Intramolecular N-H…X (X = F, Cl, Br, and I) hydrogen bonding patterns of aromatic amides in the solid state are summarized. It is revealed that the key for the formation of this kind of weak intramolecular hydrogen bonding in X-ray crystal structures is to suppress the competition of strong intermolecular N-H…O-C hydrogen bonding of the amide unit. For amides with identical backbones, the bonding capacity of halogen atoms as hydrogen bonding acceptors is in the order of F>Cl>Br>I, which is in accordance with their electronegativity strength. Generally, the five-membered hydrogen bonding is easier to form than the six-membered one.

N-H···X(X = F, Cl, Br, and I) hydrogen bonding in aromatic amide derivatives in crystal structures

N-phenyl-4-oxo-4H-2-chromone carboxamides were found to be inactive as MAO inhibitors in contrast with their N-phenyl-4-oxo-4H-3-chromone carboxamide isomers. In order to obtain a close insight into the docking mechanism for this family of compounds, the molecular and supramolecular structures of nine N-phenyl-4-oxo-4H-2-chromone carbox­amides were determined. It was found that, in most of the secondary structures, the N(amido) and the O(carboxyl) of the carboxamide residue participate in strong intramolecular interactions, with the O atom of the chromene ring and with the H(ortho)—C (phenyl), respectively. When the phenyl ring had accessible acceptors as substituents a third intramolecular hydrogen bond was also observed. As a consequence, rotations of the chromone and phenyl rings around the N—C(alpha) and C(alpha′)—C=O are constrained and the compounds were found to be more planar than would otherwise be expected. The deviation from planarity of the whole molecule can be quantified by the dihedral angles between mean planes of the aromatic rings and it was found that they were mainly affected by the degree of torsion of the phenyl ring with respect to the amide residue. The molecular conformations assumed by the secondary amides clearly contrast with that of a related tertiary amide that was also determined in this study. The unavailability of the N in this compound as a donor strongly influences the molecular isomerism and conformation. This analysis demonstrates that the molecules can be classified into four groups depending on the types of interactions formed as described above. If the secondary N(amido) of the carboximide is involved in two intramolecular interactions then this atom does not form any intermolecular contacts. In all other cases it does and the supramolecular structure formed is in most cases supplemented by weak C—H⋯O interactions.

Structural characterization of some N-phenyl-4-oxo-4H-2-chromone carboxamides.

2,7-Disubstituted-1,8-naphthyridine derivatives have been found to self-assemble into infinite 1-D tapes in the solid state in a manner similar to that seen previously for their 2,6-disubstituted pyridine analogues.

Self-assembly into infinite tapes by 2,7-disubstituted-1,8-naphthyridines in the solid state

Different tautomeric and zwitterionic forms of chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid) are present in the crystal structures of chelidamic acid methanol monosolvate, C(7)H(5)NO(5)·CH(4)O, (Ia), dimethylammonium chelidamate (dimethylammonium 6-carboxy-4-hydroxypyridine-2-carboxylate), C(2)H(8)N(+)·C(7)H(4)NO(5)(-), (Ib), and chelidamic acid dimethyl sulfoxide monosolvate, C(7)H(5)NO(5)·C(2)H(6)OS, (Ic). While the zwitterionic pyridinium carboxylate in (Ia) can be explained from the pK(a) values, a (partially) deprotonated hydroxy group in the presence of a neutral carboxy group, as observed in (Ib) and (Ic), is unexpected. In (Ib), there are two formula units in the asymmetric unit with the chelidamic acid entities connected by a symmetric O-H···O hydrogen bond. Also, crystals of chelidamic acid dimethyl ester (dimethyl 4-hydroxypyridine-2,6-dicarboxylate) were obtained as a monohydrate, C(9)H(9)NO(5)·H(2)O, (IIa), and as a solvent-free modification, in which both ester molecules adopt the hydroxypyridine form. In (IIa), the solvent water molecule stabilizes the synperiplanar conformation of both carbonyl O atoms with respect to the pyridine N atom by two O-H···O hydrogen bonds, whereas an antiperiplanar arrangement is observed in the water-free structure. A database study and ab initio energy calculations help to compare the stabilities of the various ester conformations.

Pseudopolymorphs of chelidamic acid and its dimethyl ester.

The title compound, C10H12ClNO2, is a halogenated derivative of a secondary amide bearing an aromatic substituent. The C(=O)—N(H)—Car—Car torsion angle of −33.70 (18)° rules out the presence of resonance spanning the amide as well as the aromatic system. In the crystal, classical N—H⋯O hydrogen bonds, as well as C–H⋯O contacts connect the mol­ecules into chains propagating along the a axis.

https://journals.iucr.org/e/issues/2011/11/00/zj2028/zj2028.pdf

3-Chloro-N-(4-meth-oxy-phen-yl)propanamide.

In the title compound, C15H14BrNO, N—H⋯O hydrogen bonds result in the formation of a chain parallel to the c axis.

N‐(2‐Bromo­phen­yl)‐2‐phenyl­propanamide

The title mol­ecule, C9H9NO4, possesses crystallographically imposed twofold rotation symmetry. In the crystal structure, the mol­ecules are stacked into ladders extended along the c axis, with a short inter­molecular O⋯C contact of 3.297 (2) A. The crystal packing is stabilized by carbonyl dipolar inter­actions and van der Waals forces.

Dimethyl pyridine-2,6-dicarboxylate

Dimethyl 2,3-dihydroxyterephthalate is an important intermediate widely used in the synthesis of 1H,4H-benzo[2,1b:3,4-b0]bisthiete and 2H,3H-benzo[1,2-b:4,3-b0]bisthiete, which are very versatile reagents for the generation of polycyclic sulfur-containing compounds (Meier & Rumpf, 1998; Meier & Mayer, 1994) and macrobicyclic Fe sequestering agents (Garrett et al.,1991). The title compound, (I), of which we report the crystal structure here, can also be used directly to synthesize enterobactin analogues (Weitl et al., 1981).

Dimethyl 2,3‐dihydroxyterephthalate

The title complex, C9H11NO3, was synthesized from dimethyl pyridine-2,6-dicarboxyl­ate. A single weak inter­molecular O—H⋯N hydrogen bond links mol­ecules into a one-dimensional zigzag chain.

Jian-Ying Huang

Papers

N‐(2‐Bromophenyl)‐2‐phenylpropanamide

Dimethyl pyridine-2,6-dicarboxylate

Dimethyl 2,3‐dihydroxyterephthalate

Ethyl 6‐(hydroxymethyl)picolinate

Jian-Ying Huang

Papers

N‐(2‐Bromo­phen­yl)‐2‐phenyl­propanamide

Dimethyl pyridine-2,6-dicarboxylate

Dimethyl 2,3‐dihydroxyterephthalate

Ethyl 6‐(hydroxymethyl)picolinate

N‐(2‐Bromophenyl)‐2‐phenylpropanamide