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.     

4‐(4‐Chloro­benzyl­ideneamino)‐1,5‐dimethyl‐2‐phenyl‐1H‐pyrazol‐3(2H)‐one and 4‐(2‐chloro­benzyl­idene­amino)‐1,5‐dimethyl‐2‐phenyl‐1H‐pyrazol‐3(2H)‐one

The two title compounds, both with formula C₁₈H₁₆ClN₃O, are structurally similar Schiff bases derived from the condensation of 4‐chloro­benzaldehyde or 2‐chloro­benzaldehyde with 4‐amino­anti­pyrine in methanol solution. As expected, both compounds adopt trans configurations about the central C=N bonds. In the crystal structure of the 4‐chloro analogue, mol­ecules are linked through weak C—H⋯O hydrogen bonds, forming chains running along the a axis. In the crystal structure of the 2‐chloro analogue, mol­ecules are linked through weak C—H⋯O and C—H⋯Cl hydrogen bonds, forming layers parallel to the ab plane.     

Green chemistry synthesis: 2‐amino‐3‐[(E)‐(2‐pyridyl)methylideneamino]but‐2‐enedinitrile monohydrate and 5‐cyano‐2‐(2‐pyridyl)‐1‐(2‐pyridylmethyl)‐1H‐imidazole‐4‐carboxamide

The title compounds, C₁₀H₉N₅O·H₂O (L1·H₂O) and C₁₆H₁₂N₆O (L2), were synthesized by solvent‐free aldol condensation at room temperature. L1, prepared by grinding picolinaldehyde with 2,3‐diamino‐3‐isocyanoacrylonitrile in a 1:1 molar ratio, crystallized as a monohydrate. L2 was prepared by grinding picolinaldehyde with 2,3‐diamino‐3‐isocyanoacrylonitrile in a 2:1 molar ratio. By varying the conditions of crystallization it was possible to obtain two polymorphs, viz. L2‐I and L2‐II; both crystallized in the monoclinic space group P2₁/c. They differ in the orientation of one pyridine ring with respect to the plane of the imidazole ring. In L2‐I, this ring is oriented towards and above the imidazole ring, while in L2‐II it is rotated away from and below the imidazole ring. In all three molecules, there is a short intramolecular N—H...N contact inherent to the planarity of the systems. In L1·H₂O, this involves an amino H atom and the C=N N atom, while in L2 it involves an amino H atom and an imidazole N atom. In the crystal structure of L1·H₂O, there are N—H...O and O—H...O intermolecular hydrogen bonds which link the molecules to form two‐dimensional networks which stack along [001]. These networks are further linked via intermolecular N—H...N(cyano) hydrogen bonds to form an extended three‐dimensional network. In the crystal structure of L2‐I, symmetry‐related molecules are linked via N—H...N hydrogen bonds, leading to the formation of dimers centred about inversion centres. These dimers are further linked via N—H...O hydrogen bonds involving the amide group, also centred about inversion centres, to form a one‐dimensional arrangement propagating in [100]. In the crystal structure of L2‐II, the presence of intermolecular N—H...O hydrogen bonds involving the amide group results in the formation of dimers centred about inversion centres. These are linked via N—H...N hydrogen bonds involving the second amide H atom and the cyano N atom, to form two‐dimensional networks in the bc plane. In L2‐I and L2‐II, C—H...π and π–π interactions are also present.     

The first structurally analysed nucleic acid building block containing the Reese protecting group: 2′‐O‐[1‐(2‐fluorophenyl)‐4‐methoxypiperidin‐4‐yl]‐β‐D‐(1′R,2′R,3′R,4′R)‐uridine

The title compound, C₂₁H₂₆FN₃O₇, is assembled by N—H...O and O—H...O hydrogen bonds into well‐separated two‐dimensional layers of about 15 Å thickness. The crescent conformation of the molecules is stabilized by weak intramolecular C—H...O and C—H...F hydrogen bonds. The uridine moiety adopts an anti conformation. The ribofuranose ring exists in an envelope conformation. All the endocyclic uracil bonds are shorter than normal single C—N and C—C bonds, and five of them have comparable lengths, which implies a considerable degree of delocalization of the electron density within this ring.     

(2S)‐1‐Carbamoylpyrrolidine‐2‐carboxylic acid

In the title compound, also known as N‐carbamoyl‐l ‐proline, C₆H₁₀N₂O₃, the pyrrolidine ring adopts a half‐chair conformation, whereas the carboxyl group and the mean plane of the ureide group form an angle of 80.1 (2)°. Molecules are joined by N—H...O and O—H...O hydrogen bonds into cyclic structures with graph‐set R²₂(8), forming chains in the b‐axis direction that are further connected via N—H...O hydrogen bonds into a three‐dimensional network.     

2‐Amino‐5‐methyl­pyridinium (2‐amino‐5‐methyl­pyridine)trichloro­zincate(II)

The title compound, (C₆H₉N₂)[ZnCl₃(C₆H₈N₂)], consists of one 2‐amino‐5‐methyl­pyridinium cation and one (2‐amino‐5‐methyl­pyridine)trichloro­zincate(II) anion, which are held together by N—H·Cl hydrogen bonds and π–π inter­actions. The cation and the pyridine ligand show similar geometric features, except for the N—C bond lengths. Mol­ecules of the title compound are connected by N—H·Cl hydrogen bonds to form chiral chains; these chains are associated further by C—H·Cl hydrogen bonds to form layers, which are in turn linked by π–π inter­actions.     

2‐[2‐(Pyrrolidin‐2‐yl)propan‐2‐yl]‐1H‐pyrrole and its amide derivative 1‐{2‐[2‐(1H‐pyrrol‐2‐yl)propan‐2‐yl]pyrrolidin‐1‐yl}ethanone

In the title compounds, C₁₁H₁₈N₂, (II), and C₁₃H₂₀N₂O, (III), the pyrrolidine rings have twist conformations. Compound (II) crystallizes with two independent molecules (A and B) in the asymmetric unit. The mean planes of the pyrrole and pyrrolidine rings are inclined to one another by 89.99 (11) and 89.35 (10)° in molecules A and B, respectively. In (III), the amide derivative of (II), the same dihedral angle is much smaller, at only 13.42 (10)°. In the crystal structure of (II), the individual molecules are linked via N—H...N hydrogen bonds to form inversion dimers, each with an R²₂(12) graph‐set motif. In the crystal structure of (III), the molecules are linked via N—H...O hydrogen bonds to form inversion dimers with an R²₂(16) graph‐set motif.     

(E)‐4‐[(2‐Carbamoylhydrazinylidene)methyl]‐3‐hydroxy‐5‐hydroxymethyl‐2‐methylpyridin‐1‐ium nitrate

The title compound, C₉H₁₃N₄O₃⁺·NO₃⁻, is the first structurally characterized Schiff base derived from semicarbazide and pyridoxal. Unusually for an unsubstituted semicarbazone, the compound adopts a syn conformation, in which the carbonyl O atom is in a cis disposition relative to the azomethine N atom. This arrangement is supported by a pair of hydrogen bonds between the organic cation and the nitrate anion. The cation is essentially planar, with only a hydroxymethyl O atom deviating significantly from the mean plane of the remaining atoms (r.m.s. deviation of the remaining non‐H atoms = 0.01 Å). The molecules are linked into flat layers by N—H...O and C—H...O hydrogen bonds. O—H...O hydrogen bonds involving the hydroxymethyl group as a donor interconnect the layers into a three‐dimensional structure.     

2‐Ethyl‐6‐methylpyridin‐3‐ol and its salt bis(2‐ethyl‐3‐hydroxy‐6‐methylpyridinium) succinate

The title compounds, C₈H₁₁NO, (I), and 2C₈H₁₂NO⁺·C₄H₄O₄²⁻, (II), both crystallize in the monoclinic space group P2₁/c. In the crystal structure of (I), intermolecular O—H...N hydrogen bonds combine the molecules into polymeric chains extending along the c axis. The chains are linked by C—H...π interactions between the methylene H atoms and the pyridine rings into polymeric layers parallel to the ac plane. In the crystal structure of (II), the succinate anion lies on an inversion centre. Its carboxylate groups interact with the 2‐ethyl‐3‐hydroxy‐6‐methylpyridinium cations via intermolecular N—H...O hydrogen bonds with the pyridine ring H atoms and O—H...O hydrogen bonds with the hydroxy H atoms to form polymeric chains, which extend along the [01] direction and comprise R₄⁴(18) hydrogen‐bonded ring motifs. These chains are linked to form a three‐dimensional network through nonclassical C—H...O hydrogen bonds between the pyridine ring H atoms and the hydroxy‐group O atoms of neighbouring cations. π–π interactions between the pyridine rings and C—H...π interactions between the methylene H atoms of the succinate anion and the pyridine rings are also present in this network.     

Piperidinium 3‐[(4‐hydroxy‐5,7‐di­methyl‐2‐oxo‐2H‐chromen‐3‐yl)­phenyl­methyl]‐5,7‐di­methyl‐2‐oxo‐2H‐chromen‐4‐olate

In the title salt, C₅H₁₂N⁺·C₂₉H₂₃O₆^?, both benzo­pyran systems are planar. Intermolecular N—H?O hydrogen bonds and a short O—H?O intramolecular hydrogen bond are observed in the structure.     

2‐(4‐Hydroxy­phenyl)‐4,4‐dimethyl‐2‐oxazoline: X‐ray and density functional theory study

In the crystal structure of the title compound, C₁₁H₁₃NO₂, there are strong inter­molecular O—H⋯N hydrogen bonds which, together with weak intra­molecular C—H⋯O hydrogen bonds, lead to the formation of infinite chains of mol­ecules, held together by weak inter­molecular C—H⋯O hydrogen bonds. A theoretical investigation of the hydrogen bonding, based on density functional theory (DFT) employing periodic boundary conditions, is in agreement with the experimental data. The cluster approach shows that the influence of the crystal field and of hydrogen‐bond formation are responsible for the deformation of the 2‐oxazoline ring, which is not planar and adopts a ⁴T₃ (^C3T_C2) conformation.     

(R)‐N‐[(R)‐1‐(2‐Hydroxy‐5‐methyl­phenyl)‐2‐phenyl­ethyl]‐2‐methyl‐1‐phenyl­propyl­ammonium chloride

In the title compound, C₂₅H₃₀NO⁺·Cl⁻, the mol­ecules are linked by a combination of inter­molecular N—H⋯Cl and O—H⋯Cl hydrogen bonds and intra­molecular N—H⋯O hydrogen bonds. The absolute configuration of the new stereogenic centre (the C atom adjacent to the N atom on the phenol side) is determined to have an R configuration.     

4‐Phenyl­butan‐2‐one semi­carbazone

The title compound, C₁₁H₁₅N₃O, crystallizes with two mol­ecules in the asymmetric unit, which are held together by an extended network of hydrogen bonds. It is remarkable that only five of the six theoretically possible hydrogen bonds are formed.     

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.     

16‐(4‐Cyanobenzylidene)‐3β‐pyrrolidinoandrost‐5‐en‐17β‐ol monohydrate

In the title compound, C₃₁H₄₀N₂O·H₂O, the outer two six‐membered rings are in chair conformations, while the central ring is in an 8β,9α‐half‐chair conformation. The five‐membered ring adopts a 13β‐envelope conformation and the cyano­benzyl­idene moiety has an E configuration with respect to the hydroxyl group at position 17. The steroid nuclei are linked by intermolecular O—H?O and O—H?N hydrogen bonds to form a molecular network. The molecular packing has an interesting feature, with the steroids aligned parallel to the b axis, forming a closed loop through hydrogen bonds linked via water mol­ecules.     

4‐[(2‐Hydroxyethyl)iminomethyl]‐5‐hydroxymethyl‐2‐methylpyridin‐3‐ol

The title compound, C₁₀H₁₄N₂O₃, is a Schiff base which is derived from pyridoxal and represents, therefore, a vitamin B₆‐related compound. Molecules are linked into sheets by a combination of O—H...O and O—H...N hydrogen bonds.     

Similarities and differences in the structures of 5‐bromo‐6‐hydroxy‐7,8‐dimethylchroman‐2‐one and 6‐hydroxy‐7,8‐dimethyl‐5‐nitrochroman‐2‐one

The title compounds, C₁₁H₁₁BrO₃, (I), and C₁₁H₁₁NO₅, (II), respectively, are derivatives of 6‐hydroxy‐5,7,8‐trimethylchroman‐2‐one substituted at the 5‐position by a Br atom in (I) and by a nitro group in (II). The pyranone rings in both molecules adopt half‐chair conformations, and intramolecular O—H...Br [in (I)] and O—H...O_nitro [in (II)] hydrogen bonds affect the dispositions of the hydroxy groups. Classical intermolecular O—H...O hydrogen bonds are found in both molecules but play quite dissimilar roles in the crystal structures. In (I), O—H...O hydrogen bonds form zigzag C(9) chains of molecules along the a axis. Because of the tetragonal symmetry, similar chains also form along b. In (II), however, similar contacts involving an O atom of the nitro group form inversion dimers and generate R₂²(12) rings. These also result in a close intermolecular O...O contact of 2.686 (4) Å. For (I), four additional C—H...O hydrogen bonds combine with π–π stacking interactions between the benzene rings to build an extensive three‐dimensional network with molecules stacked along the c axis. The packing in (II) is much simpler and centres on the inversion dimers formed through O—H...O contacts. These dimers are stacked through additional C—H...O hydrogen bonds, and further weak C—H...O interactions generate a three‐dimensional network of dimer stacks.     

1‐(1‐Amino‐4‐bromo‐9,10‐dioxo‐9,10‐dihydro­anthracen‐2‐ylcarbon­yl)‐1,3‐dicyclo­hexyl­urea

In the title compound, C₂₈H₃₀BrN₃O₄, the mol­ecules are linked by C—H⋯Br and N—H⋯O hydrogen bonds into one‐dimensional chains, which are arranged into a three‐dimensional network through a combination of C—H⋯O hydrogen bonds and two kinds of π–π inter­actions between the benzene rings of the anthraquinone units.     

Bis[μ‐1‐(1,10‐phenanthrolin‐2‐yl)‐2‐pyridone]bis{aqua[1‐(1,10‐phenanthrolin‐2‐yl)‐2‐pyridone]cadmium(II)} tetrakis(perchlorate)

In the title centrosymmetric binuclear complex, [Cd₂(C₁₇H₁₁N₃O)₄(H₂O)₂](ClO₄)₄, the Cd^II ion assumes a distorted octahedral geometry. There are π–π stacking interactions between the pyridine and 1,10‐phenanthroline ring systems of adjacent ligands at the same Cd^II centre. Intermolecular hydrogen bonds between the coordinated aqua ligand and the O atom of a keto group connect adjacent complex cations into extended chains. Hydrogen bonds also exist between the complex cations and the perchlorate anions. Compared with the fluorescence spectrum of the organic ligand, the complex displays strong fluorescent emission and an ipsochromic shift of the emission peaks, which may be attributed to the structural character.     

N‐(X‐Chlorophenyl)‐4‐hydroxy‐2‐methyl‐2H‐1,2‐benzothiazine‐3‐carboxamide 1,1‐dioxide (with X = 2 and 4)

The structures of N‐(2‐chlorophenyl)‐4‐hydroxy‐2‐methyl‐2H‐1,2‐benzothiazine‐3‐carboxamide 1,1‐dioxide and N‐(4‐chlorophenyl)‐4‐hydroxy‐2‐methyl‐2H‐1,2‐benzothiazine‐3‐carboxamide 1,1‐dioxide, both C₁₆H₁₃ClN₂O₄S, are stabilized by extensive intramolecular hydrogen bonds. The 4‐chloro derivative forms dimeric pairs of molecules lying about inversion centres as a result of intermolecular N—H...O hydrogen bonds, forming 14‐membered rings representing an R₂²(14) motif; the 2‐chloro derivative is devoid of any such intermolecular hydrogen bonds. The heterocyclic thiazine rings in both structures adopt half‐chair conformations.