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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.

Interactions between the cesium cation (Cs+) and humic substances were studied by the calculations of complexes between Cs+ and small ligand molecules mimicking different moieties in humic substances. The cesium cation gas-phase affinities (CsCAs) and basicities (CsCBs) of 52 model compounds (mainly aromatic) were calculated using the density functional method. The most common binding patterns of Cs+ are discussed. The CsCAs are mainly governed by ion-induced dipole p-type interaction (CsCA around 11 kcal/mol) in unsubstituted fused aromatic systems. The cesium cation tends to form a more localized type of bond in substituted aromatic compounds via the lone pairs of electronegative atoms (O, N) of substituents resulting in enhanced CsCA (around 20 kcal/mol). If the model compound is able to form chelate-type complexes with the Cs cation, CsCA may be even higher (20-28 kcal/mol). [ABSTRACT FROM AUTHOR]

The lithium-cation basicity (LCB=Gibbs energy of adduct dissociation) of methyl benzoate, and the three isomeric dimethyl phthalates (phthalate, iso- and tere-phthalate) has been determined by Fourier transform ion cyclotron resonance (FT-ICR), using the kinetic method. The dimethyl phthalate ester appears to be a relatively strong base toward Li+, as compared to the other isomers and to methyl benzoate. This is attributed to the chelation effect of the two carboxyl groups. The previously unknown protonic gas-phase basicity of dimethyl phthalate was also determined. Chelation makes also dimethyl phthalate a much stronger base than the two other isomers toward H+, but its protonated form decomposes readily by loss of a methanol molecule. [Copyright &y& Elsevier]

This work was dedicated to the characterization of the elemental composition of atmospheric particles associated with urban traffic. PM2.5 sampling campaigns were conducted in an urban road tunnel within the area of Nice: the Malraux tunnel. Samples were analyzed by ICP-MS-DRC for the determination of 16 metallic trace elements: Na, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Sr, Rb, Cd, Sn, Sb and Pb. An in depth study was carried out on the PM2.5 dataset collected with specific characterisation tools (enrichment factors, elemental ratio) and a receptor model: the Positive Matrix Factorization (PMF). The model showed that different profiles of emission could influence the ambient air of the tunnel and their contribution to the metal concentration in the air. Elemental fingerprints were used to attribute to each profile a specific emission source linked to road traffic. Finally, results showed that road traffic emissions could be divided into 3 main “subcategory” sources of emission: “soil resuspension” by automobile movement, “vehicular wear” and “fuel combustion”. [Copyright &y& Elsevier]

Humic substances (HS), including humic and fulvic acids, play a significant role in the fate of metals in soils. The interaction of metal cations with HS occurs predominantly through the ionized (anionic) acidic functions. In the context of the effect of HS on transport of radioactive cesium isotopes in soils, a study of the interaction between the cesium cation and model carboxylic acids was undertaken. Structure and energetics of the adducts formed between Cs+ and cesium carboxylate salts [Cs+RCOO−] were studied by the kinetic method and density functional theory (DFT). Clusters generated by electrospray ionization mass spectrometry from mixtures of a cesium salt (nitrate, iodide, trifluoroacetate) and carboxylic acids were quantitatively studied by CID. By combining the results of the kinetic method and the energetic data from DFT calculations, a scale of cesium cation affinity, CsCA, was built for 33 cesium carboxylates representing the first scale of cation affinity of molecular salts. The structural effects on the CsCA values are discussed. [Copyright &y& Elsevier]

The gas-phase basicity (GB) of the flexible polyfunctional N(1),N(1)-dimethyl-N(2)-beta-(2-pyridylethyl)formamidine (1) containing two potential basic sites (the ring N-aza and the chain N-imino) is obtained from proton-transfer equilibrium constant measurements, using Fourier-transform ion-cyclotron resonance mass spectrometry. Comparison of the experimental GB obtained for 1 with those reported for model amidines and azines indicates that the chain N-imino in the amidine group is the favored site of protonation. Semiempirical (AM1) and ab initio calculations (HF, MP2, and DFT), performed for 1 and its protonated forms, confirm this interpretation. These results are in contrast to those found previously for N(1),N(1)-dimethyl-N(2)-azinylformamidines (containing the amidine function directly linked to the azinyl ring), in which the ring N-aza is the most basic site in the gas phase. The separation of the two potential basic sites in 1 by the ethylene chain interrupts the resonance conjugation between the two functions and changes their relative basicities and, thus, the preferable site of protonation. It also increases the chelation effect against the proton and the gas-phase basicity of 1 in such a magnitude that consequently 1 may be classified as a superbase (GB = 241.1 kcal mol(-)(1)). A transition state corresponding to the internal transfer of the proton (ITP) between the ring N-aza and the chain N-imino in 1 is investigated at the DFT(B3LYP)/6-31G level. The energy barrier calculated for the ITP between the two basic sites is small and vanishes when zero-point vibrational terms and thermal corrections are applied to obtain the enthalpy or Gibbs energy of activation for the proton transfer. Additional calculations at the DFT(MPW1K)/6-31G level confirm this behavior. This indicates that the quantum-chemical ITP in 1 has a single-well character. The proton is located on the N-imino site, and the H-bond is formed with the N-aza site.