Aggregation of 2-acylaminopyridines and their 6-methyl derivatives in chloroform solution was studied by (1)H, (13)C, and (15)N NMR spectroscopies. The results were compared with (13)C and (15)N CPMAS NMR and IR spectral as well as with X-ray structural data. Intermolecular interactions in solution and in solid state were found to have a similar nature. Relatively strong N(amide)-H···N(pyridine) intermolecular hydrogen bonds enable dimerization to take place. Steric interactions in N-pivaloyl- and N-1-adamantylcarbonyl as well as that caused by the 6-methyl group hinder formation of the dimeric aggregates stabilized by the N(amide)-H···N(pyridine) intermolecular hydrogen bonds. In general, the DFT optimized geometries of the aggregates in chloroform solution are in agreement with the X-ray crystal structures. Wavenumbers of the stretching vibration band of the C═O group were also found indicative of the type of hydrogen bond present in the solid state.

2-Ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate was polymerized in the presence of squarylium dye and various onium salts.

Intermolecular hydrogen bonds between 2,6-bis(acylamino)pyridines and dipyridin-2-ylamine as well as 4,4-dimethylpiperidine-2,6-dione are responsible for relatively strong interactions between these species. Association has been found to be significantly affected by the size of acyl substituent (chemical shift of the NH proton was used as the main probe in determination of the association constants). Calculations at the DFT level of theory are in line with the experimentally observed results. Calculated energies of the interactions between the complex congeners also show the size of the substituent to affect the association. Conformational changes in the dipyridin-2-ylamine molecule are shown to adapt a geometry suitable for formation of efficient hydrogen bonding.

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The 2-[1H]-pyridone/2-hydroxypyridine tautomeric pair and its 6-substituted complexes have been studied with the use of DFT(M05) method. The intermolecular interaction energy has been calculated and discussed in the light of secondary interaction concept. The attractive secondary interactions of O/NH and O/OH type and OH/NH and OH/OH repulsions have been analyzed in terms of stabilizing or destabilizing influence on intermolecular behavior. The transition states of the double proton transfer reaction have been found and the energy of activation has been determined. The activation energy of the proton transfer reaction, geometry of the complexes and transition states show NH(2) and/or OH groups influence the properties of complexes and transition states. The HOMA index of aromaticity was applied to describe the π-electron delocalization in the heterocyclic rings.

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