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Titolo:
Energetics and mechanism of alkyl cleavage transition states: Relative gas-phase acidities of alkanes
Autore:
Wong, J; Sannes, KA; Johnson, CE; Brauman, JI;
Indirizzi:
Stanford Univ, Dept Chem, Stanford, CA 94305 USA Stanford Univ Stanford CA USA 94305 iv, Dept Chem, Stanford, CA 94305 USA
Titolo Testata:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
fascicolo: 44, volume: 122, anno: 2000,
pagine: 10878 - 10885
SICI:
0002-7863(20001108)122:44<10878:EAMOAC>2.0.ZU;2-O
Fonte:
ISI
Lingua:
ENG
Soggetto:
ION-CYCLOTRON RESONANCE; THERMOCHEMICAL DETERMINATIONS; UNIMOLECULAR DECOMPOSITIONS; UNSYMMETRICAL KETONES; ALKOXIDE ANIONS; KINETIC METHOD; NEGATIVE-IONS; ENERGY; FRAGMENTATION; DEPROTONATION;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Life Sciences
Physical, Chemical & Earth Sciences
Citazioni:
34
Recensione:
Indirizzi per estratti:
Indirizzo: Brauman, JI Stanford Univ, Dept Chem, Stanford, CA 94305 USA Stanford Univ Stanford CA USA 94305 m, Stanford, CA 94305 USA
Citazione:
J. Wong et al., "Energetics and mechanism of alkyl cleavage transition states: Relative gas-phase acidities of alkanes", J AM CHEM S, 122(44), 2000, pp. 10878-10885

Abstract

The product branching ratios from the infrared multiple-photon dissociation (IRMPD) of a series of tertiary alkoxides are examined and an overall order for the relative acidities of several alkyl groups is inferred. Comparison with the order of acidities derived from a similar silane system revealsan overall similarity, although small differences exist. A model system, the reaction of phenyltrimethylsilane plus hydroxide to give either benzene or methane, is studied more closely. Analysis of the energetics of the alkoxide system and the silane system using statistical reaction rate theory (RRK and RRKM) reveals differences between the mechanisms of decomposition for the systems. These discrepancies between the known, experimental product ratio and the energetics suggest that the transition state of pentacoordinate hydroxysilane anion decomposition has concerted, albeit polar character. Decomposition of the pentacoordinate adduct formed by the reaction of methoxide plus phenyltrimethylsilane is consistent with this suggestion. Caution should be used when inferring the relative acidities of alkyl groups fromkinetic methods when assumptions of the decomposition mechanism have not been validated.

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Documento generato il 07/07/20 alle ore 04:43:37