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Wetter is better: The direct arylation of thiazoles on water is quicker, cleaner, and higher‐yielding than arylation in organic solvents. The reaction works under mild conditions for an array of aryl iodides, producing 2,5‐diaryl thiazoles in excellent yields. Importantly, novel bi‐heteroaryl compounds are produced without the requirement for stoichiometric organometallic coupling agents.

In this work, we analyze a series of o-hydroxyaryl aldehydes to discuss the interrelation between the resonance-assisted hydrogen bond (RAHB) formation and the aromaticity of the adjacent aromatic rings. As compared to the nonaromatic reference species (malonaldehyde), the studied compounds can be separated into two groups: first, the set of systems that have a stronger RAHB than that of the reference species, for which there is a Kekulé structure with a localized double CC bond linking substituted carbon atoms; and second, the systems having a weaker RAHB than that of the reference species, for which only pi-electrons coming from a localized Clar pi-sextet can be involved in the RAHB. As to aromaticity, there is a clear reduction of aromaticity in the substituted ipso ring for the former group of systems due to the formation of the RAHB, while for the latter group of species only a slight change of local aromaticity is observed in the substituted ipso ring.

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The influence of various basis sets used in HF and DFT/B3LYP calculations to the values of atoms in molecules (AIM) parameters derived from the electron density distibution for weak hydrogen-bonded systems is investigated. Using three model complexes, F(3)CH...NH(3), F(3)CH...NCH, and FCCH...NH(3), we show that values of the most important AIM parameters calculated in the bond critical point of the H...N hydrogen bond are almost independent of both the method and the basis set. Only the smallest Dunning-type cc-pVDZ or aug-cc-pVDZ basis sets may lead to poor results, whereas even medium-sized Pople-type basis sets can give reasonable results converting to those obtained from the use of large Dunning-type basis sets.

Charge-assisted hydrogen bonds (CAHBs) of N-H···Cl, N-H···Br, and P-H···Cl type were investigated using advanced computational approach (MP2/aug-cc-pVTZ level of theory). The properties of electron density function defined in the framework of Quantum Theory of Atoms in Molecules (QTAIM) were estimated as a function of distance in H-bridges. Additionally, the interaction energy decomposition was performed for H-bonded complexes with different H-bond lengths using the Symmetry-Adapted Perturbation Theory (SAPT). In this way both QTAIM parameters and SAPT energy components could be expressed as a function of the same variable, that is, the distance in H-bridge. A detailed analysis of the changes in QTAIM and SAPT parameters due to the changes in H···A distance revealed that, over some ranges of H···A distances, electrostatic, inductive and dispersive components of the SAPT interaction energy show a linear correlation with the value of the electron density at H-BCP ρ(BCP). The linear relation between the induction component, E(ind), and ρ(BCP) confirms numerically the intuitive expectation that the ρ(BCP) reflects directly the effects connected with the sharing of electron density between interacting centers. These conclusions are important in view of charge density studies performed for crystals in which the distance between atoms results not only from effects connected with the interaction between atomic centers directly involved in bonding, but also from packing effects which may strongly influence the length of the H-bond.

The nature of a hydride-halogen bond is investigated by means of high-level quantum mechanical calculations expended with symmetry-adapted perturbation theory (SAPT), quantum theory of atoms in molecules (QTAIM), and natural bond orbital (NBO) methods. As model hydride-halogen bonded systems complexes between either LiH or HBeH and either XCF(3) or XCCH (X = F, Cl, Br, I) are used. It is shown that the formation of a hydride-halogen bond leads to the elongation of the R(δ+)-H(δ-) hydride bond, which is accompanied by the blue shift of the ν(R-H) stretching vibration frequency and the increase of the IR intensity of this mode. All these effects, although untypical in the case of, e.g., hydrogen bonds, can be considered as rather typical for hydride-halogen bonded systems. The decomposition of the interaction energy based on the SAPT method clearly indicates the dominant role of the induction term, thus the inductive nature of a hydride-halogen bond in opposition to previous findings. NBO-based analysis indicates the charge transfer from the hydride molecule to the more remote parts of the halogen donor and that the elongation of the R-H bond is caused by the charge outflow from the σ(RH) bonding orbital.

The interplay between aromaticity and hydrogen bonding in 1,3-dihydroxyaryl-2-aldehydes is investigated by means of quantum-chemical calculations. The position of the extra ring formed by substituents interacting through the hydrogen bond (HB) is found to influence both the strength of the HB and the local aromaticity of the polycyclic aromatic hydrocarbon (PAH) skeleton. The HBs are stronger and the entire system is energetically more stable when a kinked-like structure is generated by formation of the quasi-ring. Relatively greater loss of aromaticity of the ipso-ring can be observed for these kinked-like structures because of the larger participation of pi-electrons coming from the ipso-ring in the formation of the quasi-ring. We conclude that the quasi-ring partially adopts the role of a typical aromatic ring, the position of which has a meaningful influence on the aromaticity of the rest of the rings. This makes it possible to explain and modify the properties of 1,3-dihydroxyaryl-2-aldehydes by the planned substitution to the appropriate position of the given PAH.