2‐(2‐Oxazolin‐2‐yl)benzene‐1,4‐diol: X‐ray and density functional theory studies

In the crystal structure of the title compound, C₉H₉NO₃, there are strong intra­molecular O—H⋯N and inter­molecular O—H⋯O hydrogen bonds which, together with weak inter­molecular C—H⋯O hydrogen bonds, lead to the formation of infinite chains of mol­ecules. The calculated inter­molecular hydrogen‐bond energies are −11.3 and −2.7 kJ mol⁻¹, respectively, showing the dominant role of the O—H⋯O hydrogen bonding. A natural bond orbital analysis revealed the electron contribution of the lone pairs of the oxazoline N and O atoms, and of the two hydr­oxy O atoms, to the order of the relevant bonds.     

3‐(4‐Bromophenyl)‐5‐(4‐dimethylaminophenyl)‐1‐phenyl‐2‐pyrazoline: X‐ray and density functional theory (DFT) studies

In the crystal structure of the title compound, C₂₃H₂₂BrN₃, a strong conjugation of the pyrazoline chromophore with the aromatic rings at positions 1 and 3 is observed, as well as a significant shift in the synclinal→synperiplanar direction. The absolute structure was unequivocally determined. In the absence of clasical hydrogen‐bond donors, the structure is stabilized by weak C—H...π interactions. This paper also reports the electronic structure of the title compound using NBO (natural bond order) analysis. The contributions of lone pairs to the relevant bonds were revealed.     

Ethyl 3‐[1‐(5,5‐dimethyl‐2‐oxo‐1,3,2‐dioxaphosphorin‐2‐yl)propan‐2‐ylidene]carbazate: a combined X‐ray and density functional theory (DFT) study

In the title compound, C₁₁H₂₁N₂O₅P, one of the two carbazate N atoms is involved in the C=N double bond and the H atom of the second N atom is engaged in an intramolecular hydrogen bond with an O atom from the dimethylphosphorin‐2‐yl group, which is in an uncommon cis position with respect to the carbamate group. The cohesion of the crystal structure is also reinforced by weak intermolecular hydrogen bonds. Density functional theory (DFT) calculations at the B3LYP/6‐311++g(2d,2p) level revealed the lowest energy structure to have a Z configuration at the C=N bond, which is consistent with the configuration found in the X‐ray crystal structure, as well as a less stable E counterpart which lies 2.0 kcal mol⁻¹ higher in potential energy. Correlations between the experimental and computational studies are discussed.     

2‐Anilinomethyl­ene‐3‐oxobutane­nitrile: an X‐ray and density functional theory study

Mol­ecules of the title compound, C₁₁H₁₀N₂O, are effectively planar. In the crystal structure, they are stabilized primarily by electrostatic inter­actions, as the dipole moment of the mol­ecule is 4.56 D. In addition, the mol­ecules are linked by weak C—H⋯N and C—H⋯O hydrogen bonds. An analysis of bonding conditions in the mol­ecule was carried out using natural bond orbital (NBO) formalism.     

Three isomeric forms of hydroxyphenyl‐2‐oxazoline: 2‐(2‐hydroxyphenyl)‐2‐oxazoline, 2‐(3‐hydroxyphenyl)‐2‐oxazoline and 2‐(4‐hydroxyphenyl)‐2‐oxazoline

Crystal structures are reported for three isomeric compounds, namely 2‐(2‐hydroxy­phenyl)‐2‐oxazoline, (I), 2‐(3‐hydroxy­phenyl)‐2‐oxazoline, (II), and 2‐(4‐hydroxy­phenyl)‐2‐oxazoline, (III), all C₉H₉NO₂ [systematic names: 2‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (I), 3‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (II), and 4‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (III)]. In these compounds, the deviation from coplanarity of the oxazoline and benzene rings is dependent on the position of the hydroxy group on the benzene ring. The coplanar arrangement in (I) is stabilized by a strong intra­molecular O—H⋯N hydrogen bond. Surprisingly, the 2‐oxazoline ring in mol­ecule B of (II) adopts a ³T₄ (^C2T_C3) conformation, while the 2‐oxazoline ring in mol­ecule A, as well as that in (I) and (III), is nearly planar, as expected. Tetra­mers of mol­ecules of (II) are formed and they are bound together via weak C—H⋯N hydrogen bonds. In (III), strong inter­molecular O—H⋯N hydrogen bonds and weak intra­molecular C—H⋯O hydrogen bonds lead to the formation of an infinite chain of mol­ecules perpendicular to the b direction. This paper also reports a theoretical investigation of hydrogen bonds, based on density functional theory (DFT) employing periodic boundary conditions.     

(E)‐Methyl 2‐anilinomethylene‐3‐oxobutanoate: X‐ray and density functional theory studies

Molecules of the title compound, C₁₂H₁₃NO₃, are not planar and are stabilized by electrostatic interactions, as the dipole moment of the molecule is 3.76 D. They are also stabilized by intramolecular hydrogen bonds of N...O and C...O types, and by a complicated network of weak intermolecular hydrogen bonds of the C...O type. This paper also reports the theoretical investigation of the hydrogen bonding and electronic structure of the title compound using natural bond orbital (NBO) analysis.     

(E)‐Methyl 2‐[(2‐fluorophenyl)aminomethylene]‐3‐oxobutanoate: X‐ray and density functional theory (DFT) study

The title compound, C₁₂H₁₂FNO₃, a potential precursor for fluoroquinoline synthesis, is essentially planar, with the most outlying atoms displaced from the best‐plane fit through all non‐H atoms by 0.163 (2) and 0.118 (2) Å. Molecules are arranged in layers oriented parallel to the (011) plane. The arrangement of the molecules in the structure is controlled mainly by electrostatic interactions, as the dipole moment of the molecule is 5.2 D. In addition, the molecules are linked by a weak C—H...O hydrogen bond which gives rise to chains with the base vector [1,1,1]. Electron transfer within the molecule is analysed using natural bond orbital (NBO) analysis. Deviations from the ideal molecular geometry are explained by the concept of non‐equivalent hybrid orbitals.     

N‐Methyl‐N‐phenylaminomethyl 2‐naphthyl ketone: an X‐ray diffraction and density functional theory study

The crystallographically observed molecular structure of the title compound, C₁₉H₁₇NO, and its inverted counterpart are compared with that calculated by density functional theory (DFT) at the B3LYP/6‐311++G(d,p) level. The results from both methods suggest that the observed molecular conformation of the title compound is primarily determined by intermolecular interactions in the crystal structure. The periodic organization of the molecules is stabilized by weak C—H...O and C—H...π hydrogen bonds and thus a two‐dimensional puckered network consisting of R₄⁴(22) and R₄⁴(38) ring motifs is established. The title molecule has a (+)‐antiperiplanar conformation about the C—C bond in the aminoacetone bridge. The pyramidal geometry observed around the vertex N atom is flattened by the presence of bulky phenyl and naphthylethanone fragments.     

anti‐2‐Hydr­oxy‐2‐methyl‐1‐tetra­lone oxime: X‐ray and density functional theory study

Crystals of the title racemic compound, C₁₁H₁₃NO₂, consist of two types of mol­ecules (conformers); one mol­ecule has an exocyclic OH group in an equatorial position and the other has this group in an axial position. Consequently, the hydrogen‐bond schemes for the two mol­ecules are different. The mol­ecules with equatorial OH groups create infinite parallel chains (formed by the same enantio­mer), connected by centrosymmetric dimers of mol­ecules (of mixed enantio­mers), both with axial OH groups. Possible inter­conversion of the conformers and the flexibility of the mol­ecule were studied by means of different MP2 and density functional theory (DFT) methods. The optimization of the structure by the DFT method confirmed the types of the hydrogen bonds.     

3‐(4‐Acetyl­phenyl)‐1‐(4‐nitro­phenyl)­triazene

The crystal structure of the title compound, C₁₄H₁₂N₄O₃, shows that the stereochemistry about the N=N double bond of the N=N—N(H) moiety is trans. The whole mol­ecule is almost planar (r.m.s. deviation = 0.0654 Å), the interplanar angle between the phenyl rings being 0.7 (1)° and the largest interplanar angle being that between the phenyl ring and the nitro group of the 4‐nitro­phenyl substituent [11.5 (2)°]. Intermolecular N—H⋯O interactions between mol­ecules related by translation give rise to chains along the [110] and [10] directions, and these chains are held together by N⋯O π–π interactions. An unequal distribution of the double‐bond character among the N atoms suggests a delocalization of π electrons over the diazo­amine group and the adjacent aryl substituents.     

An X‐ray crystallographic and density functional theory study of (3Z)‐4‐(5‐ethylsulfonyl‐2‐hydroxyanilino)pent‐3‐en‐2‐one and (3Z)‐4‐(5‐tert‐butyl‐2‐hydroxyanilino)pent‐3‐en‐2‐one

The Schiff base enaminones (3Z)‐4‐(5‐ethylsulfonyl‐2‐hydroxyanilino)pent‐3‐en‐2‐one, C₁₃H₁₇NO₄S, (I), and (3Z)‐4‐(5‐tert‐butyl‐2‐hydroxyanilino)pent‐3‐en‐2‐one, C₁₅H₂₁NO₂, (II), were studied by X‐ray crystallography and density functional theory (DFT). Although the keto tautomer of these compounds is dominant, the O=C—C=C—N bond lengths are consistent with some electron delocalization and partial enol character. Both (I) and (II) are nonplanar, with the amino–phenol group canted relative to the rest of the molecule; the twist about the N(enamine)—C(aryl) bond leads to dihedral angles of 40.5 (2) and −116.7 (1)° for (I) and (II), respectively. Compound (I) has a bifurcated intramolecular hydrogen bond between the N—H group and the flanking carbonyl and hydroxy O atoms, as well as an intermolecular hydrogen bond, leading to an infinite one‐dimensional hydrogen‐bonded chain. Compound (II) has one intramolecular hydrogen bond and one intermolecular C=O...H—O hydrogen bond, and consequently also forms a one‐dimensional hydrogen‐bonded chain. The DFT‐calculated structures [in vacuo, B3LYP/6‐311G(d,p) level] for the keto tautomers compare favourably with the X‐ray crystal structures of (I) and (II), confirming the dominance of the keto tautomer. The simulations indicate that the keto tautomers are 20.55 and 18.86 kJ mol⁻¹ lower in energy than the enol tautomers for (I) and (II), respectively.     

4‐(3,5‐Dimethyl‐1H‐pyrazol‐4‐ylmethyl)‐3,5‐dimethyl‐1H‐pyrazol‐2‐ium dihydrogen phosphate: a combined X‐ray and DFT study

The molecular structure of the title salt, C₁₁H₁₇N₄⁺·H₂PO₄⁻, has been determined from single‐crystal X‐ray analysis and compared with the structure calculated by density functional theory (DFT) at the BLYP level. The crystal packing in the title compound is stabilized primarily by intermolecular N—H...O, O—H...N and O—H...O hydrogen bonds and π–π stacking interactions, and thus a three‐dimensional supramolecular honeycomb network consisting of R₄²(10), R₄⁴(14) and R₄⁴(24) ring motifs is established. The HOMO–LUMO energy gap (1.338 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital) indicates a high chemical reactivity for the title compound.     

A linear solvation energy relationship study for the reactivity of 2‐(4‐substituted phenyl)‐cyclohex‐1‐enecarboxylic, 2‐(4‐substituted phenyl)‐benzoic,and 2‐(4‐substituted phenyl)‐acrylic acids with diazodiphenylmethane in various solvents

The reactivities of 2‐(4‐substituted phenyl)‐cyclohex‐1‐enecarboxylic acids, 2‐(4‐substituted phenyl)‐benzoic acids, and 2‐(4‐substituted phenyl)‐acrylic acids with diazodiphenylmethane in various solvents were investigated. To explain the kinetic results through solvent effects, the second‐order rate constants of the examined acids were correlated using the Kamlet–Taft solvatochromic equation. The correlations of the kinetic data were carried out by means of multiple linear regression analysis, and the solvent effects on the reaction rates were analyzed in terms of initial and transition state contributions. The signs of the equation coefficients support the proposed reaction mechanism. The solvation models for all investigated carboxylic acids are suggested. The quantitative relationship between the molecular structure and the chemical reactivity is discussed, as well as the effect of geometry on the reactivity of the examined molecules. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 430–439, 2010     

N,N‐Diethyl‐N′‐[(E)‐4‐pyridylmethylene]benzene‐1,4‐diamine: a combined X‐ray and density functional theory study

The crystal structure of the title compound, C₁₆H₁₉N₃, comprises neutral molecules of a dipolar Schiff base chromophore. A density functional theory (DFT) optimized structure at the B3LYP/6‐31G(d) level is compared with the molecular structure in the solid state. The compound crystallizes in the noncentrosymmetric space group Pna2₁ with a herring‐bone packing motif and is therefore a potential candidate for nonlinear optical effects in the bulk.     

(E)‐4‐(4‐Bromo­phenyl­diazen­yl)‐2,6‐dimethyl­phenyl acrylate and (E)‐2,6‐dimethyl‐4‐(4‐methyl­phenyl­diazen­yl)­phenyl acrylate

The crystal structures of the title compounds, C₁₇H₁₅BrN₂O₂, (I), and C₁₈H₁₈N₂O₂, (II), determined at room temperature, have a trans configuration with respect to the diazene linkage, as found for other azo (diazene) derivatives. The aromatic mean planes are nearly coplanar, with a dihedral angle between these planes of 8.31 (2)° for (I) and 3.74 (2)° for (II). In both complexes, the mean plane of the ester group is nearly perpendicular to the aromatic ring planes. In both compounds, the crystal packing involves only π–π and π–ring inter­actions, which combine to stabilize the extended structure.     

1,4‐Bis[2‐(4‐ferrocenylphenyl)ethynyl]anthraquinone from synchrotron X‐ray powder diffraction

The title compound, [Fe₂(C₅H₅)₂(C₄₀H₂₂O₂)] or 1,4‐(FcPh)₂Aq [where FcPh is 2‐(4‐ferrocenylphenyl)ethynyl and Aq is anthraquinone], was synthesized in an attempt to obtain a new solvent‐incorporating porous material with a large void space. Thermodynamic data for 1,4‐(FcPh)₂Aq show a phase transition at approximately 430 K. The crystal structure of solvent‐free 1,4‐(FcPh)₂Aq was determined at temperatures of 90, 300 and 500 K using synchrotron powder diffraction data. A direct‐space method using a genetic algorithm was employed for structure solution. Charge densities calculated from observed structure factors by the maximum entropy method were employed for model improvement. The final models were obtained through multistage Rietveld refinements. In both phases, the structures of which differ only subtly, the planar Aq fragments are stacked alternately in opposite orientations, forming a one‐dimensional column. The FcPh arms lie between the stacks and fill the remaining space, leaving no voids. C—H...π interactions between the Ph and Fc fragments mediate crystal packing and stabilization.     

1‐(4‐Bromo­phenyl)‐3‐(4‐methyl­phenyl)­prop‐2‐en‐1‐one

In the mol­ecule of the title compound, C₁₆H₁₃BrO, the two benzene rings are rotated in opposite directions with respect to the central C—C=C—C part of the mol­ecule. The phenone O atom deviates from the least‐squares plane of the mol­ecule by 0.300 (3) Å. In the crystal structure, mol­ecules are paired through C—H⋯π interactions. The molecular pairs along [001] are hydrogen bonded through three translation‐related co‐operative hydrogen bonds in the `bay area', forming molecular chains, which are further hydrogen bonded through C—H⋯Br weak interactions, forming (010) molecular layers. In the third direction, there are only weak van der Waals interactions. The co‐operative hydrogen bonds in the `bay area' are discussed briefly.     

N‐(4‐Cyano­phenyl)‐α‐(4‐methoxy­phenyl)­nitro­ne

In the crystal structure of the title compound, 4‐cyano‐N‐(4‐methoxy­benzyl­idene)­phenyl­amine N‐oxide, C₁₅H₁₂N₂O₂, the 4‐methoxy­phenyl is approximately coplanar with the nitrone moiety but significantly rotated with respect to the 4‐cyano­phenyl moiety. The extent of this rotation is significantly different for the two crystallographically independent mol­ecules of the asymmetric unit [dihedral angles of 19.4 (1) and 26.5 (1)°]. The geometry about the C=N bond is Z. The two mol­ecules are related to one another by a pseudo inversion centre.     

1‐[2‐(1‐Hydroxy­cyclo­hexyl)‐2‐(4‐methoxy­phenyl)­ethyl]­di­methyl­ammon­ium chloride (venlafaxine hydro­chloride)

The crystal structure of racemic Venlafaxine hydro­chloride, C₁₇H₂₈NO₂⁺·Cl^?, consists of two types of parallel chains formed by translated Venlafaxine⁺ cations, hydrogen bonded by Cl^? anions, and characterized by the opposite chirality of their constituent mol­ecules. These chains organize in two different types of broad layers of opposite handedness, related by a glide plane.     

Ethyl 2‐form­amido‐2‐(4‐iodo­benzyl)‐3‐(4‐iodo­phenyl)­propionate and ethyl 2‐(3‐bromo­benzyl)‐3‐(3‐bromo­phenyl)‐2‐form­amidopropionate

The title compounds, C₁₉H₁₉I₂NO₃ and C₁₉H₁₉Br₂NO₃, are derivatives of α‐amino­isobutyric acid with halogen substituents at the para and meta positions, respectively. The ethoxycarbonyl and formamide side chains attached to the C_α atom of the mol­ecule adopt extended and folded conformations, respectively. The crystal structures are stabilized by N—H⃛O, C—H⃛O, C—Br⃛O and C—I⃛O interactions.