Kinetic evidence for the occurrence of kinetically detectable intermediates in the cleavage of N‐ethoxycarbonylphthalimide under N‐methylhydroxylamine buffers

The kinetics of the aqueous cleavage of N‐ethoxycarbonylphthalimide (NCPH) in CH₃NHOH buffers of different pH reveals that the cleavage follows the general irreversible consecutive reaction path NCPH ENMBC A B , where ENMBC, A , and B represent ethyl N‐[o‐(N‐methyl‐N‐hydroxycarbamoyl)benzoyl]carbamate, N‐hydroxyl group cyclized product of ENMBC, and o ‐(N‐methyl‐N‐hydroxycarbamoyl)benzoic acid, respectively. The rate constant k_{1 obs} at a constant pH, obeys the relationship k_{1 obs} = k_w + k_n^app [Am]_T + k_b[Am]_T², where [Am]_T is the total concentration of CH₃NHOH buffer and k_w is first‐order rate constant for pH‐independent hydrolysis of NCPH. Buffer‐dependent rate constant k_b shows the presence of both general base and general acid catalysis. Both the rate constants k_{2 obs} and k_{3 obs} are independent of [Am]_T (within the [Am]_T range of present study) at a constant pH and increase linearly with the increase in a_OH with definite intercepts. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 95–103, 2002     

Concurrent two one‐electron transfer in the oxidation of chromium(III) complexes with trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetate and diethylenetriaminepentaacetate ligands by periodate ion

The kinetics of oxidation of [Cr^IIIcdta(H₂O)]^? and [Cr^IIIdtpa(H₂O)]^2? (where cdta = trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetate and dtpa = diethylenetriaminepentaacetate) by periodate ion has been studied in aqueous solutions. The oxidation of these complexes was carried out in the pH range 5.52–7.44 for the [Cr^IIIcdta(H₂O)]^? complex and the pH range 5.56–8.56 for the [Cr^IIIdtpa(H₂O)]^2? complex. The reaction exhibited an uncommon second‐order dependence on [Cr^IIIL(H₂O)]ⁿ (L = cdta or dtpa and n=?1 or ?2, respectively) and a first‐order dependence on [IO^?₄]. At fixed reaction conditions, the reaction rate is described by Eq. (i). The third‐order rate constant, k₃, varied with [H⁺] according to Eq. (ii). (i) (ii) A mechanism in which simultaneous one‐electron transfer from two [Cr^IIIL(OH)]^n?1 ions to I(VII) is proposed. The two [Cr^IIIL(OH)]^n?1 ions are bridged to I(VII) via the hydroxo group. Periodate ion is known to undergo rapid substitution or expansion of its coordination number from four to six. The activation parameters ΔH* and ΔS* were calculated using the Eyring equation. The relatively high negative values of ΔS* are consistent with an associative process preceding electron transfer. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 729–735, 2012     

Kinetic studies and mechanism on the permanganic oxidation of L‐Glutamine in strong acid medium in the presence and absence of Silver (I)

The kinetic study and mechanism of the permanganic oxidation of L‐glutamine in sulfuric acid has been carried out both in the absence and presence of silver (I) using a spectrophotometric technique. Activation parameters have been evaluated using the Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. The overall rate expression for the oxidation may be written as In the presence of silver (I) the rate law is The reaction appears to involve an acid catalyzed and data showed role of water molecules in the rate‐determining step is proton transfer which satisfies Bunnett's theory. A mechanism satisfying the various kinetic parameters has been proposed. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 95–102, 1999     

Side‐chain polypseudorotaxanes by threading cucurbit[7]uril onto poly‐N‐n‐butyl‐N′‐(4‐vinylbenzyl)‐4,4′‐bipyridinium bromide chloride: Synthesis,characterization, and properties

A novel side‐chain polypseudorotaxanes P4VBVBu/CB[7] was synthesized from poly‐N‐n‐butyl‐N′‐(4‐vinylbenzyl)‐4,4′‐bipyridinium bromide chloride (P4VBVBu) and cucurbit [7]uril (CB[7]) in water by simple stirring at room temperature. CB[7] beads are localized on viologen units in side chains of polypseudorotaxanes as shown by ¹H NMR, IR, XRD, and UV–vis studies, and it is considered that the hydrophobic and charge‐dipole interactions are the driving forces. TGA data show that thermal stability of the polypseudorotaxanes increases with the adding of CB[7] threaded. DLS data show that P4VBVBu and CB[7] could form polypseudorotaxanes, and the average hydrodynamic radius of the polypseudorotaxanes increases with increasing the concentration of CB[7]. The typical cyclic voltammograms indicate that the oxidation reduction characteristic of P4VBVBu is remarkably affected by the addition of CB[7] because of the formation of polypseudorotaxanes and the shielding effects of CB[7] threaded on the viologen units of polypseudorotaxanes. With the increase of the concentration of KBr or K₂SO₄, the formation of the polypseudorotaxanes was inhibited due to the shielding effects of both Br^? or SO to viologen ion and K⁺ to CB[7] by UV–vis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2135–2142, 2010     

Electrochemiluminescent Determination of Chlorphenamine Maleate Based on Ru(bpy)$\rm{ {_{3}^{2+}}}$ Immobilized in a Nano‐Titania/Nafion Membrane

The immobilization of tris(2,2'‐bipyridyl)ruthenium(II) [Ru(bpy) ] in a TiO₂/Nafion nanocomposites membrane modified glassy carbon electrode (GCE) was achieved via both an ion‐exchange process and hydrophobic interactions .The surface‐confined Ru(bpy) shows good electrochemical and photochemical activities. The Ru(bpy) underwent reversible surface process and reacted with chlorphenamine maleate (CPM) to produce electrochemiluminescence. The modified electrode was used for the ECL determination of CPM. It showed good linearity in the concentration range from 2×10^?8 g/mL to 1×10^?6 g/mL (R=0.9995) with a detection 6×10^?9 g/mL (S/N=3). The relative standard derivation (n=11) was 2%. This method is developed for the determination of CPM with simplicity and high sensitivity.     

The analytical resolution of parallel first‐ and second‐order reaction mechanisms

Given the species A₁ and A₂, the competition among the three different elementary processes (1) (2) (3) is frequently found in thermal and photochemical reaction systems. In the present paper, an analytical resolution of the system (1)–(3), performed under plausible contour conditions, namely, finite initial molar concentrations for both reactants, [A₂]₀ and [A₁]₀, and nonzero reaction rate coefficients k₁, k₂, and k₃, leads to the equation [A₁] = ((δ[A₂]^γ ? [A₂])/β) ? α, where α = k₁/2k₃, γ = β + 1 = 2k₃/k₂, and δ = ([A₂]₀ + β[A₁]₀ + β α))/[A₂]₀^γ. The comparison with a numerical integration employing the fourth‐order Runge–Kutta algorithm for the well‐known case of the oxidation of organic compounds by ferrate ion is performed. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 562–566, 2010     

Temperature and shear dependencies of rheology of poly(acrylonitrile‐co‐itaconic acid) dope in DMF

Poly(acrylonitrile‐co‐itaconic acid) (poly(AN‐co‐IA)) precursor required for carbon fiber production is made into a dope and spun into fibers using a suitable spinning technique. The viscosity of the resin dope is decided by the polymer concentration, polymer molecular weight, temperature, and shear force. The shear rheology of concentrated poly(AN‐co‐IA) polymer solutions in N,N‐dimethylformamide (DMF), in the range of 1 × 10⁵–1 × 10⁶ g mol^?1, has been investigated in the shear rate (γ′) range of 1 × 10¹–5 × 10⁴ min^?1. The zero shear viscosity (η₀) has been evaluated at different temperatures. The temperature dependence of zero shear viscosity conformed to the Arrhenius–Frenkel–Eyring model. The free energy of activation of viscous flow (ΔG_V) values were in the range 5–32 kJ mol^?1 and this value increased with increase in polymer concentration and molecular weight. A master equation for the ΔG_V value of the polymer solution of any and concentration (c) is suggested. The power law fitted well for the shear dependency of viscosity of these polymer solutions. The pseudoplasticity index (n) diminished with increase in polymer concentration and molecular weight. An empirical relation between viscosity (η) and was found to exist at constant shear rate, concentration and temperature. For each , the equation relating n, c, and T was established. Copyright © 2008 John Wiley & Sons, Ltd.     

The method of asymptotic approximations as applied to analyzing the mechanism of inhibited liquid-phase oxidation

A new method for analyzing the problems of chemical kinetics is elaborated involving the technique of mathematical modeling. Namely, the matching method of the asymptotic expansion is applied to analyzing the inhibition mechanism of oxidation. The proposed approach is an extension of the well-known method of quasi-stationary concentrations and may be applied to study a series of problems in the field of chemical kinetics. Three different time scales were established for the mechanism of inhibited oxidation under restrictions k₇[InH]₀/(2k₆W_i)^1/2 ? 1 and k₈ ? 2k₆ ? k₇. At the first time scale (that is very fast and is measured in second fractions) the concentration of radicals In only changes while [RO₂] ? [RO₂]₀, [In H] ? [In H]₀ are constants. At the second time scale (s), [RO₂] changes while [In] ? [In]_st, [In H] ? [In H]₀ are constants. At the third time scale (min), [In H] changes. An asymptotic analysis of the differential equations allows us to find out both the time duration of each step and the variation of the component which changes at this step. After that the rate constants k₈, 2k₆, k₇ are determined from comparison with the experimental measurements of [In], [RO₂], and [In H]. Due to the simplicity and efficiency of the asymptotic method, one may be applied to treating the complex multicenter radical chain processes such as conjugated oxidation, radical copolymerization, sulfoxidation, etc. © 1993 John Wiley & Sons, Inc.     

Effects of CH3OH‐H2O and CH3OH solvents on rate of reaction of phthalimide with piperidine

Pseudo‐first‐order rate constants (k_obs) for the cleavage of phthalimide in the presence of piperidine (Pip) vary linearly with the total concentration of Pip ([Pip]_T) at a constant content of methanol in mixed aqueous solvents containing 2% v/v acetonitrile. Such linear variation of k_obs against [Pip]_T exists within the methanol content range 10%–∼80% v/v. The change in k_obs with the change in [Pip]_T at 98% v/v CH₃OH in mixed methanol‐acetonitrile solvent shows the relationship: k_obs = k[Pip]_T + k[Pip], where respective k and k represent apparent second‐order and third‐order rate constants for nucleophilic and general base‐catalyzed piperidinolysis of phthalimide. The values of k_obs, obtained within [Pip]_T range 0.02–0.40 M at 0.03 M NaOH and 20 as well as 50% v/v CH₃OH reveal the relationship: k_obs = k₀/(1 + {k_n[Pip]/k_OX[⁻OX]_T}), where k₀ is the pseudo‐first‐order rate constant for hydrolysis of phthalimide, k_n and k_OX represent nucleophilic second‐order rate constants for the reaction of Pip with phthalimide and for the XO⁻‐catalyzed cyclization of N‐piperidinylphthalamide to phthalimide, respectively, and [⁻OX]_T = [NaOH] + [⁻OX_re], where [⁻OX_re] = [⁻OH_re] + [CH₃O_re⁻]. The reversible reactions of Pip with H₂O and CH₃OH produce ⁻OH_re and CH₃O_re⁻ ions. The effects of mixed methanol‐water solvents on the rates of piperidinolysis of PTH reveal a nonlinear decrease in k with the increase in the content of methanol. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 29–40, 2001     

On the calculation of arbitrary multielectron molecular integrals over Slater‐type orbitals using recurrence relations for overlap integrals. III. Auxiliary functions \documentclass{article}\pagestyle{empty}\begin{document}$Q_{nn'}^{q}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$G_{-nn'}^{q}$\end{document}

The auxiliary functions $Q_{nn'}^{q}(p,pt)$ and $G_{-nn'}^{q}(p_{a},p,pt)$ which are used in our previous paper [Guseinov, I. I.; Mamedov, B. A. Int J Quantum Chem 2001, 81, 117] for the computation of multicenter electron‐repulsion integrals over Slater‐type orbitals (STOs) are discussed in detail, and the method is given for their numerical computation. The present method is suitable for all values of the parameters p_a, p, and pt. Three‐ and four‐center electron‐repulsion integrals are calculated for extremely large quantum numbers using relations for auxiliary functions obtained in this paper. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Electrochemical Ammonia Gas Sensing in Nonaqueous Systems: A Comparison of Propylene Carbonate with Room Temperature Ionic Liquids

First, the direct and indirect electrochemical oxidation of ammonia has been studied by cyclic voltammetry at glassy carbon electrodes in propylene carbonate. In the case of the indirect oxidation of ammonia, its analytical utility of indirect for ammonia sensing was examined in the range from 10 and 100 ppm by measuring the peak current of new wave resulting from reaction between ammonia and hydroquinone, as function of ammonia concentration, giving a sensitivity 1.29×10^?7 A ppm^?1 (r²=0.999) and limit‐of‐detection 5 ppm ammonia. Further, the direct oxidation of ammonia has been investigated in several room temperature ionic liquids (RTILs), namely 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([C₄mim] [BF₄]), 1‐butyl‐3‐methylimidazolium trifluoromethylsulfonate ([C₄mim] [OTf]), 1‐Ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₂mim] [NTf₂]), 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₄mim] [NTf₂]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄mim] [PF₆]) on a 10 μm diameter Pt microdisk electrode. In four of the RTILs studied, the cyclic voltammetric analysis suggests that ammonia is initially oxidized to nitrogen, N₂, and protons, which are transferred to an ammonia molecule, forming NH via the protonation of the anion(s) (A^?). However, in [C₄mim] [PF₆], the protonated anion was formed first, followed by NH . In all five RTILs, both HA and NH are reduced at the electrode surface, forming hydrogen gas, which is then oxidized. The analytical ability of this work has also been explored further, giving a limit‐of‐detection close to 50 ppm in [C₂mim] [NTf₂], [C₄mim] [OTf], [C₄mim] [BF₄], with a sensitivity of ca. 6×10^?7 A ppm^?1 (r²=0.999) for all three ionic liquids, showing that the limit of detection was ca. ten times larger than that in propylene carbonate since ammonia in propylene carbonate might be more soluble in comparison with RTILs when considering the higher viscosity of RTILs.     

Light‐Switchable Polymer from Cationic to Zwitterionic Form: Synthesis,Characterization, and Interactions with DNA and Bacterial Cells

A novel cationic polymer poly(N,N‐dimethyl‐N‐[3‐(methacroylamino) propyl]‐N‐[2‐[(2‐nitrophenyl)methoxy]‐2‐oxo‐ethyl]ammonium chloride) is synthesized by free‐radical polymerization of N‐[3‐(dimethylamino)propyl] methacrylamide and subsequent quaternization with o‐nitrobenzyl 2‐chloroacetate. The photolabile o‐nitrobenzyl carboxymethyl pendant moiety is transformed to the zwitterionic carboxybetaine form upon the irradiation at 365 nm. This feature is used to condense and, upon the light irradiation, to release double‐strand DNA tested by gel electrophoresis and surface plasmon resonance experiments as well as to switch the antibacterial activity to non‐toxic character demonstrated for Escherichia coli bacterial cells in solution and at the surface using the self‐assembled monolayers.

     

Synthesis of 2‐formyl‐1‐aza‐dibenzo[e,h]azulenes

Synthesis of a novel heterocyclic class of compounds, 1‐aza‐dibenzo[e,h]azulenes [1] ( 6a‐c and 7a‐c ), derived from dibenzo[b,f]oxepin, its 8‐chloro analogue and dibenzo[b,f]thiepin, respectively, is described. Aldol condensation of the starting ketones 4a‐c with (dimethyl‐hydrazono)‐acetaldehyde affords hydrazonoethylidene derivatives 5a‐c , which on reduction with sodium dithionite and subsequent cyclization provide the target tetracyclic 1‐aza‐dibenzo[e,h]azulenes 6a‐c . Regiospecific formylation of 6a‐c with Vilsmeier reagent leads to 2‐formyl derivatives 7a‐c . A series of derivatives 6a‐c and 7a‐c was tested for antiinflammatory activity as potential inhibitors of tumor necrosis factor alpha (TNF‐α) production in vitro.     

Calixarene‐Based Surfactants: Conformational‐Dependent Solvation Shells for the Alkyl Chains

Thermodynamic parameters obtained from studying the micellization of amphiphilic p‐sulfonatocalix[n]arenes were correlated with the alkyl chain length and with the number of monomeric units (n) in the calix[n]arene structure. The micellization Gibbs free energy (Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ ) becomes more negative upon increasing the alkyl chain length of the p‐sulfonatocalix[4]arene. This is in agreement with the trend generally observed for other surfactants. However, the Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ value for transferring one CH₂ group from the bulk aqueous medium to the micelle [Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ (CH₂)] is lower than the value generally observed for single‐chain surfactants, suggesting the existence of intramolecular interactions between the alkyl chains of the free unimers. On the other hand, the critical micelle concentration (cmc; per alkyl chain unit) increased with the increasing number of monomeric units. These results are explained on the basis of the conformation adopted by the calixarene in the bulk solution. The calix[4]arene derivatives are preorganized into the cone conformation, which is favorable for the formation of globular aggregates. The calix[6]arene and calix[8]arene derivatives do not adopt cone conformations. Changing these conformations to the more favorable cone conformer in the aggregates implies an energetic cost that contributes to making Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ less efficient. In the case of the calix[6]arene derivative this energetic cost is enthalpic, whereas in the case of the octamer it is both enthalpic and entropic. Both the Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ (CH₂) value and the change in heat capacity (ΔC${{\rm p}{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ ) seem to indicate that for the cone calix[4]arene derivatives all alkyl chains are solvated by the same hydration shell, whereas in the case of the highly flexible calix[8]arene derivative each alkyl chain is individually hydrated.     

Synthesis and antibacterial studies of 6‐aryl‐2,2a‐dihydro‐naphtho‐[2′,1′‐5,6]pyrano[4,3‐e][1,2,4]triazolo[3,4‐b][1,3,4]thiadiazine and its derivatives

Chemoselective synthesis of novel hetero cyclopenta[b]chrysene derivatives, namely, 6‐Aryl‐2,2a‐dihydro‐naphtho[2′,1′‐5,6]pyrao[4,3‐e][1,2,4]triazolo[3,4‐b][1,3,4]thiadiazine ( 4a‐j ) under neutral condition has been described. These molecules exhibited good to excellent anti‐bacterial activities.     

Generation of N‐Heterocycles via Tandem Reactions of N ′‐(2‐Alkynylbenzylidene)hydrazides

As a powerful synthon, N ′‐(2‐alkynylbenzylidene)hydrazides have been utilized efficiently for the construction of N‐heterocycles. Since N ′‐(2‐alkynylbenzylidene)hydrazides can easily undergo intramolecular 6‐endo cyclization promoted by silver triflate or electrophiles, the resulting isoquinolinium‐2‐yl amides can proceed through subsequent transformations including [3 + 2] cycloaddition, nucleophilic addition, and [3 + 3] cycloaddition. Several unexpected rearrangements via radical processes were observed in some cases, which afforded nitrogen‐containing heterocycles with molecular complexity. Reactive partners including internal alkynes, arynes, ketenimines, ketenes, allenoates, and activated alkenes reacted through [3 + 2] cycloaddition and subsequent aromatization, leading to diverse H‐pyrazolo[5,1‐a]isoquinolines with high efficiency. Nucleophilic addition to the in situ generated isoquinolinium‐2‐yl amide followed by aromatization also produced H‐pyrazolo[5,1‐a]isoquinoline derivatives when terminal alkynes, carbonyls, enamines, and activated methylene compounds were used as nucleophiles. Isoquinoline derivatives were obtained when indoles or phosphites were employed as nucleophiles in the reactions of N ′‐(2‐alkynylbenzylidene)hydrazides. A tandem 6‐endo cyclization and [3 + 3] cycloaddition of cyclopropane‐1,1‐dicarboxylates with N ′‐(2‐alkynylbenzylidene)hydrazides was observed as well. Small libraries of these compounds were constructed. Biological evaluation suggested that some compounds showed promising activities for inhibition of CDC25B, TC‐PTP, HCT‐116, and PTP1B.

     

Flash vacuum pyrolysis of 1‐azolyl‐1‐phenylhydrazono‐2‐propanones

Flash vacuum pyrolysis (FVP) of 1‐(2‐arylhydrazono)‐1‐(1H‐1,2,4‐triazol‐1‐yl)acetone 8a‐c at 650 °C and 2.67 Pa yielded 5‐substituted 1‐(1H‐indazol‐3‐yl)ethanone 14a‐c and 4,6‐disubstituted cinnoline 18a‐c . Similarly FVP of 1‐(1H‐benzo[d]imidazol‐1‐yl)‐1‐(2‐phenylhydrazono)acetone 9a‐c gave 8H‐benzo[4′,5′]imidazo[2′,1′:5,1]pyrrolo[2,3‐c]cinnoline derivatives 23a‐c . A plausible mechanism is suggested to account for their transformation based on the kinetics and products of reaction.     

Mechanism of the hydroxyiodination of 2-butenoic acid

Aqueous iodination of trans-2-butenoic acid proceeds via hydrolysis of I₂ to form HOI and I^?, then rapid addition of HOI across the double bond to form the iodohydrin product. In the presence of iodate to keep iodide concentration low, the reaction proceeds at a conveniently measurable rate. The rate for the addition reaction is ?d[C₄H₆O₂]/dt = 5900 [H⁺][C₄H₆O₂][HOI]M/s at 25.0°C when [IO] = 0.025M and ionic strength = 0.3. The overall rate law in the presence of iodate is where [H⁺] and [IO] are total concentrations used to prepare the solution.     

Synthesis Of 1,8‐dioxa‐dibenzo[e,h]azulenese

A novel synthetic route to 2‐methyl‐1,8‐dioxa‐dibenzo[e,h]azulenes [1] via cyclisation of the corresponding 1,4‐dicarbonyl compound is described. 1,4‐Dicarbonyl compounds were synthesized by the alkylation reaction of the 11H‐dibenzo[b,f]oxepine‐10‐one while analogous alkylation of 11H‐dibenzo[b,f]thiepine‐10‐one resulted in formation of O‐alkylated products. Selective oxidation of 2‐methyl group afforded 1,8‐dioxa‐dibenzo[e,h]azulenes with formyl and hydroxymethyl functionality at C(2) position.     

Mechanistic Investigation of the Dipolar [2+2] Cycloaddition–Cycloreversion Reaction between 4‐(N,N‐Dimethylamino)phenylacetylene and Arylated 1,1‐Dicyanovinyl Derivatives To Form Intramolecular Charge‐Transfer Chromophores

The kinetics and mechanism of the formal [2+2] cycloaddition–cycloreversion reaction between 4‐(N,N‐dimethylamino)phenylacetylene ( 1 ) and para‐substituted benzylidenemalononitriles 2 b – 2 l to form 2‐donor‐substituted 1,1‐dicyanobuta‐1,3‐dienes 3 b – 3 l via the postulated dicyanocyclobutene intermediates 4 b – 4 l have been studied experimentally by the method of initial rates and computationally at the unrestricted B3LYP/6‐31G(d) level. The transformations were found to follow bimolecular, second‐order kinetics, with ${{\rm{\Delta }}H_{{\rm{exp}}}^{ {\ne} } }$ =13–18 kcal mol^?1, ${{\rm{\Delta }}S_{{\rm{exp}}}^{ {\ne} } }$ ≈?30 cal K^?1 mol^?1, and ${{\rm{\Delta }}G_{{\rm{exp}}}^{ {\ne} } }$ =22–27 kcal mol^?1. These experimental activation parameters for the rate‐determining cycloaddition step are close to the computational values. The rate constants show a good linear free energy relationship (ρ=2.0) with the electronic character of the para‐substituents on the benzylidene moiety in dimethylformamide (DMF), which is indicative of a dipolar mechanism. Analysis of the computed structures and their corresponding solvation energies in acetonitrile suggests that the rate‐determining attack of the nucleophilic, terminal alkyne carbon onto the dicyanovinyl electrophile generates a transient zwitterion intermediate with the negative charge developing as a stabilized malononitrile carbanion. The computational analysis predicted that the cycloreversion of the postulated dicyanocyclobutene intermediate would become rate‐determining for 1,1‐dicyanoethene ( 2 m ) as the electrophile. The dicyanocyclobutene 4 m could indeed be isolated as the key intermediate from the reaction between alkyne 1 and 2 m and characterized by X‐ray analysis. Facile first‐order cycloreversion occurred upon further heating, yielding as the sole product the 1,1‐dicyanobuta‐1,3‐diene 3 m .