Reactions In Aprotic Solvents Research Articles

Factors influencing kinetic isotope effects in some proton-transfer reactions in aprotic solvents

Kinetic studies have been carried out on the proton-transfer reactions of (i) 4-nitrobenzyl cyanide (4-NBC) with tetramethylguanidine (TMG) and (ii) 4-nitrophenylphenylcyanomethane (4-NPPCM) with 1,8-bis(dimethylamino)naphthalene (DMAN) in acetonitrile.The reaction (i) has a moderate enthalpy of activation (ΔH‡= 25 kJ mol–1) and a negative entropy of activation (ΔS‡=–98 J mol–1 K–1). The deuterium kinetic isotope effect is large.The reaction (ii) of the more hindered molecule 4-NPPCM and DMAN has similar activation parameters (ΔH‡= 26 kJ mol–1, ΔS‡=-140 J mol–1 K–1), but the kinetic isotope effect is considerably larger; also ΔHD‡-ΔHH‡ is large (13 kJ mol–1) and AH/AD is small, indicating a considerable tunnelling effect. Evidence that the large isotope effects are not artefacts of hydrogen exchange is presented. The tunnelling factor is estimated.

Application of the pressure-jump technique to the measurement of rates of fast reactions in non-aqueous solvents

Modifications to a pressure-jump autoclave are described which permit the measurement of rapid rates of reaction in aprotic solvents. In such solvents, a chemical system at equilibrium will generally be perturbed primarily by the temprature decrease which accompanies the adiabatic expansion process. The factors which determine the amplitude of the resulting relaxation transient are discussed, and kinetic data are reported for the fast proton-transfer reaction between the phenolic indicator acid bromophenol blue and the weak base pyridine in chlorobenzene and 1,2-dichlorobenzene. Results obtained by means of the pressure-jump method are in excellent agreement with those obtained using other fast reaction techniques.

An A.C. technique for determining the rates of rapid electrode reactions of aromatic compounds in aprotic media

An a.c. technique for measuring the rate constants for rapid electrode reactions in aprotic solvents using commercially available instrumentation with applied a.c. frequencies of 425 to 4250 Hz is described. A.c. Phase sensitive detection using a lock-in amplifier and a hanging mercury drop electrode was employed. Electrode kinetic parameters are given for phthalonitrile, terephthalonitrile, t-stilbene, nitrobenzene, m-dinitrobenzene, anthracene and perylene in N,N-dimethylformamide. Experimental details and the comparisons with previously reported results are discussed. The technical simplicity and good precision of this method makes it suitable for studying rapid electrode reactions in nonaqueous systems.

Regiospecific Michael reactions in aprotic solvents with .alpha.-silylated electrophilic olefins. Application to annelation reactions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRegiospecific Michael reactions in aprotic solvents with .alpha.-silylated electrophilic olefins. Application to annelation reactionsGilbert Stork and Janak SinghCite this: J. Am. Chem. Soc. 1974, 96, 19, 6181–6182Publication Date (Print):September 1, 1974Publication History Published online1 May 2002Published inissue 1 September 1974https://doi.org/10.1021/ja00826a038RIGHTS & PERMISSIONSArticle Views557Altmetric-Citations82LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (253 KB) Get e-Alerts Get e-Alerts

Proton phototransfer reactions in aprotic solvents

Proton phototransfer reactions in aprotic solvents

Reactions of bromonitroalkenes with tervalent phosphorus. Part I. Reaction in aprotic solvents

The reaction of a variety of 2-substituted 1-bromo-1-nitroethylenes with triphenylphosphine in benzene or ethyl acetate gave good yields of cyanomethyl(triphenyl)phosphonium salts, which on treatment with base afforded the corresponding ylides. An analogous cyanomethylphosphonate was obtained from a reaction with triethyl phosphite. Three alternative sites of initial attack by phosphine are considered in an attempt to explain the deoxygenation reaction; efforts to gain evidence for one of these (initial attack at halogen) were only partially successful.

Spectroscopic, thermodynamic, and kinetic evidence for a hydrogen-bonded intermediate in fast proton-transfer reactions in aprotic solvents

The system Bromophenol Blue + 2,4,6-trimethylpyridine in chlorobenzene shows appreciable quantities of both hydrogen-bonded and ion-pair complex species in protomeric equilibrium; the proton-transfer within the hydrogen bond proceeds at a rate of about 105 s–1, which is much slower than has been generally supposed.

The SN mechanism in aromatic compounds. XXXVII. Reactivity of amines

A semi-empirical theoretical procedure utilizing bond-dissociation, solvation, and ionization energies as the main terms is used to calculate reactivity of amines, which constitute the main class of neutral nucleophiles, with some typical neutral aromatic substrates in protic solvents; and their reverse, i.e. reactivity of anionic nucleophiles with cationic (ammonio) substrates. The procedure has previously been used successfully to calculate reactivity of anionic nucleophiles with neutral substrates. In each class the calculations also lead to estimates of other important parameters such as leaving group mobility. The procedure is applicable in principle to reactions of nucleophiles with other organic and with inorganic substrates and to reactions in aprotic solvents. ��� In this paper, the procedure is applied to some representative reactions of amines with neutral aromatic substrates in protic solvents and predicts, in accordance with experimental data where available, (i) reactivity in the order: NH3 < MeNH2 < Me2NH > Me3N; PhNH2 > PhNHMe > PhNMe2; MeNR2 > PhNR2 (R = H or Me); (ii) leaving group mobility in the order: F > Cl (and other heavy halogens) in the reactions of aliphatic amines and aniline; F > Cl in the reactions of N-methylaniline; and F < Cl in the reactions of N,N-dimethylaniline; (iii) small values of ΔE? ( ≈ ΔH? in solution reactions). Small values of log B (very negative values of ΔS?) are predictable on general theoretical grounds, and these are modified by steric factors. ��� Similar amine reactivity patterns are common with non-aromatic substrates, and the explanations given by the procedure are of general application, apart from differences in the steric factors.