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Hydrogen bonds (HB) are arguably the most important noncovalent interactions in chemistry. We study herein how differences in connectivity alter the strength of HBs within water clusters of different sizes. We used for this purpose the interacting quantum atoms energy partition, which allows for the quantification of HB formation energies within a molecular cluster. We could expand our previously reported hierarchy of HB strength in these systems (Phys. Chem. Chem. Phys., 2016, 18, 19557) to include tetracoordinated monomers. Surprisingly, the HBs between tetracoordinated water molecules are not the strongest HBs despite the widespread occurrence of these motifs (e.g., in ice Ih). The strongest HBs within H2O clusters involve tricoordinated monomers. Nonetheless, HB tetracoordination is preferred in large water clusters because (a) it reduces HB anticooperativity associated with double HB donors and acceptors and (b) it results in a larger number of favorable interactions in the system. Finally, we also discuss (a) the importance of exchange‐correlation to discriminate among the different examined types of HBs within H2O clusters, (b) the use of the above‐mentioned scale to quickly assess the relative stability of different isomers of a given water cluster, and (c) how the findings of this research can be exploited to indagate about the formation of polymorphs in crystallography. Overall, we expect that this investigation will provide valuable insights into the subtle interplay of tri‐ and tetracoordination in HB donors and acceptors as well as the ensuing interaction energies within H2O clusters. [ABSTRACT FROM AUTHOR]

We used our recently proposed acidity–basicity interplay (ABI) model (Chem. Sci., 2018, 9, 4402) and the Jorgensen secondary interactions hypothesis (JSIH) to rationalise the experimentally observed trends in the formation constants of doubly and triply H-bonded systems with –NH…O=C– and –NH…N– interactions. Unlike the JSIH, the ABI interpretation can explain the trends in the complexation of amide/imide homo- and heterodimers as well as ADA–DAD clusters. We found that the strongest H-bonds play a very important role, a condition which offers an alternative to the well established JSIH to modulate the stability of these relevant systems. [ABSTRACT FROM AUTHOR]

Abstract We report an easy method to estimate relative hydrogen bond basicities of amides and imides in chloroform via 1H NMR experiments. We established hydrogen acceptor capacities of the studied compounds through their effect on the C H signal of the residual non-deuterated CDCl 3. The measurements correlate very well with DFT proton affinity energies. Overall, we present an easy and direct method for this particularly intricate determination. Graphical abstract Image 1 Highlights • Straightforward measure of hydrogen bond basicity of amides and imides. • 1H NMR estimation of relative basicity in chloroform. • Suitable determination of relative hydrogen bond basicities supported by theoretical and other experimental data. [ABSTRACT FROM AUTHOR]