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Ab initio molecular dynamics simulations in water solution are used to explore the mechanism of base-induced beta-elimination reactions in systems activated by the pyridyl ring, with halogen leaving groups. The results have shown that the reaction mechanism effectively evolves through the potential energy region of the carbanion, where the carbon-fluoride bond breaks only after the carbon-hydrogen bond.

The trans-bis[2-(2-chloroethyl)pyridine]palladium chloride was prepared and structurally characterized by X-ray spectroscopy and computational study. The reaction of the palladium complex with quinuclidine in CH(sub 3)CN, at 25 degree Celsius, leads to competing elimination and displacement reactions with formation of vinylpyridine and chloroethylpyridine in the ratio of 1.5:1.

A combined experimental and theoretical study is reported to characterize the mechanism of base-induced beta-elimination reactions in systems activated by the pyridyl ring with halogen leaving groups. The systems investigated represent bordering cases, where it is uncertain whether the reaction proceeds via a carbanion intermediate or via the concerted loss of a proton and the halide upon base attack.

A novel synthetic route to substituted 1(2H)-phenanthrenones was developed based on the ceric ammonium nitrate-promoted oxidative addition of 3-aryl-1-{(trimethylsilyl)oxy}-cyclohexanes to ethyl vinyl ether. The findings showed that the cyclization process had a high degree of stereoselectivity with the introduction of 3-Y-substituted aryl derivatives. The results also revealed that 6-substituted 3,4-dihydrophenenthren-1-ones were the critical regioisomers under all conditions considered.

The second-order rate constants for beta-elimination are determined for the title reactions in OH(super -)/H2O and in OH(super -)/(CH3CN/H2O) [30/70, 60/40 and 85/15 (v/v) mixtures].The methyl activating factors (k(sub OH(super -))(super NCH3)/k(sub OH(super -))(super N)) are slightly affected by the solvent composition and the high acceleration of the reaction by methylation of the pyridine ring amounts to 10(super 4)-10(super 6) according to an E1cb mechanism.

The experiment conducted to study the catalysis of the beta-elimination reaction of N-[2-(4-pyridyl)ethyl]quinuclidinium and N-[2-(2-pyridyl)ethyl]quinuclidinium by Zn2+ and Cd2+ in OH-/H2O (pH = 5.20-6.35,50degreeC, and mu = 1M KCl) is presented.

The study on N-[2-(4-pyridyl)ethyl]quinuclidinium and N-[2-(2-pyridyl)-ethyl]quinuclidinium at 50 degree Celsius, Mu=1 M KCL, in different buffer systems and different pH ranges is reported.

Research has been conducted on beta-elimination reactions. The mechanism of the base-induced beta-elimination reactions in pyridine ring activated systems with fluorine as a leaving group is described.

The behaviour of 1-(2-bromoethyl) 4-nitrobenzene (1), N,N,N-triethyl-2-(4-nitrophenyl)ethanaminium bromide (2) and N,N-diethyl-N-[2-(4-nitrophenyl)ethyl]octan-1-aminium bromide (3) in the OH--induced elimination reactions with formation of 1-nitro-4-vinylbenzene in mixtures of DMSO/H2O or CH3CN/H2O has been investigated. With all three substrates an increase in dipolar aprotic solvent content implies a limited increase of the second-order rate constant kOH up to ≅60%, and then an exponential increase is observed. The variation of activation parameters ΔH# and ΔS#, measured in DMSO/H2O mixtures, is parallel for 1 and 2. This similar behaviour of 1 and 2 with respect to variation in solvent composition is evidence that it is not possible to use this technique of solvent effect for the mechanistic diagnosis of elimination reactions. [ABSTRACT FROM AUTHOR]

β-Elimination reactions from 1 (in quinuclidine/quinuclidinium chloride, imidazole/imidazolium, and acetate/acetic acid buffers) and from 2 (in imidazole/imidazolium and acetate/acetic acid buffers) with formation of 4-vinylpyridine and 2-vinylpyridine, respectively, were studied. The results of a kinetic study of acid-base catalysis and H/D exchange are consistent with NH+, the protonated substrate, as the species that undergoes carbon deprotonation with an E1cb mechanism. The comparison with previously studied reactions in acetohydroxamate/acetohydroxamic acid buffer confirms this assignment. The high proton activating factor, PAF, value observed (PAF = 1.2 × 10 6 with isomer 1 in quinuclidine/quinuclidinium buffer) can be explained with the high stability by the resonance of the intermediate carbanion. [ABSTRACT FROM AUTHOR]

Second-order rate constants have been determined for the title reactions in OH-/H2O and in OH-/ (CH3CN/H2O) [30/70, 60/40, and 85/15 (v/v) mixtures]. A relatively small increase in reactivity is observed for the four substrates upon increasing the percentage of CH3CN in the solvent mixture. The methyl activating factors (kOH-NCH3/kOH-N) are also slightly affected by the solvent composition. On the other hand, the high acceleration of the reaction by methylation of the pyridine ring amounts to 104-106 according to an E1cb mechanism. [ABSTRACT FROM AUTHOR]