Reactions of thiolate anions with 2-substituted-2-nitropropanes

Thiolates undergo substitution reactions with 2-substituted-2-nitropropanes by an S_RN1 mechanism or are oxidised to disulphides by an ionic mechanism.     

The reaction of carbanions with 2-substituted-2-nitropropanes : Substitution and dimerization occurring by radical chain processes involving electron transfer

The reaction of mono-enolate anions with O₂NCMe₂X where X = Cl, NO₂, p-MePhSO₂ yield coupling (RCOCH(R′)(CMe₂NO₂) and enolate dimerization products (RCOCH(R′)CH(R′)COR) by free radical chain mechanisms involving bimolecular substitution or electron transfer reactions between the enolate anion and the intermediate nitro alkane radical anion (XCMe₂NO₂^?).     

Quantum-chemical study on reactions of isocyanates with linear methanol associates: VII. Effect of nonspecific solvation on the reaction of methyl isocyanate with linear methanol associates

The effect of nonspecific solvation on the reactivity of methyl isocyanate toward linear methanol associates and thermodynamic parameters of this reaction was studied at the B3LYP/6-311++G(df,p) level of theory in terms of the polarizable continuum model (PCM). Transformations in the liquid phase are more exothermic than in the gas phase. Change of the solvent nature leads to variation of the geometric parameters and intrinsic free energies of the reactants and transition states. Increase in solvent polarity is accompanied by increase in the degree of asymmetry and polarity of transition states. As the dielectric permittivity rises, the polar constituent of the Gibbs energy of solvation decreases, while its nonpolar constituent increases. Owing to the opposite variations of these constituents of the Gibbs energy of activation, the reaction is weakly sensitive to solvent polarity.     

Chemoselective nucleophilic fluorination induced by selective solvation of the SN2 transition state

Reaction of the fluoride ion with secondary alkyl halides leads to 90% of elimination reaction and only 10% of nucleophilic substitution in dipolar aprotic solvents. Adding water to the organic phase, the SN2 yield increases in the cost of decreased reactivity. Using ab initio calculations, we have shown that it is possible to increase the reaction rate and the selectivity toward the SN2 process through supramolecular organocatalysis. The catalytic concept is based on selective solvation of the transition state through two hydrogen bonds provided by the 1,4-benzenedimethanol. The two hydrogen bonds between the catalyst and the SN2 transition state favor this pathway while just one strong hydrogen bond between the catalyst and the fluoride ion leads to a lower stabilization of the nucleophile, resulting in a higher reaction rate. Our calculations predict that the substitution product increases to 40% yield because of the selective catalysis provided by the 1,4-benzenedimethanol.     

氯化钙甲醇溶液中离子溶剂化作用的理论研究

利用红外光谱研究不同温度下CaCl2/甲醇溶液体系的溶剂化作用,结果表明在溶液中CaCl2以离子形式与甲醇发生溶剂化作用,且溶剂化数随温度升高而降低.通过密度泛函理论（DFT）在B3LYP/6-31G＊＊水平下对CaCl2/甲醇溶液中可能存在的配位构型进行结构优化及热力学性质的计算,说明了在CaCl2/甲醇溶液中各种配位构型存在的可能性,得出温度升高热力学数据的变化规律,解释了溶剂化数随温度升高而降低的趋势.进一步对各种可能配位构型的红外吸收频率进行计算并与实验结果进行比较,推断在CaCl2/甲醇溶液中主要存在的配位构型为[CaCl（CH3OH）n]＋和[Cl（CH3OH）n]-.     

Aromatic nucleophilic substitution reactions of 2-chloro-quinoxaline with anilines in ethanol

The reactions of 2-chloroquinoxaline with anilines in ethanol are found to follow second order kinetics, first order in each reactant. The activation parameters determined, from the rate data at five different temperatures are found to be typical of bimolecular aromatic nucleophilic substitutions (SN2Ar). The rate data are also correlated in terms of Hammett as well as Bronsted relationships.     

Steric Effects in Nucleophilic Aromatic Substitution reactions with aromatic amines 12th communication on nucleophilic aromatic substitution reactions

The kinetics of the S_NAr reactions of aniline and N-methylaniline with a variety of substituted nitrochlorobenzenes in acetonitrile demonstrate that the formation of the intermediate σ-complex is rate determining. The ratio of the rate constants of the aniline and the N-methylaniline reactions (k_A/k_M) increases with increasing size of the 6-substituent; with picryl chloride k_A/k_M reaches a value of over 20 000. The reaction of aniline with 4-X-2,6-dinitrochlorobenzenes is subject to considerably larger para-substituent effects than the corresponding reactions with N-methylaniline. These results are interpreted in terms of two effects: (i) A primary steric effect, which renders the approach of N-methylaniline to the substrate difficult. (ii) A shift towards earlier, more reactant-like transition state structures caused by the primary steric effect. In early transition states the activating power of the electron-withdrawing substituents in the substrate is expected to be relatively small. An early transition state for the slow N-methylaniline reaction and a late transition state for the fast aniline reaction is in apparent contradiction to what would be expected on the basis of the Hammond postulate.     

β-Aziridinylacroleins in reactions with nucleophilic reagents

The reactivities of -aziridinylcinnamaldehyde and -(2-methylaziridinyl)acrylaldehyde with respect to amines, hydrazines, and semicarbazide were studied, -Aminoacroleins were obtained by reaction of secondary amines with aziridinylacroleins. The reaction of aziridinylcinnamaldehyde with primary amines gives the corresponding imines. It was established that in its reaction with hydrazines and semicarbazide aziridinylacrolein is more inclined to undergo heterocyclization reactions (the formation of pyrazoles and pyrazolines) than aziridinylcinnamaldehyde.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 483–488, April, 1978.     

Some nucleophilic substitution reactions of 2-chloro-3-cyanopyridines

The chlorine atom in 2-chloro-3-cyanopyridines is readily replaced by primary and secondary aliphatic amines and heterocyclic amines to give 2-aminopyridines. 2-Chloro-3-cyanopyridines react with hydrazine hydrate and sodium azide to give hydrazinopyridines, pyridopyrazoles, azidopyridines, and pyridotetrazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1085–1088, August, 1976.     

Gas-phase elimination reactions of 4-substituted-2-alkoxythiazoline-5-ones

Gas-phase eliminations of 4-substituted-2-alkoxythiazoline-5-ones have been studied. These compounds eliminate via a six-membered transition state to produce 4-substituted-thiazolidine-2,5-diones. These eliminations are unimolecular first-order reactions. Utilization of this thermolysis reaction in the synthesis of new 4-substituted-thiazolidine-2,5-diones is considered. Additional mechanistic information was obtained by comparing the kinetic data for thermal elimination reactions of these compounds with that of 1-ethoxythiazole. © 1996 John Wiley & Sons, Inc.     

Negative solvation of diamagnetic ions in methanol

Analysis of intramolecular contributions calculated from selective T₁ measurements for hydroxyl and methyl protons of methanol solutions of diamagnetic salts provides evidence of a negative solvation effect for I^?, ClO₄^? and CNS^? ions. At low concentrations the microdynamic behaviour of the hydroxyl group is strongly affected whereas that of the methyl group appears to be unchanged.     

Proton solvation in methanol solutions of HCl

The MFTIR IR spectra of solutions of HCl in methanol were obtained in the 900–4000 cm^–1 frequency range. It was found that each proton binds two molecules of methanol. The spectra exhibit intense, continuous absorption (CA) with an intensity coefficient at 2000 cm^–1 of 174±10 liter/(mole·cm), which is in agreement with the corresponding coefficient for H₅O ₂ ⁺ . The optical densities of CA are linear functions of the concentration of HCl at 900–1600 cm^–1; there is no linearity at higher frequencies for C_HCl>4 M, and there are less than two molecules of MeOH for each (MeOH)₂H⁺ ion. The results obtained are in agreement with the model in which CA arises in solutions of strong acids because of the interaction of proton vibrations in a strong symmetric H bond with the vibrations of other groups of the proton disolvate.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2261–2268, October, 1992.     

Synthesis and nucleophilic displacement reactions of fluoropyrazine and 2-fluoroquinoxaline

An improved method for the preparation of fluoropyrazine (I) by halogen exchange and a synthesis of 2-fluoroquinoxaline (II) by a Balz-Schiemann reaction are presented. Compound I hydrolyzes slowly in 0.01N sodium hydroxide, rapidly in 1.07N sodium hydroxide at 26.00°. Compound II hydrolyzes 240 times faster than I in 0.01N sodium hydroxide at 26.00°. Hydrolysis of I in 6N hydrochloric acid at room temperature is slow. Compound I underwent nucleophilic reactions with formation of hydroxy, amino, methylamino, piperidino, benzylamino and anilinopyrazines. Pyrazinesulfonic acid was obtained from I and sodium sulfite and tetrazolo[1, 5-a]pyrazine (IV), a novel ring system, from I and sodium azide.     

Synthesis of 2-hydroxymethylene- and 2-dimethylaminomethylene-3-oxoquinuclidines and their reactions with nucleophilic reagents

The reaction of 3-oxoquinuclidine with ethyl formate in the presence of sodium and with dimethylformamide diethylacetal was used to synthesize 2-hydroxymethylene- and 2-dimethylaminomethylene-3-oxoquinuclidines, which upon reaction with amines from N-substituted 2-aminomethylene-3-oxoquinuclidines and upon reaction with hydrazine hydrate give pyrazolo [3,4-b]quinuclidines. The reaction of 2-aryl- and 2-heteroarylmethylene-3-oxoquinuclidines with hydrazine hydrate and thiourea, which led to the synthesis of pyrazolo[3,4-b]- and pyrimido[5,4-b]quinuclidines with aryl or heteroaryl substituents in the resulting ring, was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1232–1237, September, 1982.     

Reactivity of some 3-substituted-6,8-dimethylchromones toward some nucleophilic reagents

The reactivity of 3-substituted-6,8-dimethylchromone derivatives 1 - 5 was investigated toward selected nucleophilic reagents namely; 3-amino-1,2,4-triazole, 2-aminobenzimidazole, 7-chloro-4-hydrazinoquinoline, and 5,6-diphenyl-3-hydrazino-1,2,4-triazine. These nucleophiles were allowed to react with 6,8-dimethylchromone-3-carboxaldehyde ( 1 ) through condensation with the aldehyde group with opening of γ-pyrone ring giving compounds 6 , 7 , 10, and 11 . Reactions with 6,8-dimethylchromone-3-carbonitrile ( 2 ), and 6,8-dimethylchromone-3-carboxylic acid ( 3 ) occur via attack at position 2 in both compounds followed by cycloaddition onto the nitrile function (in case of carbonitrile 2 ) or decarboxylation and cyclocondensation with the carbonyl group (in case of carboxylic acid 3 ). The current nucleophilic reagents reacted with simple condensation products 4 and 5 , in boiling dioxane, through nucleophilic addition at the exocyclic vinyl bond followed by addition at the CN group giving 6,8-dimethylchromone linked various heterocyclic systems 20 - 27 .