Synthesis and Investigation of 1,3‐Bis(5‐nitraminotetrazol‐1‐yl)propan‐2‐ol and its Salts

1,3‐Bis(5‐nitraminotetrazol‐1‐yl)propan‐2‐ol ( 5 ) was prepared by the reaction of 5‐aminotetrazole and 1,3‐dichloroisopropanol under basic conditions. Obtained 1,3‐bis(5‐aminotetrazol‐1‐yl)propan‐2‐ol ( 3 ) was nitrated with 100 % nitric acid. In this context in situ hydrolysis of the nitrate ester was studied. Metal and nitrogen‐rich salts of the neutral compound 5 were prepared and analyzed. Crystal structures of three salts and the sensitivities toward impact, friction and electrostatic discharge were determined as well. The performance values of the compounds were calculated using the EXPLO5 program. A detailed comparison of the different salts is also enclosed.     

A new polymorph of 1‐ferrocenyl‐3‐(3‐nitroanilino)propan‐1‐one

Recrystallization of the title compound, [Fe(C₅H₅)(C₁₄H₁₃N₂O₃)], from a mixture of n‐hexane and dichloromethane gave the new polymorph, denoted (I), which crystallizes in the same space group (P) as the previously reported structure, denoted (II). The Fe—C distances in (I) range from 2.015 (3) to 2.048 (2) Å and the average value of the C—C bond lengths in the two cyclopentadienyl (Cp) rings is 1.403 (13) Å. As indicated by the smallest C—Cg1—Cg2—C torsion angle of 1.4° (Cg1 and Cg2 are the centroids of the two Cp rings), the orientation of the Cp rings in (I) is more eclipsed than in the case of (II), for which the value was 15.3°. Despite the pronounced conformational similarity between (I) and (II), the formation of self‐complementary N—H...O hydrogen‐bonded dimers represents the only structural motif common to the two polymorphs. In the extended structure, molecules of (I) utilize C—H...O hydrogen bonds and, unlike (II), an extensive set of intermolecular C—H...π interactions. Fingerprint plots based on Hirshfeld surfaces are used to compare the packing of the two polymorphs.     

Cobalt(II) chloride adducts with acetonitrile,propan‐2‐ol and tetrahydrofuran: considerations on nuclearity,reactivity and synthetic applications

High‐spin cobalt(II) complexes are considered useful building blocks for the synthesis of single‐molecule magnets (SMM) because of their intrinsic magnetic anisotropy. In this work, three new cobalt(II) chloride adducts with labile ligands have been synthesized from anhydrous CoCl₂, to be subsequently employed as starting materials for heterobimetallic compounds. The products were characterized by elemental, spectroscopic (EPR and FT–IR) and single‐crystal X‐ray diffraction analyses. trans‐Tetrakis(acetonitrile‐κN )bis(tetrahydrofuran‐κO )cobalt(II) bis[(acetonitrile‐κN )trichloridocobaltate(II)], [Co(C₂H₃N)₄(C₄H₈O)₂][CoCl₃(C₂H₃N)]₂, (1), comprises mononuclear ions and contains both acetonitrile and tetrahydrofuran (thf) ligands, The coordination polymer catena‐poly[[tetrakis(propan‐2‐ol‐κO )cobalt(II)]‐μ‐chlorido‐[dichloridocobalt(II)]‐μ‐chlorido], [Co₂Cl₄(C₃H₈O)₄], (2′), was prepared by direct reaction between anhydrous CoCl₂ and propan‐2‐ol in an attempt to rationalize the formation of the CoCl₂–alcohol adduct (2), probably CoCl₂(HOⁱPr)_m . The binuclear complex di‐μ‐chlorido‐1:2κ⁴Cl :Cl‐dichlorido‐2κ²Cl‐tetrakis(tetrahydrofuran‐1κO )dicobalt(II), [Co₂Cl₄(C₄H₈O)₄], (3), was obtained from (2) after recrystallization from tetrahydrofuran. All three products present cobalt(II) centres in both octahedral and tetrahedral environments, the former usually less distorted than the latter, regardless of the nature of the neutral ligand. Product (2′) is stabilized by an intramolecular hydrogen‐bond network that appears to favour a trans arrangement of the chloride ligands in the octahedral moiety; this differs from the cis disposition found in (3). The expected easy displacement of the bound solvent molecules from the metal coordination sphere makes the three compounds good candidates for suitable starting materials in a number of synthetic applications.     

Hydrogen‐bonded structures of the 1:1 and 1:2 compounds of chloranilic acid with pyrrolidin‐2‐one and piperidin‐2‐one

In the four compounds of chloranilic acid (2,5‐dichloro‐3,6‐dihydroxycyclohexa‐2,5‐diene‐1,4‐dione) with pyrrolidin‐2‐one and piperidin‐2‐one, namely, chloranilic acid–pyrrolidin‐2‐one (1/1), C₆H₂Cl₂O₄·C₄H₇NO, (I), chloranilic acid–pyrrolidin‐2‐one (1/2), C₆H₂Cl₂O₄·2C₄H₇NO, (II), chloranilic acid–piperidin‐2‐one (1/1), C₆H₂Cl₂O₄·C₅H₉NO, (III), and chloranilic acid–piperidin‐2‐one (1/2), C₆H₂Cl₂O₄·2C₅H₉NO, (IV), the shortest interactions between the two components are O—H...O hydrogen bonds, which act as the primary intermolecular interaction in the crystal structures. In (II), (III) and (IV), the chloranilic acid molecules lie about inversion centres. For (III), this necessitates the presence of two independent acid molecules. In (I), there are two formula units in the asymmetric unit. The O...O distances are 2.4728 (11) and 2.4978 (11) Å in (I), 2.5845 (11) Å in (II), 2.6223 (11) and 2.5909 (10) Å in (III), and 2.4484 (10) Å in (IV). In the hydrogen bond of (IV), the H atom is disordered over two positions with site occupancies of 0.44 (3) and 0.56 (3). This indicates that proton transfer between the acid and base has partly taken place to form ion pairs. In (I) and (II), N—H...O hydrogen bonds, the secondary intermolecular interactions, connect the pyrrolidin‐2‐one molecules into a dimer, while in (III) and (IV) these hydrogen bonds link the acid and base to afford three‐ and two‐dimensional hydrogen‐bonded networks, respectively.     

The conformational analyses of 2‐amino‐N‐[2‐(dimethylphenoxy)ethyl]propan‐1‐ol derivatives in different environments

Four crystal structures of 2‐amino‐N‐(dimethylphenoxyethyl)propan‐1‐ol derivatives, characterized by X‐ray diffraction analysis, are reported. The free base (R,S)‐2‐amino‐N‐[2‐(2,3‐dimethylphenoxy)ethyl]propan‐1‐ol, C₁₃H₂₁NO₂, 1 , crystallizes in the space group P2₁/n, with two independent molecules in the asymmetric unit. The hydrochloride, (S)‐N‐[2‐(2,6‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium chloride, C₁₃H₂₂NO₂⁺·Cl^?, 2c , crystallizes in the space group P2₁, with one cation and one chloride anion in the asymmetric unit. The asymmetric unit of two salts of 2‐picolinic acid, namely, (R,S)‐N‐[2‐(2,3‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium pyridine‐2‐carboxylate, C₁₃H₂₂NO₂⁺·C₆H₄NO₂^?, 1p , and (R)‐N‐[2‐(2,6‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium pyridine‐2‐carboxylate, C₁₃H₂₂NO₂⁺·C₆H₄NO₂^?, 2p , consists of one cation and one 2‐picolinate anion. Salt 1p crystallizes in the triclinic centrosymmetric space group P, while salt 2p crystallizes in the space group P4₁2₁2. The conformations of the amine fragments are contrasted and that of 2p is found to have an unusual antiperiplanar arrangement about the ether group. The crystal packing of 1 and 2c is dominated by hydrogen‐bonded chains, while the structures of the 2‐picolinate salts have hydrogen‐bonded rings as the major features. In both salts with 2‐picolinic acid, the specific R₁²(5) hydrogen‐bonding motif is observed. Structural studies have been enriched by the generation of fingerprint plots derived from Hirshfeld surfaces.     

An axial tert‐butyl group in strained cyclohexene: X‐ray analysis and theoretical calculations of 2‐(2‐tert‐butylcyclohex‐3‐enyl)propan‐2‐ol

The structure of the title compound, C₁₃H₂₄O, (I), shows a sofa conformation of the ring with two pseudo‐axial substituents. The dihedral angle between these substituents is 131.56 (12)°. Calculations using the B3LYP/6‐31G* level of theory show two minima, one corresponding to the crystal structure and the other to a boat conformation of the ring with two equatorial substituents. The energy of this latter conformation is 17.4 kcal mol⁻¹ higher than that of (I). The molecule forms an infinite co‐operative hydrogen‐bonded chain running in the b direction.     

1‐(9H‐Carbazol‐4‐yloxy)‐3‐{[2‐(2‐methoxyphenoxy)ethyl]amino}propan‐2‐ol hemihydrate: a carvedilol solvatomorph

In the title racemic hemihydrated solvatomorph of carvedilol (carv), C₂₄H₂₆N₂O₄·0.5H₂O, the asymmetric unit contains two independent organic moieties and one water molecule. Within this 2(carv)·H₂O unit, the molecular components are strongly linked by hydrogen bonds and the unit acts as the basic building block for the crystal structure. Interactions parallel to (10) generate hydrogen‐bonded layers which are further linked by much weaker C—H...N/O interactions. The conformations of the organic molecules, as well as the hydrogen‐bonding interactions connecting them, are compared with other related structures in the literature.     

Dual‐parameter correlations on rate of an aromatic nucleophilic substitution reaction in aqueous solutions of methanol,ethanol, and propan‐2‐ol

Reaction kinetics of 1‐chloro‐2,4‐dinitrobenzene with piperidine was studied spectrophotometrically in aqueous solutions of methanol, ethanol, and propan‐2‐ol at 25°C. The reaction in these solutions is not catalyzed by piperidine. The plots of second‐order rate constants of the reaction vs. mole fraction of water show maxima in the all‐aqueous solutions. Single‐parameter correlations of log k₂ vs. π* (dipolarity/polarizability), α (hydrogen‐bond donor acidity), and E_T^N (normalized polarity parameter) are very poor in the all solutions (for example, in aqueous solutions of ethanol, regression coefficients are 0.814, 0.113, and 0.486, respectively). Dual‐parameter correlations of log k₂ vs. π* and α in all cases represent significant improvement with regard to the single‐parameter models (in aqueous solutions of ethanol: n = 11, r = 0.980, and s = 0.034). Dipolarity/polarizability and hydrogen‐bond donor acidity (HBD) of media have opposite effects on the reaction rate. The activated complex leading to the zwitterionic intermediate is expected to be favored by increasing the solvent dipolarity/polarizability parameter. Increasing the hydrogen‐bond donor acidity of solvent stabilizes piperidine and hence the reaction rate decreases. A dual‐parameter equation of log k₂ vs. π* and α was obtained in the all‐aqueous solutions (n = 31, r = 0.956, s = 0.055) in which π* and α have approximately equal and opposite effects on the reaction rate. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 118–123, 2001     

2‐Amino‐5‐(3,4‐dimethoxybenzylidene)‐1‐methylimidazol‐4(5H)‐one N,N‐dimethylformamide monosolvate

The crystal structure of the title compound, C₁₃H₁₅N₃O₃·C₃H₇NO, was determined as part of a larger project focusing on creatinine derivatives as potential pharmaceuticals. The molecule is essentially planar, in part because of intramolecular hydrogen bonding. Inversion‐related pairs of molecules result from intermolecular hydrogen bonding. The π systems of 2‐amino‐5‐(3,4‐dimethoxybenzylidene)‐1‐methylimidazol‐4(5H)‐one and an inversion‐related molecule overlap slightly, indicating a small amount of π–π stacking. Bond lengths, angles and torsion angles are consistent with similar structures, except in the imidazolone ring near the doubly bonded C atom, where significant differences occur.     

Two succinic acid derivatives of 2‐ethyl‐6‐methylpyridin‐3‐ol

Crystals of bis(2‐ethyl‐3‐hydroxy‐6‐methylpyridinium) succinate–succinic acid (1/1), C₈H₁₂NO⁺·0.5C₄H₄O₄²⁻·0.5C₄H₆O₄, (I), and 2‐ethyl‐3‐hydroxy‐6‐methylpyridinium hydrogen succinate, C₈H₁₂NO⁺·C₄H₅O₄⁻, (II), were obtained by reaction of 2‐ethyl‐6‐methylpyridin‐3‐ol with succinic acid. The succinate anion and succinic acid molecule in (I) are located about centres of inversion. Intermolecular O—H...O, N—H...O and C—H...O hydrogen bonds are responsible for the formation of a three‐dimensional network in the crystal structure of (I) and a two‐dimensional network in the crystal structure of (II). Both structures are additionally stabilized by π–π interactions between symmetry‐related pyridine rings, forming a rod‐like cationic arrangement for (I) and cationic dimers for (II).     

3‐(4‐Bromo­phenyl)‐2‐(3,4‐di­hydro‐2H‐pyran‐5‐yl)‐1,1,1‐tri­fluoro­propan‐2‐ol

The molecular structure of the title compound, C₁₄H₁₄BrF₃O₂, adopts a bent conformation. Intramolecular O—H?F and intermolecular O—H?O interactions form a bifurcated hydrogen bond which produces a supramolecular assembly of head‐to‐tail dimers.     

2′‐(4‐Fluoro­phenyl)‐[1,2,3]­triazolo[4′,5′:16,17]­androst‐5‐en‐3β‐ol methanol hemisolvate

The asymmetric unit of the title compound, C₂₅H₃₀FN₃O·0.5CH₃OH, contains four symmetry‐independent steroid and two methanol mol­ecules. The conformations of the independent steroid mol­ecules are very similar. Intermolecular O—H⋯O hydrogen bonds create two independent chains, each of which links two of the independent steroid mol­ecules plus one methanol mol­ecule via a co‐operative O—H⋯O—H⋯O—H pattern. Intermolecular C—H⋯O and C—H⋯F interactions are also observed.     

A structural study of (1RS,2SR,3RS,4SR,5RS)‐2,4‐dibenzoyl‐1,3,5‐triphenylcyclohexan‐1‐ol chloroform hemisolvate and (1RS,2SR,3RS,4SR,5RS)‐2,4‐dibenzoyl‐1‐phenyl‐3,5‐bis(2‐methoxyphenyl)cyclohexan‐1‐ol

(1RS,2SR,3RS,4SR,5RS)‐2,4‐Dibenzoyl‐1,3,5‐triphenylcyclohexan‐1‐ol or (4‐hydroxy‐2,4,6‐triphenylcyclohexane‐1,3‐diyl)bis(phenylmethanone), C₃₈H₃₂O₃, (1), is formed as a by‐product in the NaOH‐catalyzed synthesis of 1,3,5‐triphenylpentane‐1,5‐dione from acetophenone and benzaldehyde. Single crystals of the chloroform hemisolvate, C₃₈H₃₂O₃·0.5CHCl₃, were grown from chloroform. The structure has triclinic (P) symmetry. One diastereomer [as a pair of (1RS,2SR,3RS,4SR,5RS)‐enantiomers] of (1) has been found in the crystal structure and confirmed by NMR studies. The dichoromethane hemisolvate has been reported previously [Zhang et al. (2007). Acta Cryst. E 63 , o4652]. (1RS,2SR,3RS,4SR,5RS)‐2,4‐Dibenzoyl‐3,5‐bis(2‐methoxyphenyl)‐1‐phenylcyclohexan‐1‐ol or [4‐hydroxy‐2,6‐bis(2‐methoxyphenyl)‐4‐phenylcyclohexane‐1,3‐diyl]bis(phenylmethanone), C₄₀H₃₆O₅, (2), is also formed as a by‐product, under the same conditions, from acetophenone and 2‐methoxybenzaldehyde. Crystals of (2) have been grown from chloroform. The structure has orthorhombic (Pca2₁) symmetry. A diastereomer of (2) possesses the same configuration as (1). In both structures, the cyclohexane ring adopts a chair conformation with all bulky groups (benzoyl, phenyl and 2‐methoxyphenyl) in equatorial positions. The molecules of (1) and (2) both display one intramolecular O—H...O hydrogen bond.     

Hydrogen‐bonded structures of the isomeric compounds of quinoline with 2‐chloro‐5‐nitrobenzoic acid, 3‐chloro‐2‐nitrobenzoic acid, 4‐chloro‐2‐nitrobenzoic acid and 5‐chloro‐2‐nitrobenzoic acid

The structures of four isomeric compounds, all C₇H₄ClNO₄·C₉H₇N, of quinoline with chloro‐ and nitro‐substituted benzoic acid, namely, 2‐chloro‐5‐nitrobenzoic acid–quinoline (1/1), (I), 3‐chloro‐2‐nitrobenzoic acid–quinoline (1/1), (II), 4‐chloro‐2‐nitrobenzoic acid–quinoline (1/1), (III), and 5‐chloro‐2‐nitrobenzoic acid–quinoline (1/1), (IV), have been determined at 185 K. In each compound, a short hydrogen bond is observed between the pyridine N atom and a carboxyl O atom. The N...O distances are 2.6476 (13), 2.5610 (13), 2.5569 (12) and 2.5429 (12) Å for (I), (II), (III) and (IV), respectively. Although in (I) the H atom in the hydrogen bond is located at the O site, in (II), (III) and (IV) the H atom is disordered in the hydrogen bond over two positions with (N site):(O site) occupancies of 0.39 (3):0.61 (3), 0.47 (3):0.53 (3) and 0.65 (3):0.35 (3), respectively.     

catena‐Poly[[[tetrakis(μ‐acetato‐κ2O:O′)dirhodium(II)]‐μ‐[1,3‐bis(dimethylamino)propan‐2‐ol‐κ2N:N′]] tetrahydrofuran hemisolvate]

In the structure of the title compound, {[Rh₂(C₂H₃O₂)₄(C₇H₁₈N₂O)]·0.5C₄H₈O}_n or {[Rh₂(O₂CMe)₄(Hbdmap)]·0.5C₄H₈O}_n, where Hbdmap is 1,3‐bis­(dimethyl­amino)propan‐2‐ol, each Hbdmap ligand is coordinated to two [Rh₂(O₂CMe)₄] units by two N atoms, resulting in a polymeric chain structure. The observed coordination mode of the Hbdmap mol­ecule is unprecedented.     

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.     

(R)‐4‐(4‐Fluoro­phenyl)‐1‐[2‐hydroxy‐2‐(3‐methyl‐1‐benzo­furan‐2‐yl)­ethyl]­piperazinium chloride propan‐1‐ol solvate

The title compound, C₂₁H₂₄FN₂O₂⁺·Cl⁻·C₃H₈O, is a potential drug designed as a hybrid compound with antihypertensive, antioxidant and β‐adrenolytic activity. The cation contains nearly planar benzo­furan and fluoro­phenyl ring systems, as well as a piperazine ring adopting an almost perfect chair conformation. The benzo­furan and piperazine moieties are connected by an ethyl chain, the moieties forming a dihedral angle of 163.12 (13)°. In the crystal structure, ions and propanol solvent mol­ecules are linked via N—H⋯Cl and O—H⋯Cl bonds into linear (010) chains.     

Hydrogen‐bonded structures of the isomeric compounds of phthalazine with 3‐chloro‐2‐nitrobenzoic acid, 4‐chloro‐2‐nitrobenzoic acid and 4‐chloro‐3‐nitrobenzoic acid

The structures of three isomeric compounds, C₇H₄ClNO₄·C₈H₆N₂, of phthalazine with chloro‐ and nitro‐substituted benzoic acid, namely, 3‐chloro‐2‐nitrobenzoic acid–phthalazine (1/1), (I), 4‐chloro‐2‐nitrobenzoic acid–phthalazine (1/1), (II), and 4‐chloro‐3‐nitrobenzoic acid–phthalazine (1/1), (III), have been determined at 190 K. In the asymmetric unit of each compound, there are two crystallographically independent chloronitrobenzoic acid–phthalazine units, in each of which the two components are held together by a short hydrogen bond between an N atom of the base and a carboxyl O atom. In one hydrogen‐bonded unit of (I) and in two units of (II), a weak C—H...O interaction is also observed between the two components. The N...O distances are 2.5715 (15) and 2.5397 (17) Å for (I), 2.5655 (13) and 2.6081 (13) Å for (II), and 2.613 (2) and 2.589 (2) Å for (III). In both hydrogen‐bonded units of (I) and (II), the H atoms are each disordered over two positions with (N site):(O site) occupancies of 0.35 (3):0.65 (3) and 0.31 (3):0.69 (3) for (I), and 0.32 (3):0.68 (3) and 0.30 (3):0.70 (3) for (II). The H atoms in the hydrogen‐bonded units of (III) are located at the O‐atom sites.     

Three tetrahydro‐1,4‐epoxy‐1‐benzazepines carrying pendent heterocyclic substituents: supramolecular structures in zero,one or two dimensions

(2SR,4RS)‐7‐Fluoro‐2‐exo‐(2‐furyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₄H₁₂FNO₂, (I), crystallizes with Z′ = 2 in the space group P2₁/c. A combination of three C—H...O hydrogen bonds and one C—H...N hydrogen bond links the molecules into a complex chain of rings, and pairs of such chains are linked into a tube‐like structure by two C—H...π(arene) hydrogen bonds. There are no hydrogen bonds in the structure of racemic (2SR,4RS)‐2‐exo‐(5‐bromo‐2‐thienyl)‐7‐fluoro‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₄H₁₁BrFNOS, (II), while the molecules of (2S,4R)‐2‐exo‐(5‐bromo‐2‐thienyl)‐7‐trifluoromethoxy‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₅H₁₄BrF₃NO₂S, (III), are linked into sheets by a combination of two C—H...O hydrogen bonds and one C—H...π(arene) hydrogen bond. The significance of this study lies in its observation of the wide variation in the patterns of supramolecular aggregation, consequent upon modest changes in the peripheral substituents.     

Conformational studies of hydantoin‐5‐acetic acid and orotic acid

Hydantoin‐5‐acetic acid [2‐(2,5‐dioxoimidazolidin‐4‐yl)acetic acid] and orotic acid (2,6‐dioxo‐1,2,3,6‐tetrahydropyrimidine‐4‐carboxylic acid) each contain one rigid acceptor–donor–acceptor hydrogen‐bonding site and a flexible side chain, which can adopt different conformations. Since both compounds may be used as coformers for supramolecular complexes, they have been crystallized in order to examine their conformational preferences, giving solvent‐free hydantoin‐5‐acetic acid, C₅H₆N₂O₄, (I), and three crystals containing orotic acid, namely, orotic acid dimethyl sulfoxide monosolvate, C₅H₄N₂O₄·C₂H₆OS, (IIa), dimethylammonium orotate–orotic acid (1/1), C₂H₈N⁺·C₅H₃N₂O₄⁻·C₅H₄N₂O₄, (IIb), and dimethylammonium orotate–orotic acid (3/1), 3C₂H₈N⁺·3C₅H₃N₂O₄⁻·C₅H₄N₂O₄, (IIc). The crystal structure of (I) shows a three‐dimensional network, with the acid function located perpendicular to the ring. Interestingly, the hydroxy O atom acts as an acceptor, even though the carbonyl O atom is not involved in any hydrogen bonds. However, in (IIa), (IIb) and (IIc), the acid functions are only slightly twisted out of the ring planes. All H atoms of the acidic functions are directed away from the rings and, with respect to the carbonyl O atoms, they show an antiperiplanar conformation in (I) and synperiplanar conformations in (IIa), (IIb) and (IIc). Furthermore, in (IIa), (IIb) and (IIc), different conformations of the acid O=C—C—N torsion angle are observed, leading to different hydrogen‐bonding arrangements depending on their conformation and composition.