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AbstractThis Glossary contains definitions, explanatory notes, and sources for terms used in physical organic chemistry. Its aim is to provide guidance on the terminology of physical organic chemistry, with a view to achieving a consensus on the meaning and applicability of useful terms and the abandonment of unsatisfactory ones. Owing to the substantial progress in the field, this 2021 revision of the Glossary is much expanded relative to the previous edition, and it includes terms from cognate fields.

Computational quantum chemistry has been employed to examine the production of ethylene with methanol-tohydrocarbon (MTH) processes via a carbon pool mechanism. We find that the M05-2X functional performs well for the types of reactions that are involved. The methylation reactions of the aromatic cocatalyst are the most energy-demanding steps in the process. For the subsequent production of [C.sub.2][H.sub.4], we have identified a low-energy pathway that involves multiple methyl shifts, followed by concerted deprotonation and [C.sub.2][H.sub.4] elimination. The substitutions of the Al and Si atoms in the participating Si-OH-Al moiety of zeolite catalysts with Ga and Ge do not lead to lower barriers for the methylation reactions, nor does the use of a more electron-rich aromatic cocatalyst. However, we find that the use of two cocatalysts, a nucleophile and an aromatic carbon pool, can provide an overall low-energy pathway for the MTH process. Key words: methanol-to-hydrocarbon (MTH) process, zeolite catalysis, computational chemistry. On a fait appel a des calculs de chimie quantique impliquant un meecanisme de mise en commun du carbone pour examiner la production d'ethylene par le procede du methanol a hydrocarbure (MAH). On a trouvee que la fonctionnelle M05-2X donne de bons resultats pour les types de reactions impliques. Les reactions de methylation de la portion aromatique du cocatalyseur sont les etapes qui requierent le plus d'energie. Pour la production subsequente du [C.sub.2][H.sub.4],ona identified une voie de basse eenergie qui implique de multiples deeplacements de groupes methyles, suivis d'une deprotonation concertee avec une elimination de [C.sub.2][H.sub.4]. Les substitutions des atomes d'aluminium et de silicium de la portion Si-OH-Al participante des catalyseurs comportant du Ga et du Ge ne conduit pas a des barrieres energeetiques inferieures pour les reactions de methylation et c'est aussi le cas lorsqu'on utilise un cocatalyseur aromatique plus riche en electron. Toutefois, on a trouvee que l'utilisation de deux cocatalyseurs, un nucleophile et une mise en commun de carbones aromatiques, peut conduire a une voie de faible eenergie globale pour le procede du MAH. Mots-cles: procede; du methanol a hydrocarbure (MAH), catalyseur de zeolite, calculs de chimie quantique. [Traduit par la Redaction], Introduction The limited supply of crude oil and the adverse environmental impact of its combustion have led to an increasing interest in alternative sources of energy. One of the most [...]

Thermodynamic and kinetic properties relating to hydrogen abstraction by methyl radical from various sites in polycyclic aromatic hydrocarbons (PAHs) were studied. It was found that the congested sites in the PAHs correspond to lower reaction enthalpy values, largely reflecting the release of steric strain upon creation of the radical.

The reaction enthalpy (298 K), barrier (0 K), and activation energy and preexponential factor (600-800 K) is examined computationally for the abstraction of hydrogen from benzene by the methyl radical, to assess their sensitivity to the applied level of theory. Inspection of the theoretically calculated rate parameters reveals a minor dependence on the level of theory for the preexponential factor.

The collision-induced dissociation (CID) reactions of a series of complexes of the type [[[Cu.sup.II](terpy)(AA)].sup.2} and [[Fe.sup.III](salen)-(AA)].sup.} (where terpy = 2,2':6',2''-terpyridine, AA= one of the twenty common amino acids, salen= N,N'-ethylenebis(salicylidencaminato)) are presented. The complexes undergo loss of the neutral amino acid in all cases, although the radical cation of arginie is also produced and its subsequent fragmentation examined.

Geometric parameters, atomization energies, and heats of formative are calculated for a series of small calcium-containing molecules using high-level quantum chemical methods. The W2C-best heats of formation are generally in good agreement with experimental values however there are discrepancies for a small number of molecules.

The binding energies of alkali metal monocations and alkaline-earth metal dications to a series of small oxygen and nitrogen bases is evaluated by means of CCSD(T) calculations on B3-LYP optimized structures. Conclusions reveal that although the neutral, ion interaction energy for alkali and alkaline-earth metal cations is dominated by electrostatic contributions, in many cases the correct basicity trends are only attained once polarization effects are also included in the model.

Ab initio molecular orbital calculations is employed to investigate the interactions between a set of basic substrate (B) with H(super +) and HF and the interaction between acids of varying strength (AH(super +)) with two bases, vinylamine and furan. The preferred site for protonation of the substrates appears to be determined primarily by the ability of the protonated species (BH(super +)) to delocalize the acquired positive charge.

Ab initio molecular orbital theory was employed to study base-catalyzed hydrogenation, to better understand and to rationalize the limitations of the catalytic reaction. A good balance between polarity and catalyst solubility is required in selecting the optimum solvent for the base-catalyzed hydrogenation reaction.

Peptidylglycine alpha-amidating monooxygenase catalyzes the biosynthesis of peptide hormones through radical cleavage of the C-terminal glycine residues of the corresponding prohormones. Ab initio calculations of radical stabilization energies and studies of free radical bromiations are correlated to identify classes of inhibitors o the enzyme.

The performance of a selection of theoretical procedures in describing the binding of Ca(super 2+) to ammonia and formaldehyde was assessed. Ca(super 2+) was predicted to bind more strongly to formaldehyde than to ammonia, in contrast to the ordering of proton and Li(super +1) affinities for the two molecules.

N-H bond dissociation energies (BDEs) and radical stabilization energies (RSEs) associated with the .NHCF3, .NHCHO, .NHCOCH3 and .NHCONH2 radicals are calculated at a number of theoretical levels. The performance of the various levels of theory in calculating the BDEs and RSEs of the NHX radicals are assessed.

High-level ab initio calculations of the barriers, exothermicities, and rate constants are performed for addition to alkenes and alkynes. The calculations confirmed that the reactions are contrathermodynamic, with addition to the alkene being favored despite the alkyne addition having the greater exothermicity.

Ab initio calculations are used to design radical-resistant amino acid residues. The steric repulsion between the amide carbonyl groups and the side chains of proteinogenic amino acid residues decreases the stability and ease of formation of alpha-carbon-centered peptide radicals.

The performance of a series of theoretical methods, for the calculation of bond dissociation energies and radical stabilization energies, against benchmark W1' and CBS-RAD values is assessed. Most of the substituents examined stabilized a methyl radical center with the exception of the perfluroalkyl substituents, CF3 and CF2CF3.

A new study of carbomethoxychlorocarbene and related carbonyl and halogenocarbenes uses high-level ab initio calculations at the G3(MP2)//B3-LYP level.

Research is presented describing the study of zeolite catalyzed hydrogenation of prototypical doubly bonded systems using the B3-LYP/6-311+G(3df,2p)//B3-LYP/6-31G(d) procedure.

An investigation of the impact of a range of theoretical methods and basis sets on the calculated geometry and dimerization energy of the acetylene-ammonia dimer HCCH...NH3 is presented.

Research has been conducted on the ligand-exchange reactions between phosphenium ion mono-adducts and simple first- or second-row Lewis bases. The feasibility of the ligand-exchange reactions is discussed.

G2-based methods were used to determine structure and heat formation of alkali and alkaline earth oxides and hydroxides.

Research was conducted to examine the reactions catalyzed by the B12-dependent enzyme diol dehydratase by means of ab initio molecular orbital theory. The calculations reveal that the radical rearrangement step is largely assisted by partial protonation of the migrating hydroxyl group. The application of the partial-proton-transfer concept makes a substantial contribution to the understanding of the mechanism of action of diol dehydratase. Results confirm that the enzyme is likely to use a suitable hydrogen-bond donor to bind the migrating hydroxyl group to the substrate.

The effect of interaction with a range of neutral molecules (X) on the barriers to the degenerate proton-transport reactions in NNH+ (X = Ar, HF, CO, N2, H2O) and methyl cation-transport reactions in NNCH3+ (X = HF, H2, H2, HCl, H2O) has been investigated. High-level ab initio calculations were performed using the G2** and G2(ZPE = MP2) methods. The results showed that the barriers to both and proton and methyl cation transport are lowered from their values in isolated ions by interaction with species that have values of the proton or methyl cation affinity lower than that of molecular nitrogen.

A study was conducted to analyze the coenzyme-B12-dependent rearrangement of 2-methyleneglutarate to (R)-3-methylitaconate catalyzed by 2-methyleneglutarate mutase. Ab initio molecular orbital theory was utilized to carry out the analysis. A transient fragmentation of the substrate after recombination of the fragments was examined. Results indicated that a cyclization/ring-opening mechanism needed less energy than the fragmentation and recombination mechanism.

A variety of high level ab initio calculations to investigate the heat of formation of the tert-butyl radical and the heats of formation of the tert-butyl cation and isobutene. The proton affinity of isobutene and the ionization energy of the tert-butyl radical were also estimated. The theoretical values of heat of formation of the tert-butyl radical, tert-butyl cation and isobutene were found to be 3-6 kJ mol-1 higher than the most recent estimates and these calculations are in good agreement with experiment.

The kinetics of ring opening are minimally influenced by heterosubstitution by nitrogen at the 1-position, whereas heterosubstitution by nitrogen or oxygen at the 2-position results in a significant rate enhancement for an already rapid reaction. In both cases, thus, the kinetically favored ring-opening pathway is not expected to lead to the thermodynamically preferred products. These were found in an examination of the ring opening of the cyclopropylcarbinyl radical and its N- and O-substituted analogues. The hybrid density functional method B3-LYP performs well for geometry- and frequency-dependent quantities.

Tests of the G2, G2(//QCI), CBS-Q and CBS-RAD-(QCISD, B3LYP) levels of theory have produced thermochemical data that are accurate within 10 kJ mol-1. These levels were applied to the analysis of the heats of formation of four C2H3N molecules and the C2H2N cations cyanomethyl, isocyanomethyl and azirinyl. Discrepancies higher than the 10 kJ mol-1 accuracy standard were observed in theoreticala and experimental results for the heats of formation of the radicals and cations.

The potential energy surface for fragmentation and rearrangement of {CH3CH2OCH2}+ was characterized using high level ab initio computations implemented at the G2 level. The ion-neutral complexes are important in the lowest-energy decomposition that result in the removal of water. The values obtained from RRKM computations on the G2 surface agreed well with experimental values obtained for metastable ion elimination products as well as findings of different deuterium- and 13C-labeling studies.

Research was conducted to characterize the potential energy surface for the reactions of phosphirenium or phosphiraniuim ions with acetylene or ethylne using ab initio molecular orbital calculations at the G2 level of theory. Detailed comparisons between competing exchange and insertion pathways confirm that the former is the kinetically favored process despite a large thermodynamic preference for insertion.

The effect of deprotonation at carbon on the stability, structure and thermochemistry of molecules and free radicals was investigated using the G2 ab initio method. To this end, a series of prototypical substituted methanes, CH3X, and free radicals, *CH2X, was examined, where X represents several substituents including the pi-donor groups NH2, OH, OCH3, SH, PH2, Cl, F and Br as well as the pi-acceptor groups BH2 and AlH2 and CHO, CN, NO2 and NC. It was shown that CH3X and *CH2X can be deprotonated to form carbon-centered anions CH2X(super -) and radical anions HCX(super *-), respectively.

Prototype radical addition reactions are studied using ab initio molecular orbital calculations at various levels of theory to determine a level of theory for predicting reliable barriers. It is shown that the use of QCISD/6-31G(d) or B3-LYP/6-31G(d) geometries is preferable to UHF/6-31G(d) or UMP2/6-31G(d) geometries. Calculations at the QCISD(T)/6-311+G(3df,2p) level on QCISD(T)/6-31G(d) geometries with B3-LYP/6-31G(d) ZPVEs also yield barriers for radical addition reactions to alkenes that are higher than those from solution-phase experimental data.

The consequences of protonation on the geometries and stabilization energies of prototypical *CH2X radicals (X = NH2, OH, OCH3, PH2, SH, F, Cl, Br, CN, CHO and NO2) were investigated through ab initio molecular orbital computations at the G2 level. For pi-donor substituents (X = NH2, OH, OCH3, PH2, SH, F, Cl and Br), protonation at X resulted into considerable +C :XH character for both CH3XH+ and *CH2XH+.