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The concept of stoichiometrically unique reactions referred to as response reactions (RERs), earlier deduced by us in applications of chemical thermodynamics and kinetics, is extended to isodesmic reactions. Namely, it is shown that the additional stoichiometric constraints according to which the number and type of chemical bonds in a multiple chemical reaction system are conserved may be formally appended to the conventional RERs formalism. As a result, one can define and generate a stoichiometrically unique class of isodesmic RERs. Along with the conventional RERs, the newly defined isodesmic RERs are shown to be effective in converting the total enthalpies of the species obtained from ab initio calculations into accurate values of the standard enthalpies of formations for large species.

Geometry optimizations and fragmentation energies of the series of hydrogen cyanide borane(1) oligomers (up to hexamers) and their dehydrogenated analogues are presented. Structural parameters are examined at different computational levels:  MBPT(2) (second-order many-body perturbation theory), SDQ-MBPT(4) (fourth-order many-body perturbation theory limited to singly-, doubly-, and quadruply excited configurations), and DFT-B3LYP (density functional theory with Becke's three-parameter hybrid functional using the Lee−Yang−Parr correlation functional). These oligomers seem to be suitable input for the models of the polymer chain because of their periodic structure emerging from successive HCNBH or HCNB addition. The stability of the oligomers in terms of initial “cracking” of the weakest bond is fairly high, ranging from 97 to 443 kJ/mol for the HCNBH series and from 329 to 589 kJ/mol for the HCNB series.

Accurate experimental enthalpies of formation measured using static bomb combustion calorimetry, the “vacuum sublimation” drop calorimetry method, and the Knudsen-effusion method are reported for the first time for four azoles:  1-methylimidazole (1MeIMI), 1-methylpyrazole (1MePYR), 1-benzylimidazole (1BnIMI), and 1-benzylpyrazole (1BnPYR). These values and those corresponding to imidazole (1HIMI), pyrazole (1HPYR), 1-ethylimidazole (1EtIMI), 1-ethylpyrazole (1EtPYR), 1-phenylimidazole (1PhIMI), and 1-phenylpyrazole (1PhPYR) are compared with theoretical values using the G2(MP2) and the B3LYP/6-311*G(3df,2p)//6-31G(d) approaches. In general, there is a very good agreement between calculated and experimental values for the series of N-substituted imidazoles, while the agreement is less good for the series of the N-substituted pyrazoles. Experimentally, the gap between the enthalpies of formation of imidazoles and pyrazoles decreases significantly upon N-substitution, while the theoretical estimates indicate that this decrease is smaller.

In contrast to 1,3-butadiene, the textbook example of “conjugation stabilization”, G3(MP2) calculations yielding the enthalpy of hydrogenation ΔhydH²⁹⁸ of 1,3-butadiyne indicate that it is not stabilized by the conjugated configuration of its triple bonds. Differences between ethylenic and acetylenic π bonds are examined in the light of CAS-MCSCF calculations on 1,3-butadiene and 1,3-butadiyne.

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Ab initio calculations are performed for the electronic ground states and selected excited states of HeXn+ and the calculated bonding properties are discussed in terms of donor‐acceptor interactions between neutral He as the donor and the Xn+ cation as the acceptor.

The trends in the dissociation energies calculated for NeX+ and ArX+ are compared with those previously determined for HeX+ and discussed in terms of donor‐acceptor interactions between the weak electron donors Ne and Ar and the electron acceptors X+.

The effects of anellation (benzene → naphthalene → anthracene or pyrrole → indole, e.g.) on proton affinities are studied by measurements of gas‐phase acidities and theoretical (AM1) calculations for a wide range of parent compounds such as benzene, pyridine, cyclopentadiene, cycloheptatriene, and their anellated derivatives.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A thermochemical definition of aromaticity and homoaromaticity is based on the fact that the species of interest with its array of conjugated (homoconjugated) double bonds is thermodynamically more stable than its nonconjugated (nonhomoconjugated) analogues.