The thesis of this paper is that orbital symmetry allowedness does not guarantee concert. The activation energy (E_a) for concerted Diels–Alder and 1,3-dipolar cycloadditions must be substantially lower than that for a stepwise-diradical pathway because the diradical has two fewer bonding electrons than anything on the concerted reaction coordinate, including the transition state. Two bonding electrons provide tens of kcal/mol of stabilization. The difference between the experimental E_a and that for diradicals is called the energy of concert (E_con). If experiment represents concert, E_con must be large, and if it represents diradicals E_con will be very small. In this paper, 42 examples are adduced in which firm experimental data show that E_con = 0. These cycloadditions cannot be concerted. While concert remains possible for all cycioadditions not proven stepwise, there is none with compelling evidence for concert.

A detailed chemical kinetic model for oxidation of carbonyl sulfide (OCS) has been developed, based on a critical evaluation of data from the literature. The mechanism has been validated against experimental results from batch reactors, flow reactors, and shock tubes. The model predicts satisfactorily oxidation of OCS over a wide range of stoichiometric air–fuel ratios (0.5 ), temperatures (450–1700 K), and pressures (0.02–3.0 atm) under dry conditions. The governing reaction mechanisms are outlined based on calculations with the kinetic model. The oxidation rate of OCS is controlled by the competition between chain-branching and -propagating steps; modeling predictions are particularly sensitive to the branching fraction for the OCS + O reaction to form CO + SO or CO₂ + S.

Henry's law constants of six kinds of hydrochlorofluorocarbons (HCFCs) were determined at 313–353 K by means of a phase-ratio variation headspace method: and (K_H³⁵³ in M atm⁻¹, ΔH_sol in kJ mol⁻¹) = (0.0070 ± 0.0006, –23 ± 2), (0.0038 ± 0.0011, –22 ± 10), (0.0065 ± 0.0007, –21 ± 3), (0.0026 ± 0.0007, –23 ± 8), (0.0016 ± 0.0003, –30 ± 4), and (0.0022 ± 0.0003, –25 ± 4), respectively, for HCFC-141b (CH₃CCl₂F), HCFC-142b (CH₃CClF₂), HCFC-123 (CF₃CHCl₂), HCFC-124 (CF₃CHClF), HCFC-225ca (CF₃CF₂CHCl₂), and HCFC-225cb (CClF₂CF₂CHClF). Errors represent two standard deviations only for the fitting. The decay of headspace partial pressures of these HCFCs via hydrolysis was discerned only for CF₃CHCl₂ and CF₃CF₂CHCl₂ under the experimental conditions examined. Rate constants (k_OH– in M⁻¹ s⁻¹) for aqueous reactions of CF₃CF₂CHCl₂ and CF₃CHCl₂ with OH⁻ at 313–353 K were determined to be and , respectively, from monitoring changes in headspace partial pressure over prescribed concentrations of aqueous NaOH as a function of the headspace time duration and concentration of aqueous NaOH. The calculations performed included consideration of gas–water equilibrium and hydrolysis at both headspace and room temperatures. The calculation for CF₃CHCl₂ also included consideration of salting-out effects: The salting coefficient of NaCl on a natural log basis was determined to be 0.36 ± 0.06 M⁻¹, and this value was used for consideration of the salting-out effect of NaOH. Whereas the activation energy for CF₃CF₂CHCl₂ was greater than that for CF₃CHCl₂, the k_OH– value at 353 K of CF₃CF₂CHCl₂ was 10³ times larger than that of CF₃CHCl₂, indicating that reaction mechanisms for these two HCFCs differed from each other. The aqueous reaction of CF₃CF₂CHCl₂ with OH⁻ was found to proceed through dehydrofluorination on the basis of detection of CF₃CFCCl₂ as a primary degradation product of the reaction and proportionality of the rate constants to both concentrations of CF₃CF₂CHCl₂ and OH⁻.

Ammonia borane (AB; NH₃BH₃) is one of the most promising materials for hydrogen storage applications, mainly due to its high gravimetric hydrogen storage capacity of 19.6 wt%. In this paper, we present an exclusive kinetic analysis of AB thermolysis. Three methods are used for kinetic analysis of the thermal decomposition of AB, namely the Kissinger method, isoconversional model-free fitting method, and solid-state kinetics model–based method. Finally, a need to device a new model for thermal kinetics of AB was observed and hence a new kinetic model for AB thermolysis is proposed.

The autocatalytic oxidation of a weak acid is a common building block of the pH oscillators. These reactions can be described by a simple general scheme that includes a protonation equilibrium and the oxidation of the protonated form of the weak acid. Here we show that independently from the chemical nature of the oxidizing agent, these reactions bear some general features, namely (1) the change in pH (ΔpH) observed during the reaction is determined by the acidity constant (K_HA) and by the initial concentration of the unprotonated form of the weak acid (A⁻): , (2) the inflection time of the autocatalytic reaction (t_i) depends reciprocally on K_HA and on the initial hydrogen ion concentration, and (3) in the presence of a competitive reversible proton-binding component (D⁻), that is not involved in the oxidation process, ΔpH follows a titration-like curve as the concentration of D⁻ is increased, t_i is only slightly affected but the maximum rate of the autocatalytic process is significantly reduced. The slowing of the overall reaction is proportional to the acidity constant of the proton-binding component.

A kinetic study of the reaction of cardanol and maleic anhydride (MA) (mole ratios 1:0.25, 1:0.5, 1:0.75, 1:1) was carried out at five different temperatures ranging between 160 and 180°C with an interval of 5°C using paratoluene sulfonic acid (PTSA) as a catalyst. The acid values of the samples were checked at a regular time intervals to check the percentage of the completion of the reaction. The influence of the condensation temperature on the synthesized resins was studied using infrared spectroscopic analysis. The reaction between cardanol and MA was found to obey first-order rate kinetics. The specific rate constant (k) calculated by regression analysis was found to obey the Arrhenius expression. The thermodynamic parameters such as activation energy (E_a), frequency factor (Z), entropy (∆S), enthalpy (∆H), and free energy (∆G) were calculated. It was found that the reaction was spontaneous and irreversible. The experimental results were explained by proposing a reaction mechanism and deriving the rate equation.