20 nm higher than the monomer and react with both solvent and styrene several orders of magnitude more slowly. This stabilization relative to the phenethyl may reflect an interaction with the aryl group present at the λ-carbon. Cations 4-MeOC6H4C+(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.
View MoreBeijing Mediking Biopharm Co., Ltd.
Contact:+86-10-89753524/81760121/81769521
Address:Hongxianghong Incubator, Beiqijia Town, Changping district, Beijing, China
Anhui Biochem United Pharmaceutical Co., Ltd.
Contact:0086 551 5167062 / 5228268
Address:No. 30 Hongfeng Road, Hi-Tech Development Zone, Hefei (230088), China
Neworld Chemical Co., Ltd Shanghai(expird)
Contact:+86-21-62202658
Address:11F, Blvd 2, No. 1969 PuXing Rd, Shanghai
Hefei EnliPharma Tecnology Co.,Ltd
Contact:0086-551-66399836
Address:Qing Cheng ShuiXiang Building 805, Mengcheng North Road , ShuangFeng Economic Development Zone Anhui HeFei
Qingdao Pana-Life Biochem Co.,Ltd.
Contact:86-532-87683902
Address:No.967 Dalao Road, Licang Zone, Qingdao City,Shandong, China 266021
Doi:10.1134/S1070428014020092
(2014)Doi:10.1021/jo00110a001
(1995)Doi:10.1002/chem.202004951
(2021)Doi:10.1021/ja964271e
(1997)Doi:10.1021/cg500327s
(2014)Doi:10.5560/ZNB.2014-4016
(2014)