2,2′-Bipyridin-1-ium hemioxalate oxalic acid monohydrate

The asymmetric unit of the title compound, C10H9N2+·0.5C2O42−·C2H2O4·H2O, consists of a 2,2′-bipyridinium cation, half an oxalate dianion, one oxalic acid and one water molecule. One N atom in 2,2′-bipyridine is unprotonated, while the second is protonated and forms an N—H...O hydrogen bond. In the crystal, the anions are connected with surrounding acid molecules and water molecules by strong near-linear O—H...O hydrogen bonds. The water molecules are located between the anions and oxalic acids; their O atoms participate as donors and acceptors, respectively, in O—H...O hydrogen bonds, which form sheets arranged parallel to the ac plane

Influence of the Solvent on the Stability of Aminopurine Tautomers and Properties of the Amino Group

Amino derivatives of purine (2-, 6-, 8-, and N-NH2) have found many applications in biochemistry. This paper presents the results of a systematic computational study of the substituent and solvent effects in these systems. The issues considered are the electron-donating properties of NH2, its geometry, π-electron delocalization in purine rings and tautomeric stability. Calculations were performed in ten environments, with 1 2 proximity interactions depend on its position and the tautomer. The results show that they are the main factor determining how solvation affects the electron-donating strength and geometry of NH2. Proximity with the NH∙∙∙HN repulsive interaction between the NH2 and endocyclic NH group results in stronger solvent effects than the proximity with two attractive NH∙∙∙N interactions. The effect of amino and nitro (previously studied) substitution on aromaticity was compared; these two groups have, in most cases, the opposite effect, with the largest being in N1H and N3H purine tautomers. The amino group has a smaller effect on the tautomeric preferences of purine than the nitro group. Only in 8-aminopurine do tautomeric preferences change: N7H is more stable than N9H in H2O

N-Methyl-4-(4-nitrophenyl)-N-nitroso-1,3-thiazol-2-amine

The title compound, C10H8N4O3S, is almost planar [dihedral angle between the rings = 2.2 (2)°; r.m.s. deviation for the non-H atoms = 0.050 Å]. In the crystal, C—H...O and C—H...N hydrogen bonds link the molecules into (10-2) layers

Substituent Effect on the σ- and π‑Electron Structure of the Nitro Group and the Ring in <i>Meta</i>- and <i>Para</i>-Substituted Nitrobenzenes

An application of quantum chemical modeling allowed us to investigate a substituent effect on a σ and π electron structure of a ring and the nitro group in a series of <i>meta</i>- and <i>para</i>-X-substituted nitrobenzene derivatives (X = NMe₂, NHMe, NH₂, OH, OMe, Me, H, F, Cl, CF₃, CN, CHO, COMe, CONH₂, COOH, NO₂, and NO). The obtained pEDA and sEDA parameters (the π- and σ-electron structure characteristics of a given planar fragment of the system obtained by the summation of π- and σ-orbital occupancies, respectively) of the NO₂ group and the benzene ring allowed us to reveal the impact of the substituents on their mutual relations as well as to analyze them from the viewpoint of substituent characteristics. The decisive factor for dependence of pEDA on sEDA of the ring is electronegativity of the atom linking the substituent with the ring; in subgroups an increase of sEDA is associated with a decrease of pEDA. The obtained mutual relation between pEDA­(NO₂) and pEDA­(ring) characteristics documents strong resonance interactions for electron-donating substituents in the <i>para</i> position. The observed substituent effect on the σ-electron structure of the nitro group, sEDA­(NO₂), is significantly greater (∼1.6 times) for <i>meta</i> derivatives than for the <i>para</i> ones

Dependence of the Substituent Effect on Solvent Properties

The influence of a solvent on the substituent effect (SE) in 1,4-disubstituted derivatives of benzene (BEN), cyclohexa-1,3-diene (CHD), and bicyclo[2.2.2]­octane (BCO) is studied by the use of polarizable continuum model method. In all X–R–Y systems for the functional group Y (NO₂, COOH, OH, and NH₂), the following substituents X have been chosen: NO₂, CHO, H, OH, and NH₂. The substituent effect is characterized by the charge of the substituent active region (cSAR­(X)), substituent effect stabilization energy (SESE), and substituent constants σ or <i>F</i> descriptors, the functional groups by cSAR­(Y), whereas π-electron delocalization of transmitting moieties (BEN and CHD) is characterized by a geometry-based index, harmonic oscillator model of aromaticity. All computations were carried out by means of B3LYP/6-311++G­(d,p) method. An application of quantum chemistry SE models (cSAR and SESE) allows to compare the SE in water solutions and in the gas phase. Results of performed analyses indicate an enhancement of the SE by water. The obtained Hammett-type relationships document different nature of interactions between Y and X in aromatic and olefinic systems (a coexistence of resonance and inductive effects) than in saturated ones (only the inductive effect). An increase of electric permittivity clearly enhances communications between X and Y for BEN and CHD systems