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O-type variations on C-H bond dissociation energies were studied.

The first detailed thermodynamic analysis in terms of the driving forces for ach basic step for the nitric oxide (NO)-initiated reaction with 3,6-dibromocarbazolide is presented. It is shown that an electrophilic combination of NO with 3,6-dibromocarbazolide to form the incipient radical anion, followed by electron transfer from the latter to NO, represents the most feasible mechanism. Electron transfer from the electron-rich species to NO may be incorporated when the substrate is a better electron-providing species.

Research was conducted to examine the role of adjacent onium cations and remote substituents on the H-A+ bond equilibrium acidities in dimethyl sulfoxide solution. The study is an extension of previous investigation on ylide thermodynamic stability scale and its implication for the importance of resonance effect on ylide stabilities. Results suggest that part of the stabilization in the phosphonium and sulfonium ylide cases arises from the backbonding stabilization involving the o* and/or 3d orbital participation.

Equilibrium acidities in DMSO for phenylhydrazine, five p-substituted derivatives, 1,2-diphenylhydrazine and 1,1,2-triphenylhydrazine were measured. The bond dissociation enthalpies (BDEs) of their acidic N-H bonds were estimated. The alpha-N-H bonds in CHsub3CONHNHsub2, PhCONHNHsub2, NHsub2NHCOsub2Et and PhSOsub2NHNHsub2 hydrazides were more acidic than the alpha-N-H bonds in corresponding amides, and the BDEs were weaker.

Bond dissociation energies of the acidic C-H bonds in 13 alpha-substituted 9-mehtylanthracenes and 11 10-substituted methylanthracenes. This included equilibium acidity (pKHA), reduction potential Ere(HA), oxidation potential Eox(HA), and oxidation potential of conjugate anions Eox(A-) in dimethyl sulfoxide solution. Equilibrium acidities were linearly correlated with Hammettsigma negative constants. Combinations of equilibrium acidities were used to determine homolytic bond dissociation energies.

The delta G(sub hydride) (R+) data for some stable carbocations and less stable aromatic carbocations derived from substituted toluenes, fluorenes and 9-methylanthracenes are reported. The computation of hydride affinities of organic cations was based on two equations derived from thermochemical cycles. Linear correlations were observed between hydride affinities and solution electron affinities of hydride acceptors. Correlations between delta G(sub hydride)(R+) and pK(sub R+) of corresponding carbinols provide convenient estimates of each other as long as the other is known.

Bond dissociation energies and hydronium ion concentrations at equilibrium of benzylic carbon to hydrogen bonds in dimethyl sulfoxide are presented. Nineteen triphenylmethanes, three dihydroanthracenes and nine xanthenes were used in the experiment. The resonance effect due to the solvation of a substituent induced a conformational alteration to allow for conjugative overlap of the anion and the substituents. The effect of substituents far from the carbanion was found to be negligible.

A thermodynamic study of the cleavage of carbon-sulfur bonds involves the analysis of the enthalpies of reactions between six thiophenoxides and fiveresonance-stabilized carbenium ions. C-S bond cleavage is of interest in the environmentally-critical desulfurization of coal. A battery of calorimetric andvoltammetric tests yield correlated data on the heats of heterolysis and homolysis, redox potentials and heats of entropies of the various processes involved in the reactions. These are presented and discussed in detail.

N-heterocyclic phosphines (NHPs) have recently emerged as a new group of promising catalysts for metal-free reductions, owing to their unique hydridic reactivity. The excellent hydricity of NHPs, which rivals or even exceeds those of many metal-based hydrides, is the result of hyperconjugative interactions between the lone-pair electrons on N atoms and the adjacent σ*(P–H) orbital. Compared with the conventional protic reactivity of phosphines, this umpolung P–H reactivity leads to hydridic selectivity in NHP-mediated reductions. This reactivity has therefore found many applications in the catalytic reduction of polar unsaturated bonds and in the hydroboration of pyridines. This review summarizes recent progress in studies of the reactivity and synthetic applications of these phosphorus-based hydrides, with the aim of providing practical information to enable exploitation of their synthetically useful chemistry. [ABSTRACT FROM AUTHOR]

An efficient asymmetric allylation reaction of allylboronates with seven-membered cyclic imines, dibenzo[b,f][1,4]oxazepines, is described. The reaction, which is catalyzed by a Bi(OAc)3/CPA system, gives a range of chiral nitrogen-containing heterocycle structures in high yields and with good enantioselectivities. The conversion of these products to nitrogen-containing heterocycles is also demonstrated. [ABSTRACT FROM AUTHOR]

While many approaches to predict aqueous pKa values exist, the fast and accurate prediction of non‐aqueous pKa values is still challenging. Based on the iBonD experimental pKa database (39 solvents), a holistic pKa prediction model was established using machine learning. Structural and physical‐organic‐parameter‐based descriptors (SPOC) were introduced to represent the electronic and structural features of the molecules. The models trained with a neural network or the XGBoost algorithm showed the best prediction performance with a low MAE value of 0.87 pKa units. The approach allows a comprehensive mapping of all possible pKa correlations between different solvents and it was validated by predicting the aqueous pKa and micro‐pKa of pharmaceutical molecules and pKa values of organocatalysts in DMSO and MeCN with high accuracy. An online prediction platform was constructed based on the current model, which can provide pKa prediction for different types of X−H acidity in the most commonly used solvents. [ABSTRACT FROM AUTHOR]