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Titolo:
Remarkable kinetic stability of alpha-thiocarbamoyl substituted 4-methoxybenzyl cations
Autore:
McClelland, RA; Licence, VE; Richard, JP; Williams, KB; Lin, SS;
Indirizzi:
Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada Univ Toronto TorontoON Canada M5S 3H6 Chem, Toronto, ON M5S 3H6, Canada SUNY Buffalo, Dept Chem, Buffalo, NY 14260 USA SUNY Buffalo Buffalo NY USA 14260 ffalo, Dept Chem, Buffalo, NY 14260 USA
Titolo Testata:
CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE
fascicolo: 12, volume: 76, anno: 1998,
pagine: 1910 - 1915
SICI:
0008-4042(199812)76:12<1910:RKSOAS>2.0.ZU;2-M
Fonte:
ISI
Lingua:
ENG
Soggetto:
FLASH-PHOTOLYSIS GENERATION; ELIMINATION-REACTIONS; DIARYLMETHYL CATIONS; AZIDE ION; CARBOCATIONS; REACTIVITIES; TRIARYLMETHYL; LIFETIMES; ALKENE;
Keywords:
flash photolysis; thiocarbamoyl stabilized carbocation; photosolvolysis;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
18
Recensione:
Indirizzi per estratti:
Indirizzo: McClelland, RA Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada Univ Toronto Toronto ON Canada M5S 3H6 ON M5S 3H6, Canada
Citazione:
R.A. McClelland et al., "Remarkable kinetic stability of alpha-thiocarbamoyl substituted 4-methoxybenzyl cations", CAN J CHEM, 76(12), 1998, pp. 1910-1915

Abstract

4-Methoxybenzyl cations bearing alpha-(N,N-dimethylcarbamoyl) and alpha-(N,N-dimethylthiocarbamoyl) substituents have been generated photochemically upon irradiation of precursors with pentafluorobenzoate or 4-methoxybenzoate leaving groups. The ions have been observed with flash photolysis in 40:60 acetonitrile:water and in 50:50 methanol:water, and rate constants were measured for their decay in solvent alone and for their capture by azide ion. The cations so studied and their lifetimes in 40% acetonitrile are 6, ArCH-CONMe2, 0.6 mu s; 2, ArC+H-CSNMe2, 7 ms; and 4, ArC+(CH3)-CSMe2. 6 ms, where Ar = 4-MeOC6H4. The cation 4 reacts with solvent by elimination of a proton from the a-methyl group, and the rate constant for solvent addition must be less than l s(-1). The CSNMe2 substituted cations are 10(5)-10(7)-fold longer lived than analogs where the thioamide group has been replaced with an alpha-methyl. The UV-visible absorption spectra of these two cations also show significant differences from those of typical 4-methoxybenzyl cations. Thus, both the lifetimes and spectra point to a strong interaction ofthe benzylic centre with the thioamide group.

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Documento generato il 03/07/20 alle ore 01:08:00