1,721,055 research outputs found
Synthetic approach to novel NMP/ALK inhibitors
No full textSynthetic approach to novel NMP/ALK inhibitor
Protonation Equilibrium of Esters in Aqueous Sulfuric Acid
No full textThe protonation equilibrium of methyl esters RCOOCH3 (R = Me, Et, i-Pr, t-Bu, Ph) has been investigated in aqueous sulfuric acid at 25 C with the NMR technique. Experimental points show systematic differences from the theoretical curves which prevent an accurate determination of the protonation parameters. By analogy with the observations made on ketones, it is suggested that the formation of a hydrogen-bonded complex between the ester molecule and the hydronium ion is responsible for this behaviour, and a procedure is presented which allows for the treatment of the two simultaneous equilibria (protonation and complexation), thus obtaining pure protonation parameters. The trend of m* and pK in the series if discussed in terms of the relative stabilization of the protonated ester by internal external charge dispersal, and compared to the analogous data for ketones
Heterodialkyl Trigonal Bipyramidal 5-ansa-Zirconocenes. Kinetics of the rearrangement reaction of [Zr{C5H3N(CH2C5H4)2-2,6}(n-C4H9)(CH3)]
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Different Approaching Directions of sigma and pi Nucleophiles to the Sulfur Atom of Thiiranium and Thiirenium Ions
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The Influence of Hydration on the Protonation Equilibria of Aliphatic Ketones in Aqueous Sulfuric Acid
No full textThe protonation equilibrium of methyl ketones RCOCH3 (R = Me, Et, i-Pr, t-Bu) and of di-t-butyl ketone have been investigated in aqueous sulfuric acid at 25 C by means of UV and NMR spectroscopies. Both techniques yield experimental points which display systematic differences from theoretical curves. The various possible sources of perturbation are discussed, and it is concluded that a specific interaction of ther ketone molecules with the hydronium ion is responsible for the observed deviations. A solution to this two-equilibrium system is presented, which yields m* and pK values of 0.35 and -3.06, respectively, for acetone (see eq. (5) in the text for the explanation of symbols). Similar values are found for the other methyl ketones, and very different values (0.85 and -7.24, respectively) for di-t-butyl ketone
An Authentic Case of In-plane Nucleophilic Vinylic Substitution: the Anionotropic Rearrangement of Di-tert-butylthiirenium Ions into Thietium Ions
No full textEnantiopure Thiosulphonium Salts in Asymmetric Synthesis. Face Selectivity in Electrophilic Additions to Unfunctionalized Olfins
No full textThiiranium and Thiirenium Ions. From Reaction Intermediates to Building Blocks in Organic Synthesis
No full textSN2 and AdN-E Mechanisms in Bimolecular Nucleophilic Substitutions at Vinyl Carbon. The Relevance of the LUMO Symmetry of the Electrophile
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