2-Acylamino-6-pyridones: Breaking of an Intramolecular Hydrogen Bond by Self-association and Complexation with Double and Triple Hydrogen Bonding Counterparts. Uncommon Steric Effect on Intermolecular Interactions

Abstract

2-Acylamino-6-pyridones (acyl = RCO, where R = Me, Et, i-Pr, t-Bu, and 1-adamantyl) were previously characterized by X-ray diffractometry and solid-state NMR techniques by us. One of these compounds was used recently in organocatalysis. The series is now studied in solution and by computational methods recommended for noncovalent interactions (DFT/M05). These compounds showed interesting behavior during dilution and titration experiments monitored by (1)H NMR. 2-Acylamino-6-pyridones change their conformation at higher concentrations, forming double hydrogen-bonded dimers and trimers in which an uncommon steric effect is observed. To the best of our knowledge, this is the first example of such behavior of hydrogen-bonded molecules. Heterocomplexation of the studied compounds happens via double or triple hydrogen bonding, depending on the properties of the counterpart. The computation data support and explain the effects observed experimentally, including the tautomeric, closed/open form equilibrium and intermolecular interaction preferences.

The influence of CH bond polarization on the self-association of 2-acylaminopyrimidines by NH/CH···O/N interactions: XRD, NMR, DFT, and AIM study

“…Moreover, the same approach has been used to study the hydrogen bond bridges in which the hydrogen bond acceptor carries three (FHÁÁÁFF [58], NHÁÁÁF, CHÁÁÁF [59]), two (NHÁÁÁO, or OHÁÁÁO [54]), and one lone electron pair (FHÁÁÁNH 3 [59]). This method have also been used in explaining the properties of intramolecular hydrogen bonds (NHÁÁÁN [60]) and intermolecular ones that stabilize dimer, trimers and tune the properties of rotamers in supramolecular assemblies [16,61]. It is fair to mention that we used this approach to highlight the differences in energy of interactions between NHÁÁÁN/O and CHÁÁÁN/O contacts, while the QTAIM was shown to be applicable for many structures where the hydrogen bonding is described as purely non-covalent interaction (even a weak one [62]) or it is considered as partially covalent one with relatively high bond orders [63].…”

Modulation of Conformational Preferences of Heteroaromatic Ethers and Amides through Protonation and Ionization: Charge Effect

“…Similarly, as shown in Figure (d), the strong repulsion between the positive H methyl (+0.208) and the positive hetero‐S atom (+0.439) is contradictory to the syn preference of 2‐[5]1S + 30 b . In fact, besides of the electrostatic factor, it has been found that the repulsion and steric effects within molecules act in similar way but cause quite opposite effects. So, the steric and quantum factors also need to be considered.…”

Substituent effects in hydrogen bonding: DFT and QTAIM studies on acids and carboxylates complexes with formamide

“…The M05 functional suggested for non-covalent interactions [40, 41] was used together with the 6-311+G(2d,2p) basis set as in previous publications [18, 21, 22]. The use of the diffuse functions is crucial for describing the anionic specie, while polarization functions are used to properly describe the hydrogen bonding.…”

“…The use of the diffuse functions is crucial for describing the anionic specie, while polarization functions are used to properly describe the hydrogen bonding. Optimizations were performed with the use of PCM model of solvation [42] in chloroform since in previous publications such treatment was in agreement with experimental results [18, 21, 22]. For all optimized structures the frequency calculations were ran to check if the geometry is in energy minima (only positive frequencies were obtained).…”