The kinetics of the reactions among isoquinoline, dimethyl acetylenedicarboxylate, and 3‐methyl indole (as NH‐acid) was studied using UV spectrophotometry. The overall rate constant (kov) was evaluated from the slope of the plot of kobs versus reactant concentration. A large deal of useful information was obtained from the study of the effects of solvent, temperature, and reactants and concentration on the reaction rates. Based on experimental data and theoretical concepts, the reaction's first step (k1) was recognized as the rate‐determining step. Theoretical studies were performed to evaluate potential energy surfaces of all components participated in the reaction mechanism. Furthermore, the proposed mechanism was confirmed by the obtained results. The probable reaction path and product configuration were suggested based upon the theoretical results.

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Intermolecular proton transfer in barbituric acid (BA), both in the gas phase and in the presence of water molecule, was investigated using B3LYP method with aug-cc-pVDZ basis set. The overall process involves keto-enol and lactam-lactim tautomerism. The most stable form of barbituric acid turns into the intermediates with three step proton transfer at three different positions of the structure of this compound. Then, these intermediates become the final products passing from two competing processes. In order to determine the priority of each competitive process, energy changes of all possible tautomeric forms were investigated along the role of solvent molecules in multiple routes. Also, transposition in the proton-transfer process makes changes in the electron-transfer energy which was investigated both in the gas phase and in the presence of water molecules. Frequency calculations were performed to characterize ground and transition states and calculation of zero point energies. Natural bond orbital analysis and topological property of electron density were investigated using natural bond orbital (NBO) and atoms in molecules (AIM) analysis. From the results, all proton transfer processes in the gas phase and in the presence of the solvent molecule (water) is exothermic and non-spontaneous. In the gas phase and in the water assisted condition, the route 1b is kinetically more preferred. Despite the increase of the ring resonance of stronger hydrogen bonds in the product as compared to the reactant, the products are more unstable than the reactant. Therefore, the only factor that can make the product unstable is the severe decrease of LP (N) →σ* (C-O) electron-transfer energy.

In the recent work, kinetics studies were made of the reactions between triphenylphosphine 1, dialkyl acetylenedicarboxylates 2 in the presence of NH-acid, such as indazole 3. The kinetic parameters of all reactions determined by UV spectrophotometry. The second order fits were drawn and the values of the second order rate constant (k) were calculated using standard equations. All reactions repeated at different solvents and temperatures. Furthermore, useful information was obtained from studies of the effect of solvent, the structure of the reactants (dialkyl acetylenedicarboxylates) and also the concentration of reactants on the reaction rates. Theoretical studies were performed for evaluation of potential energy surfaces of all structures participated in the reaction mechanism. The first step of all reactions was recognized as a rate-determining step in the reaction mechanism, on the basis of experimental and theoretical data. Theoretical studies performed for evaluation of potential energy surfaces of all structures participated in the reaction mechanism. Quantum mechanical calculations were clarified that how the ylides exist, in solution, as a mixture of two geometrical Z-and E-isomers as a minor or major form.