Carbanion mechanisms XXI. Solution acidity of triphenylsilane
Comparative acidity measurements have been performed between triphenylsilylpotassium and a series of arylmethanes by 1H-NMR in tetrahydrofuran: Ph3SiK + ArnCH4 - n ? Ph3SiH + ArnCH3 - nK Metalation of the arylmethane was complete in the case of Ph3CH (pKa 31.4) and Ph2CH2 (pKa 33.4) but with (p-CH3·C6H4)2CH2 (pKa 35.1) ~50% metalation of the di-p-tolymethane occurred, indicating that the two acids have equal pKa. No reaction occurred with 4-Ph·C6H4·CH3 (pKa 38.7). Thus pKa Ph3SiH ≈ 35.1 in THF. This represents the first solution measurement of the acidity of an organosilane.
Buncel, Erwin,Venkatachalam
p. 208 - 210
(2007/10/03)
METAL-STABILIZED CARBANIONS VI. FORMATION OF SOME ARYLMETHYL AND DIBENZOTROPENYL CARBANIONS COMPLEXED WITH TRICARBONYLCHROMIUM. A KINETIC AND A 13C NMR STUDY
Rate constants have been measured for the α-metallation of some arylmethanes, of 5H-dibenzocycloheptene and its dihydro derivative, free and complexed with tricarbonylchromium, by potassium hydride in tetrahydrofuran in the presence of 18-crown-6 ether.The stable solutions of the complexed anions have been studied by 13C NMR spectroscopy.With the free ligands the kinetic acidity depends upon the structure to a great extent, but in the corresponding complexes the rates of metallation do not vary appreciably.On the basis of the 13C chemical shift data a close similarity is suggested between the electronic structures of the arylmethyl and dibenzotropenyl anions which would account for their very similar metallation rates.
Ceccon, Alberto,Gambaro, Alessandro,Venzo, Alfonso
p. 209 - 222
(2007/10/02)
EQUILIBRIUM CH ACIDITY OF ARYLACETYLENES IN DIMETHYL SULFOXIDE
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Terekhova, M. I.,Petrov, E. S.,Vasilevskii, S. F.,Ivanov, V. F.,Shvartsberg, M. S.
p. 850 - 852
(2007/10/02)
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