A textbook case of twisted structure due to hydrogen-hydrogen steric clash, the biphenyl molecule, has been studied in real space from a new perspective. Long-term discrepancies regarding the origin of...

Stable dimers of protonated pyridine–boronic acid are found in the gas phase and solvent models. The importance of electrostatics is discussed.

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Carbon dioxide can form compounds with nitrogen heterocyclic carbenes (NHCs) based on azoles through noncovalent interactions or by covalent bonding. A narrow dependence on the carbene structure has been observed for the preference for one or the other type of bonding, as revealed by a series of physicochemical descriptors. In our survey, a set of NHCs based on the azole family (three classical, three abnormal, and one remote) was shown to bind CO2 at the accurate G4MP2 computational level. In most cases, exothermic reaction profiles towards the covalently bound form were found, which reached stabilization enthalpies of up to −77 kJ mol−1 for the remote carbene case. Both noncovalent and covalent minima and the corresponding transition state that connects them have been identified as stationary points along the reaction coordinate.

The ability of Be as a hydrogen bond acceptor has been explored by studying the potential complexes between this molecule and a set of hydrogen bond donors (HF, HCl, HNC, HCN, HO, and HCCH). The electronic structure calculations for these complexes were carried out at the MP2 and CCSD(T) computational levels together with an extensive NBO, ELF, AIM, and electrostatic potential characterization of the isolated Be system. In all the complexes, the Be-Be σ bond acts as electron donor, with binding energies between 19 and 6 kJ mol. A comparison with the analogous cyclopropane:HX complexes shows similar binding energies and contributions of the DFT-SAPT energetic terms. A blue-shift of the harmonic frequencies of Be is observed upon complexation.

Conventional bases become very strong acids upon association with alkaline-earth derivatives MX2 (M = Be, Mg and Ca).

Ab initio and DFT calculations have been carried out to study the reaction mechanism between diformylketene and formamide. Gas-phase calculations show that the mechanism is concerted in contrast to the results of a previous paper. However, although it appears there is one single transition state, the characteristics of its structure reveal a very asynchronous reaction mechanism. The reaction is clearly exothermic and as well has a rather small activation energy. Its pseudopericyclic character has been confirmed by calculation of magnetic properties. The effect of solvent has been analyzed by using the Onsager and PCM methods: substantial changes have not been found in solution.

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