Two trans‐4‐aminoazoxybenzenes

Two isomeric trans‐4‐amino­azoxy­benzenes, trans‐1‐(4‐amino­phenyl)‐2‐phenyl­diazene 2‐oxide (α, C₁₂H₁₁N₃O) and trans‐2‐(4‐amino­phenyl)‐1‐phenyl­diazene 2‐oxide (β, C₁₂H₁₁N₃O), have been characterized by X‐ray diffraction. The α isomer is almost planar, having torsion angles along the C_aryl—N bonds of only 4.9 (2) and 8.0 (2)°. The relatively short C_aryl—N bond to the non‐oxidized site of the azoxy group [1.401 (2) Å], together with the significant quinoid deformation of the respective phenyl ring, is evidence of conjugation between the aromatic sextet and the π‐electron system of the azoxy group. The geometry of the β isomer is different. The non‐substituted phenyl ring is twisted with respect to the NNO plane by ca 50°, whereas the substituted ring is almost coplanar with the NNO plane. The non‐oxidized N atom in the β isomer has increased sp³ character, which leads to a decrease in the N—N—C bond angle to 116.8 (2)°, in contrast with 120.9 (1)° for the α isomer. The deformation of the C—C—C angles (1–2°) in the phenyl rings at the substitution positions is evidence of the different character of the oxidized and non‐oxidized N atoms of the azoxy group. In the crystal structures, mol­ecules of both isomers are arranged in chains connected by weak N—H?O (α and β) and N—H?N (β) hydrogen bonds.     

Three polymorphs of 4‐4′‐diiodobenzalazine,and 4‐chloro‐4′‐iodobenzalazine

Three polymorphs of 4,4′‐diiodobenzalazine (systematic name: 4‐iodobenzaldehyde azine), C₁₄H₁₀I₂N₂, have crystallographically imposed inversion symmetry. 4‐Chloro‐4′‐iodobenzalazine [systematic name: 1‐(4‐chlorobenzylidene)‐2‐(4‐iodobenzylidene)diazane], C₁₄H₁₀ClIN₂, has a partially disordered pseudocentrosymmetric packing and is not isostructural with any of the polymorphs of 4,4′‐diiodobenzalazine. All structures pack utilizing halogen–halogen interactions; some also have weak π (benzene ring) interactions. A comparison with previously published methylphenylketalazines (which differ by substitution of methyl for H at the azine C atoms) shows a fundamentally different geometry for these two classes, namely planar for the alazines and twisted for the ketalazines. Density functional theory calculations confirm that the difference is fundamental and not an artifact of packing forces.     

Two polymorphs of 2‐(4‐chlorophenyl)‐4‐methylchromenium perchlorate

Crystallization (from ethyl acetate solution) of 2‐(4‐chlorophenyl)‐4‐methylchromenium perchlorate, C₁₆H₁₂ClO⁺·;ClO₄⁻, (I), yields two monoclinic polymorphs with the space groups P2₁/n [polymorph (Ia)] and P2₁/c [polymorph (Ib)]; in both cases, Z = 4. Cations and anions, disordered in polymorph (Ib), form ion pairs in both polymorphs as a result of Cl—O...π interactions. Related by a centre of symmetry, neighbouring ion pairs in polymorph (Ia) are linked viaπ–π interactions between cationic fragments, and the resulting dimers are linked through a network of C—H...O(perchlorate) interactions between adjacent cations and anions. The ion pairs in polymorph (Ib), arranged in pairs of columns along the a axis, are linked through a network of C—H...O(perchlorate), C—Cl...π, π–π and C—Cl...O(perchlorate) interactions. The aromatic skeletons in polymorph (Ia) are parallel in the cationic fragments involved in dimers, but nonparallel in adjacent ion pairs not constituting dimers. In polymorph (Ib), these skeletons are parallel in pairs of columns, but nonparallel in adjacent pairs of columns; this is visible as a herring‐bone pattern. Differences in the crystal structures of the polymorphs are most probably the cause of their different colours.     

trans‐4‐[4‐(Dimethylamino)phenyl­iminomethyl]‐N‐phenylpyridinium hexafluorophosphate

The crystal structure of the dipolar chromophoric title compound, C₂₀H₂₀N₃⁺·PF₆^?, is described. The phenyl­ene and pyridyl rings are almost coplanar [dihedral angle 7.5 (2)°], but the phenyl substituent forms a dihedral angle of 56.6 (1)° with the pyridyl ring. The compound crystallizes in the non‐centrosymmetric space group Cc and is a likely candidate for the display of quadratic non‐linear optical effects.     

Two polymorphs of N‐(2‐methoxyphenyl)‐4‐oxo‐4H‐chromone‐3‐carboxamide

The title compound, C₁₇H₁₃NO₄, crystallizes in two polymorphic forms, each with two molecules in the asymmetric unit and in the monoclinic space group P2₁/c. All of the molecules have intramolecular hydrogen bonds involving the amide group. The amide N atoms act as donors to the carbonyl group of the pyrone and also to the methoxy group of the benzene ring. The carbonyl O atom of the amide group acts as an acceptor of the β and β′ C atoms belonging to the aromatic rings. These intramolecular hydrogen bonds have a profound effect on the molecular conformation. In one polymorph, the molecules in the asymmetric unit are linked to form dimers by weak C—H...O interactions. In the other, the molecules in the asymmetric unit are linked by a single weak C—H...O hydrogen bond. Two of these units are linked to form centrosymmetric tetramers by a second weak C—H...O interaction. Further interactions of this type link the molecules into chains, so forming a three‐dimensional network. These interactions in both polymorphs are supplemented by π–π interactions between the chromone rings and between the chromone and methoxyphenyl rings.     

Two three‐dimensional networks in two polymorphs of biphenyl‐4,4′‐diaminium bis(3‐carboxy‐4‐hydroxybenzenesulfonate) dihydrate

Two polymorphs of biphenyl‐4,4′‐diaminium bis(3‐carboxy‐4‐hydroxybenzenesulfonate) dihydrate, C₁₂H₁₄N₂²⁺·2C₇H₅O₆S⁻·2H₂O, have been obtained and crystallographically characterized. Polymorph (I) crystallizes in the space group P2₁/c with Z′ = 2 and polymorph (II) in the space group P with Z′ = 0.5. The benzidinium cation in (II) is located on a crystallographic inversion centre. In both (I) and (II), the sulfonic acid H atoms are transferred to the benzidine N atoms, forming dihydrated 1:2 molecular adducts (base–acid). In the crystal packings of (I) and (II), the component ions are linked into three‐dimensional networks by combinations of X—H...O (X = O, N and C) hydrogen bonds. In addition, π–π interactions are observed in (I) between inversion‐related benzene rings [centroid–centroid distances = 3.632 (2) and 3.627 (2) Å]. In order to simplify the complex three‐dimensional networks in (I) and (II), we also give their rationalized topological analyses.     

Two polymorphs of anhydrous 4‐pyridone at 100 K

Two polymorphs of the title compound, C₅H₅NO, (I), have been obtained from ethanol. One polymorph crystallizes in the monoclinic space group C2/c [henceforth (I)‐M], while the other crystallizes in the orthorhombic space group Pbca [henceforth (I)‐O]. In the two forms, the lattice parameters, cell volume and packing motifs are very similar. There are also two independent molecules of 4‐pyridone in each asymmetric unit. The molecules are linked by N—H...O hydrogen bonds into one‐dimensional zigzag chains extending along the b axis in the (I)‐M polymorph and along the a axis in the (I)‐O polymorph, with the graph set C₂²(12). The structures are stabilized by weak C—H...O hydrogen bonds linking adjacent chains, thus forming a ring with the graph set R₆⁵(28). The significance of this study lies in the analysis of the hydrogen‐bond interactions occurring in these structures. Analyses of the crystal structures of the two polymorphs of 4‐pyridone are helpful in elucidating the mechanism of the generation of spectroscopic effects observed in the IR spectra of these polymorphs in the frequency range of the N—H stretching vibration band.     

cis‐ and trans‐2‐(4‐tert‐Butylcyclohexyloxy)‐1,3,5‐trinitrobenzene

The structures of cis‐ and trans‐2‐(4‐tert‐butyl­cyclo­hexyl­oxy)‐1,3,5‐tri­nitro­benzene, C₁₆H₂₁N₃O₇, (I) and (II), respectively, were determined at low temperature in order to obtain accurate structural parameters for comparison purposes. The C_alkyl—O_ether bond distances are 1.497 (2) and 1.491 (2) Å for (I) and (II), respectively.     

trans‐4‐Bromo‐ONN‐azoxy­benzene at 100 K

The crystal structure of the α isomer of trans‐4‐bromo­azoxy­benzene [systematic name: trans‐1‐(bromophenyl)‐2‐phenyl­diazene 2‐oxide], C₁₂H₉BrN₂O, has been determined by X‐ray dif­frac­tion. The geometries of the two mol­ecules in the asymmetric unit are slightly different and are within ∼0.02 Å for bond lengths, ∼2° for angles and ∼3° for torsion angles. The azoxy bridges in both mol­ecules have the typical geometry observed for trans‐azoxy­benzenes. The crystal network contains two types of planar mol­ecules arranged in columns. The torsion angles along the Ar—N bonds are only 7 (2)°, on either side of the azoxy group.     

The reactivity of human serum albumin toward trans‐4‐hydroxy‐2‐nonenal

Mass spectrometry was used to probe the preferred locations of trans‐4‐hydroxy‐2‐nonenal (HNE) addition to the cysteine, histidine, and lysine residues of human serum albumin (HSA). Considering only those modified peptides supported by high mass accuracy Orbitrap precursor ion measurements (high confidence hits), with HNE:HSA ratios of 1:1 and 10:1, 3 and 15 addition sites, respectively, were identified. Using less stringent criteria, a total of 34 modifications were identified at the higher concentration. To gain quantitative data, iTRAQ labeling studies were completed. Previous work had identified Cys³⁴, the only free cysteine, as the most reactive residue in HSA, and we have found that Lys¹⁹⁹, His^242/7, and His²⁸⁸ are the next most reactive residues. Although the kinetic data indicate that the lysines and histidines can react at relatively similar rates, the results show that lysine addition is much less favorable thermodynamically; under our reaction conditions, lysine addition generally does not go to completion. This suggests that under physiological conditions, HNE addition to lysine is only relevant in situations where unusually high HNE concentrations or access to irreversible secondary reactions are found. Copyright © 2012 John Wiley & Sons, Ltd.     

trans‐4‐Acetylcyclo­hexane­carboxyl­ic acid and ()‐trans‐2‐acetyl­cyclo­hexane­carboxyl­ic acid: hydrogen‐bonding patterns in two isomeric keto acids

Both title compounds, C₉H₁₄O₃, display carboxyl‐dimer hydrogen‐bonding patterns. The 4‐acetyl isomer adopts a chiral conformation with negligible disordering of the methyl and carboxyl groups and forms centrosymmetric dimers across the b and c edges of the chosen cell [O?O = 2.667 (3) Å and O—H?O = 175°]. Intermolecular C—H?O close contacts were found for both carbonyl groups. In the 2‐acetyl isomer, there is no intramolecular interaction between the carboxyl and acetyl groups and the hydrogen bonding involves centrosymmetric carboxyl dimerization across the ab and ac faces of the chosen cell [O?O = 2.668 (2) Å and O—H?O = 173°]. The carboxyl group is negligibly disordered, but significant rotational disordering was found for the acetyl methyl group. An intermolecular C—H?O close contact was found involving the ketone group.     

Photoisomerization of trans‐2‐[4′‐(Dimethylamino)styryl]benzothiazole

Photoreaction of trans‐2‐[4′‐(dimethylamino)styryl]benzothiazole (t‐DMASBT) under direct irradiation has been investigated in dioxane, chloroform, methanol and glycerol to understand the mechanism of photoisomerization. Contrary to an earlier report, isomerization takes place in all these solvents including glycerol. The results show that restriction on photoisomerization leads to the increase in fluorescence quantum yield in glycerol. The results are consistent with the theoretically simulated potential energy surface reported earlier using time‐dependent density functional theory (TDDFT) calculations. DFT calculations on cis isomers under isolated condition have suggested that cis‐B conformer is more stable than cis‐A conformer due to hydrogen‐bonding interaction. In the ground state, cis‐DMASBT is predominantly present as cis‐B. The fluorescence spectra of the irradiated t‐DMASBT suggested that photoisomerization follows not the adiabatic path as proposed by Saha et al., but the nonadiabatic path.     

Polysulfonylamines. CXCI. The `almost' polymorphs rac‐trans‐2‐aminocyclohexan‐1‐aminium di(methanesulfonyl)azanide and its 0.11‐hydrate

The title compound, C₆H₁₅N₂⁺·C₂H₆NO₄S₂⁻, crystallizes as a 0.11‐hydrate, (I), in the space group C2; the asymmetric unit consists of two cations (one of each enantiomer), one anion on a general position, two half anions, each with the N atom on a twofold axis, and approximately one fifth of a water molecule. The general anion departs significantly from the usual conformation: it lacks one of the typical `W'‐shaped sequence of O—S—N—S—O atoms. The compound also crystallizes in the solvent‐free form, (II), in the space group P2₁/c, with one formula unit in the asymmetric unit. Both compounds form ribbons of hydrogen‐bonded cation dimers parallel to the b axis. In (I), there are two independent ribbons of opposite chirality, each involving one anion on a special position, and these ribbons are connected by hydrogen bonds to the anion on a general position, resulting in a layer structure parallel to (100). In (II), the chains are connected by hydrogen bonds, and again a layer structure parallel to (100) results.     

Rate constants of the gas‐phase reactions of OH radicals with trans‐2‐hexenal,trans‐2‐octenal,and trans‐2‐nonenal

The rate constants of the gas‐phase reaction of OH radicals with trans‐2‐hexenal, trans‐2‐octenal, and trans‐2‐nonenal were determined at 298 ± 2 K and atmospheric pressure using the relative rate technique. Two reference compounds were selected for each rate constant determination. The relative rates of OH + trans‐2‐hexenal versus OH + 2‐methyl‐2‐butene and β‐pinene were 0.452 ± 0.054 and 0.530 ± 0.036, respectively. These results yielded an average rate constant for OH + trans‐2‐hexenal of (39.3 ± 1.7) × 10^?12 cm³ molecule^?1 s^?1. The relative rates of OH+trans‐2‐octenal versus the OH reaction with butanal and β‐pinene were 1.65 ± 0.08 and 0.527 ± 0.032, yielding an average rate constant for OH + trans‐2‐octenal of (40.5 ± 2.5) × 10^?12 cm³ molecule^?1 s^?1. The relative rates of OH+trans‐2‐nonenal versus OH+ butanal and OH + trans‐2‐hexenal were 1.77 ± 0.08 and 1.09 ± 0.06, resulting in an average rate constant for OH + trans‐2‐nonenal of (43.5 ± 3.0) × 10^?12 cm³ molecule^?1 s^?1. In all cases, the errors represent 2σ (95% confidential level) and the calculated rate constants do not include the error associated with the rate constant of the OH reaction with the reference compounds. The rate constants for the hydroxyl radical reactions of a series of trans‐2‐aldehydes were compared with the values estimated using the structure activity relationship. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 483–489, 2009     

Two new polymorphs of 2,6‐diaminopyrimidin‐4(3H)‐one monohydrate

The title compound, C₄H₆N₄O·H₂O, crystallized simultaneously as a triclinic and a monoclinic polymorph from an aqueous solution of 2,4‐diaminopyrimidin‐6‐ol. Previously, an orthorhombic polymorph was isolated under the same experimental conditions. The molecular geometric parameters in the two present polymorphs and the previously reported orthorhombic polymorph are similar, but the structures differ in the details of their crystal packing. In the triclinic system, the diaminopyrimidinone molecules are connected to one another via N—H...O and N—H...N hydrogen bonding to form infinite chains in the [011] direction. The chains are further hydrogen bonded to the water molecules, resulting in a three‐dimensional network. In the monoclinic system, the diaminopyrimidinone molecules are hydrogen bonded together into two‐dimensional networks parallel to the bc plane. The water molecules link the planes to form a three‐dimensional polymeric structure.     

Differently coloured polymorphs of 4‐[(2‐nitrophenyl)azo]phenol

The crystal structures of the brown–yellow and orange polymorphs of the title compound, 4‐[(2‐nitro­phenyl)­diazenyl]­phenol, C₁₂H₉N₃O₃, have been determined and their visible reflection spectra recorded. Both structures adopt a stacking arrangement with interstack hydrogen bonds. Ab initio and semi‐empirical (AM1 and INDO‐CISD) calculations were performed in order to rationalize the difference in colour. It can be attributed neither to the subtle distinctions in molecular geometry nor to the effect of intermolecular electrostatic interactions. The most probable origin of this difference is the mixing of intramolecular n π* and intermolecular charge‐transfer excitations.     

1,3‐Propane­di­ammonium bis(3′‐nitro‐trans‐cinnamate) and trans‐1,2‐cyclo­hexane­di­ammonium bis(3′‐nitro‐trans‐cinnamate)

In the title two adducts, C₃H₁₂N₂²⁺·2C₉H₆NO₄^?, (I), and C₆H₁₆N₂²⁺·2C₉H₆NO₄^?, (II), hydrogen bonds between the di­ammonium and carboxyl­ate ions form a two‐dimensional network parallel to the ab plane in (I) and one‐dimensional chains along the c axis in (II). The cyclo­hexane­di­ammonium ion in (II) has a crystallographic twofold axis.     

Conformational polymorphs of 22‐cyano‐N‐methyl‐5‐phenylpent‐2‐en‐4‐ynamide

Although the two polymorphic modifications, (I) and (II), of the title compound, C₁₃H₁₀N₂O, crystallize in the same space group (P2₁/c), their asymmetric units have Z′ values of 1 and 2, respectively. These are conformational polymorphs, since the mol­ecules in phases (I) and (II) adopt different rotations of the phenyl ring with respect the central 2‐cyano­carboxy­amino­prop‐2‐enyl fragment. Calculations of crystal packing using Cerius² [Molecular Simulations (1999). 9685 Scranton Road, San Diego, CA 92121, USA] have shown that (I) is more stable than (II), by 1.3 kcal mol^?1 for the crystallographically determined structures and by 1.56 kcal mol^?1 for the optimized structures (1 kcal mol^?1 = 4.184 kJ mol^?1). This difference is mainly attributed to the different strengths of the hydrogen bonding in the two forms.     

catena‐Poly[[[diaqua­[trans‐3‐(4‐pyri­dyl)acrylato]samarium(III)]‐di‐μ‐trans‐3‐(4‐pyrid­yl)acrylato] dihydrate]

In the title compound, {[Sm(4‐pya)₃(H₂O)₂]·2H₂O}_n [4‐pya is trans‐3‐(4‐pyrid­yl)acrylate, C₈H₆NO₂], each Sm^III atom is ten‐coordinated and has a bicapped square‐antiprismatic coordination geometry. There is a crystallographic center of symmetry at the mid‐point of the Sm⋯Sm line within each [Sm(4‐pya)₃(H₂O)₂]₂ dimer. Each dimer is inter­connected by two pairs of bridging 4‐pya ligands to form a one‐dimensional chain. Neighboring chains are connected via hydrogen bonds to form a three‐dimensional network.     

Two polymorphs of 1,8‐dichloroanthracene

A second, monoclinic, polymorph of the title compound, C₁₄H₈Cl₂, has been found. In addition to the structure of this monoclinic form, the structure of the previously described orthorhombic form [Desvergne, Chekpo & Bouas‐Laurent (1978). J. Chem. Soc. Perkin Trans. 2, pp. 84–87; Benites, Maverick & Fronczek (1996). Acta Cryst. C 52 , 647–648] has been redetermined at low temperature and using modern methods. The low‐temperature structure of the orthorhombic form is of significantly higher quality than the previously published structure and additional details can be derived. A comparison of the crystal packing of the two forms with a focus on weak intermolecular C—H...Cl interactions shows the monoclinic structure to have one such interaction linking the molecules into infinite ribbons, while two crystallographically independent C—H...Cl interactions give rise to an interesting infinite three‐dimensional network in the orthorhombic crystal form.