- Ion pair acidities and aggregation of some amide and oxazoline enolates in THF
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Equilibrium lithium ion pair acidities at 25 °C have been determined in THF for the following acetamides: N,N-dimethyl-(4-biphenylyl)acetamide (1) (19.69), N,N-diethyl-(4-biphenylyl)acetamide (2) (20.30), N,N-dimethyl- diphenylacetamide (3) (20.76), N,N-diethyl-diphenylacetamide (4) (21.99), and 1-(diphenylmethylcarbonyl)pyrrolidine (5) (21.08). These acidity data compare well with those previously reported for the corresponding cesium enolates. Lithium and cesium ion pair acidities in THF are reported for two oxazolines: 2-(4-biphenylylmethyl)oxazoline (6) (Li, 21.53; Cs, 25.49) and (E)-(4S,5R)- 2-(4-biphenylylmethyl)-4-methoxymethyl-5-phenyloxazoline (7) (Li, 20.10; Cs 24.21). Studies of their acidities over a wide range of concentrations indicate that all of the lithium and cesium enolates of 1-7 are essentially monomeric at concentrations ranging from 10-3 to 10-4 M. Traces of dimer were detected for the lithium enolates of amides 1 and 2 and for the cesium enolate of oxazoline 6. Their dimerization constants (M-1) were found to be about 450, 200, and 150, respectively. All of the other lithium and cesium enolate probably form small amounts of dimer, but the dimerization constant of -1 is below the limit of precision of our spectroscopic method.
- Facchetti, Antonio,Streitwieser, Andrew
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p. 2281 - 2286
(2007/10/03)
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- Some stable substituted cycloheptatrienyl carbanions
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The reaction of some 7-substituted cycloheptatrienes with KNH2 in liquid ammonia is described.In several cases stable carbanions are formed.Their NMR spectra are consistent with a non-planar pentadienyl-like structure.A comparison of the 1H-NMR spectra of 10 and 11 shows the paratropic character of the cycloheptatrienyl anions.
- Zwaard, A. W.,Kloosterziel, H.
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p. 126 - 128
(2007/10/02)
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