On structural and spectroscopic differences between quinoline‐2‐carboxamides and theirN‐oxides in the solution and solid state

Abstract

Intramolecular hydrogen bonding in the primarily and secondarily substituted quinoline‐2‐carboxamides and their N‐oxides has been studied in the solution by multinuclear NMR spectroscopy. Hydrogen bonding patterns and supramolecular arrangement in the solid state have been determined by single crystal X‐ray analysis. In quinoline‐2‐carboxamides weak, nonlinear intramolecular NH…N hydrogen bond is present, but in the solid state the intermolecular hydrogen bonds and packing forces are the factors that decide on the properties of 3D structures. In quinoline‐2‐carboxamide N‐oxides the most important structural features are the intramolecular hydrogen bonds. Details of different weak interactions and resulting 3D arrangement of molecules are discussed.In the solution, two separate 1H signals are observed for the primary quinoline‐2‐carboxamides in the range from ca. 5.8 to 8.1 ppm. The chemical shifts of the NH group's proton for studied R′‐quinoline‐2‐R‐carboxamides are in the range from 8.1 to 8.4 ppm. For the N‐oxide of 4‐R′‐quinoline‐2‐carboxamides (R′ = H, Me, OPh, Cl and Br), the values of the proton chemical shifts of the NH group in the range from 10.78 to 11.38 ppm (for primary amides) indicating that this group forms hydrogen bonds with the oxygen of the N‐oxide group. This bond is stronger than the NH…N bond in quinoline‐2‐carboxamides. For the secondary amide N‐oxides, the δ(NH) values are increasing from 11.25 to 11.77 ppm in the sequence of substituents 4‐Br < 4‐Cl < 4‐H < 4‐Me < 4‐OPh. For 4‐substituted compounds these values depend also on the substituent effect. Copyright © 2009 John Wiley & Sons, Ltd.

N–H⋯O versus O–H⋯O: density functional calculation and first principle molecular dynamics study on a quinoline-2-carboxamide N-oxide

“…This compound possesses a resonance-assisted N–H⋯O H-bond (see Fig. 1 ) confirmed experimentally in 2009 by Kamiński et al [ 12 ]. Previous studies of quinoline-2-carboxamides and their N-oxides from the 1970s to 1980s excluded the existence of the intramolecular N–H⋯N H-bond in the primary quinoline-2-carboxamides [ 13 , 14 ], while a recent study [ 12 ] described the N–H⋯N contacts as very weak, non-linear H-bonds, weak enough to be not decisive in the formation of structural motifs in the crystal (intermolecular H-bonds were found to be more important [ 12 ]).…”

“…However, the N-oxide function strengthens the intramolecular H-bond significantly, making it the primary structural factor in the solid state. For example, molecules belonging to the secondary carboxamides were connected only by weak intermolecular contacts [ 12 ]. Therefore, following recent findings related to H-bonding presence and character, the current report presents computations based on static and molecular dynamics models to shed more light on the presence and dynamics of H-bonds.…”

“…The computations in two phases allowed a more detailed study of the mobility of the bridge proton and its influence on the molecular features of the investigated N-oxide. Ab initio MD was employed to analyze not only metric parameters as a function of time, but also to draw a picture of spectroscopic features to make some comparisons with available experimental data [ 12 ]. Therefore the main aims of this work cover aspects related to the metric and spectroscopic parameters of time-evolution in picosecond time-scale obtained from CPMD simulations.…”

Estudio estructural de interacciones intra- e intermoleculares basadas en puentes de hidrógeno en piridin-2,6-dicarboxamidas

“…Por lo anterior, la estructura de las amidas puede ser descrita por los rotámeros E,Z cuando los sustituyentes en el átomo de nitrógeno son diferentes, (Gonzaĺez et al, 2015) figura 3. Los datos cristalográficos obtenidos para amidas muestran que el átomo de nitrógeno es plano, reforzando la existencia de los equilibrios mostrados en las figuras 1 y 2, (Kaminski et al, 2009) y de la isomería E,Z. Para amidas secundarias como las que se encuentran contenidas en péptidos y proteínas el isómero E es el más favorecido energéticamente.…”

“…Para amidas secundarias como las que se encuentran contenidas en péptidos y proteínas el isómero E es el más favorecido energéticamente. Sin embargo, es necesario resaltar que el predominio de isómeros depende, además, de la agregación molecular y de las interacciones por enlaces por puente de hidrógeno que pueden estar presentes en el empaquetamiento cristalino y en solución (Kaminski et al, 2009;Özdem et al, 2012). …”