()‐3‐Oxo­cyclo­hexane­carboxyl­ic and ‐acetic acids: contrasting hydrogen‐bonding patterns in two homologous keto acids

The crystal structures for the title compounds reveal fundamentally different hydrogen‐bonding patterns. ()‐3‐Oxo­cyclo­hexanecarboxylic acid, C₇H₁₀O₃, displays acid‐to‐ketone catemers having a glide relationship for successive components of the hydrogen‐bonding chains which advance simultaneously by two cells in a and one in c [O?O = 2.683 (3) Å and O—H?O = 166°]. A pair of intermolecular close contacts exists involving the acid carbonyl group. The asymmetric unit in ()‐3‐oxo­cyclo­hexane­acetic acid, C₈H₁₂O₃, utilizes only one of two available isoenthalpic conformers and its aggregation involves mutual hydrogen bonding by centrosymmetric carboxyl dimerization [O?O = 2.648 (3) Å and O—H?O = 171°]. Intermolecular close contacts exist for both the ketone and the acid carbonyl group.     

(+)‐Gibberellin C: hydrogen‐bonding pattern of the monohydrate of a non‐racemic pentacyclic diterpenoid

In the monohydrate of the title compound, (+)‐2β,4aα‐di­hydroxy‐1,7‐di­methyl‐8‐oxo‐4bβ,7α‐gibbane‐1α,10β‐di­carb­ox­yl­ic acid‐1,4a‐lactone, C₁₉H₂₄O₆·H₂O, intermolecular hydrogen bonding progresses helically along b from carboxyl to ketone [O?O = 2.694 (5) Å]. The carboxyl and lactone carbonyl groups in translationally related mol­ecules within a helix both accept hydrogen bonds from the same water of hydration. The oxy­gen of this water in turn accepts a hydrogen bond from the hydroxyl group of a third screw‐related mol­ecule in an adjacent counterdirectionally oriented helix, yielding a complex three‐dimensional hydrogen‐bonding array. Intermolecular O?H—C close contacts were found to the carboxyl and lactone carbonyls, the hydroxyl, and the water.     

(–)‐Dioxosantadienic acid: hydrogen‐bonding patterns in a bicyclic sesquiterpenoid keto acid and its mono­hydrate

The an­hydrous form, (I), of the title compound, (?)‐2‐(1,2,3,4,4a,7‐hexa­hydro‐4a,8‐di­methyl‐1,7‐dioxo‐2‐naphthyl)­propionic acid, C₁₅H₁₈O₄, derived from a naturally occurring sesquiterpenoid, has two mol­ecules in the asymmetric unit, (I) and (I′), differing in the conformations of the saturated ring and the carboxyl group. The compound aggregates as carboxyl‐to‐ketone hydrogen‐bonding catemers [O?O = 2.776 (3) and 2.775 (3) Å]. Two crystallographically independent sets of single‐strand hydrogen‐bonding helices with opposite end‐to‐end orientation pass through the cell in the b direction, one consisting exclusively of mol­ecules of (I) and the other entirely of (I′). Three C—H?O=C close contacts are found in (I). The monohydrate, C₁₅H₁₈O₄·H₂O, (II), with two mol­ecules of (I) plus two water mol­ecules in its asymmetric unit, forms a complex three‐dimensional hydrogen‐bonding network including acid‐to‐water, water‐to‐acid, water‐to‐ketone, water‐to‐water and acid‐to‐acid hydrogen bonds, plus three C—H?O=C close contacts. In both (I) and (II), only the ketone remote from the acid is involved in hydrogen bonding.     

(+)‐3‐Oxo‐4‐pregnene‐20β‐carboxyl­ic acid: catemeric hydrogen bonding in a steroidal keto acid

The title keto acid, (+)‐23,24‐dinor‐3‐oxo­chol‐4‐en‐22‐oic acid, C₂₂H₃₂O₃, forms carboxyl‐to‐ketone hydrogen‐bonding catemers [O?O = 2.699 (4) Å and O—H?O = 173°], linking mol­ecules screw‐related in b. The four mol­ecules in the cell form two parallel counter‐directional chains, screw‐related in a. Intermolecular C—H?O=C close contacts to different neighboring mol­ecules were found for the ketone and the acid.     

(+)‐3,11‐Dioxoandrost‐4‐ene‐17β‐carboxyl­ic acid: catemeric hydrogen bonding in a steroidal keto acid

The title keto acid, C₂₀H₂₆O₄, forms carboxyl‐to‐ketone hydrogen‐bonding catemers [O?O = 2.653 (5) Å and O—H?O = 172 (5)°], linking translationally related mol­ecules via the A‐ring ketone. The two mol­ecules in the cell form two parallel counter‐directional chains, screw‐related in b. A total of four intermolecular C—H?O=C close contacts was found, involving both ketone functions.     

(+)‐Camphor­acetic acid: catemeric hydrogen bonding in a γ‐keto acid

The title compound, (1R)‐4,7,7‐tri­methyl‐3‐oxobi­cyclo­[2.2.1]­heptane‐2‐endo‐acetic acid, C₁₂H₁₈O₃, like its lower homolog, forms carboxyl‐to‐ketone hydrogen‐bonding catemers (Z′ = 2) [O⋯O = 2.729 (5) and 2.707 (5) Å, and O—H⋯O = 165 and 170°] with screw‐related components. The two mol­ecules of the asymmetric unit differ slightly in conformation and produce two counter‐aligned hydrogen‐bonding chains, both aligned with the b axis. Close intermolecular C—H⋯O=C contacts exist for the ketone group of one mol­ecule and for both the ketone and carboxyl functions in the other.     

9α‐Fluoro‐16α‐methyl‐3,11‐dioxoandrosta‐1,4‐diene‐17β‐carboxyl­ic acid: catemeric hydrogen bonding and acetic acid solvation in a steroidal keto acid related to dexamethasone

The title keto acid crystallizes as a solvate, C₂₁H₂₅FO₄·C₂H₄O₂, with two mol­ecules each of steroid and acetic acid per asymmetric unit. The former are approximately parallel, with opposite end‐to‐end orientation, and form translational carboxyl‐to‐ketone hydrogen‐bonding catemers [O⋯O = 2.679 (6) and 2.650 (5) Å, and O—H⋯O = 165 and 162°] that involve the 3‐ketone group and follow the a axis. The acetic acid mol­ecules are paired by hydrogen bonding, and neither they nor the F atom nor the 11‐ketone group play any overt role in the hydrogen‐bonding scheme of the steroid. Intermolecular C—H⋯O=C close contacts involving three different neighboring mol­ecules exist to the 11‐ketone group, the steroidal carboxyl group and one of the acetic acid molecules.     

(±)‐cis‐2‐Methyl‐4‐oxo­cyclo­hexane­carboxyl­ic acid: catemeric hydrogen bonding in a δ‐keto acid derived from Hagemann's ester

The title compound, C₈H₁₂O₃, crystallizes as acid‐to‐ketone hydrogen‐bonding catemers, in which hydrogen bonds progress from the carboxyl group of each mol­ecule to the ketone group of a translationally related neighbor [O⋯O = 2.738 (3) Å and O—H⋯O = 153 (4)°]. Four separate hy­drogen‐bonding chains proceed through the cell in centrosymmetrically related pairs along axes lying in the ab plane. Three intermolecular C—H⋯O close contacts exist involving both carboxyl O atoms. Factors contributing to the choice of hydrogen‐bonding mode are discussed.     

(+)‐2‐(1,2,3,4,4a,5,6,7‐Octa­hydro‐4a,8‐di­methyl‐7‐oxo‐2‐naphthyl)­propionic acid: catemeric hydrogen bonding in a bicyclic sesquiterpenoid keto acid

The title compound, C₁₅H₂₂O₃, derived from a naturally occurring sesquiterpenoid, has two mol­ecules in the asymmetric unit, differing principally in the rotational conformation of the carboxyl group. Each species aggregates separately as a carboxyl‐to‐ketone hydrogen‐bonding catemer [O?O = 2.752 (4) and 2.682 (4) Å, and O—H?O = 161 (4) and 168 (4)°], producing two crystallographically independent single‐strand hydrogen‐bonding helices, with opposite end‐to‐end orientations, passing through the cell in the b direction. Three intermolecular C—H?O=C close contacts exist for the ketone.     

(–)‐2‐(1,2,3,4,4a,5,6,7,8,8aα‐Decahydro‐4aβ,8α‐dimethyl‐7‐oxo‐2β‐naphthyl)propionic acid: catemeric hydrogen bonding in a bicyclic sesquiterpenoid ζ‐keto acid

In the title compound, C₁₅H₂₄O₃, derived from a naturally occurring sesquiterpenoid, the asymmetric unit consists of two mol­ecules differing by 167.4 (8)° in the rotational conformation of the carboxyl group. Each molecule aggregates separately with its own type as carboxyl‐to‐ketone hydrogen‐bonding catemers [O⋯O = 2.715 (6) and 2.772 (6) Å, and O—H⋯O = 169 and 168°]. This generates two crystallographically independent single‐strand hydrogen‐bonding helices passing through the cell in the b direction, with opposite end‐to‐end orientations. One intermolecular C—H⋯O=C close contact exists for the carboxyl group of one of the mol­ecules. The structure is isostructural with that of a closely related unsaturated keto acid reported previously.     

The epimeric 9‐oxobicyclo[3.3.1]nonane‐3‐carboxylic acids: hydrogen‐bonding patterns of the endo acid and the lactol of the exo acid

The two δ‐keto carboxylic acids of the title, both C₁₀H₁₄O₃, are epimeric at the site of carboxyl attachment. The endo (3α) epimer, (I), has its keto‐acid ring in a boat conformation, with the tilt of the carboxyl group creating conformational chirality. The mol­ecules form hydrogen bonds by centrosymmetric pairing of carboxyl groups across the corners of the chosen cell [O⃛O = 2.671 (2) Å and O—H⃛O = 179 (2)°]. Two close intermolecular C—H⃛O contacts exist for the ketone. The exo (3β) epimer exists in the closed ring–chain tautomeric form as the lactol, 8‐hydroxy‐9‐oxatri­cyclo­[5.3.1.0^3,8]­undecan‐10‐one, (II). The mol­ecules have conformational chirality, and the hydrogen‐bonding scheme involves intermolecular hydroxyl‐to‐carbonyl chains of mol­ecules screw‐related in b [O⃛O = 2.741 (2) Å and O—H⃛O = 177 (2)°].     

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.     

(−)‐3,7‐Dioxo‐5β‐cholanic acid: dual hydrogen‐bonding modes in a diketonic bile‐acid derivative

The asymmetric unit of the title compound, C₂₄H₃₆O₄, contains three mol­ecules, all differing in their side‐chain conformations and all linked by hydrogen bonding confined entirely within a three‐mol­ecule block. One connection is of the acid‐to‐ketone type [O⋯O = 2.7055 (19) Å and O—H⋯O = 180°] and the other involves carboxyl pairing [O⋯O = 2.6485 (18) and 2.6598 (18) Å, and O—H⋯O = 168 and 174°]. Numerous inter­molecular C—H⋯O close contacts connect neighbouring mol­ecules.     

Hydro­gen‐bonded adducts of ferrocene‐1,1′‐diyl­bis­(di­phenyl­methanol): a finite cyclic 1:1 adduct with 2,2′‐dipyridyl­amine

In ferrocene‐1,1′‐diyl­bis­(di­phenyl­methanol)–2,2′‐dipyridyl­amine (1/1), [Fe(C₁₈H₁₅O)₂]·C₁₀H₉N₃, (I), there is an intramolecular O—H?O hydrogen bond [H?O 2.03 Å, O?O 2.775 (2) Å and O—H?O 147°] in the ferrocenediol component, and the two neutral molecular components are linked by one O—H?N hydrogen bond [H?N 1.96 Å, O?N 2.755 (2) Å and O—H?N, 157°] and one N—H?O hydrogen bond [H?O 2.26 Å, N?O 3.112 (2) Å and N—H?O 164°] forming a cyclic R(8) motif. One of the pyridyl N atoms plays no part in the intermolecular hydrogen bonding, but participates in a short intramolecular C—H?N contact [H?N 2.31 Å, C?N 2.922 (2) Å and C—H?N 122°].     

Two diastereomers of ()‐cis‐2‐(3‐oxo‐1,3,4,5,6,7‐hexa­hydro­isobenzo­furan‐1‐yl)cyclo­hexane­carboxyl­ic acid

The structures are presented for both diastereomers of the title compound, C₁₅H₂₀O₄, produced by base‐catalyzed self‐condensation of cyclo­hexane‐cis‐1,2‐di­carboxyl­ic anhydride in refluxing triethyl­amine. Equilibration of either diastereomer under the condensation conditions yielded the same 5:3 mixture. In the crystal, one diastereomer, (II), is ordered, while the other, (I), displays both flexional ring disorder and carboxyl disorder; both aggregate as centrosymmetric hydrogen‐bonded dimers [for (I), O?O = 2.680 (2) Å; for (II), O?O = 2.635 (4) Å].     

1′‐Acetyl­ferrocene‐1‐carboxyl­ic acid: an instance of hydrogen bonding in the rare dimeric acid‐to‐ketone mode

The title compound, [Fe(C₆H₅O₂)(C₇H₇O)], adopts a conformation involving partial staggering of its rings and aggregates in the solid as acid‐to‐ketone hydrogen‐bonding dimers [O?O = 2.720 (4) Å and O—H?O = 164°] having centro­symmetrically related components. Close intermolecular C—H?O contacts were found to both carboxyl O atoms.     

()‐12‐Oxotri­cyclo­[6.2.2.01,6]­dodec­ane‐10‐carboxyl­ic acid: hydrogen bonding in a tricyclic δ‐keto acid

The ring system of the title compound, C₁₃H₁₈O₃, was synthesized by addition of ethyl acryl­ate to the dien­amine of 2‐octalone. The keto acid aggregates in the solid as acid‐to‐acid dimers [O?O = 2.663 (2) Å and O—H?O = 170 (3)°] whose centrosymmetric hydrogen bonds lie across the a edges and the center of the chosen cell. Three intermolecular C—H?O close contacts within 2.7 Å were found involving the ketone group.     

Adducts of 1,1,1‐tris(4‐hydroxyphenyl)ethane with diamines: three‐dimensional hydrogen‐bonded frameworks formed with 1,6‐diaminohexane and 2,2′‐bipyridyl

The adduct 1,6‐di­amino­hexane–1,1,1‐tris(4‐hydroxy­phenyl)­ethane (1/2) is a salt {hexane‐1,6‐diyldiammonium–4‐[1,1‐bis(4‐hydroxyphenyl)ethyl]phenolate (1/2)}, C₆H₁₈N₂²⁺·2C₂₀H₁₇O₃^?, in which the cation lies across a centre of inversion in space group P. The anions are linked by two short O—H?O hydrogen bonds [H?O 1.74 and 1.76 Å, O?O 2.5702 (12) and 2.5855 (12) Å, and O—H?O 168 and 169°] into a chain containing two types of R(24) ring. Each cation is linked to four different anion chains by three N—H?O hydrogen bonds [H?O 1.76–2.06 Å, N?O 2.6749 (14)–2.9159 (14) Å and N—H?O 156–172°]. In the adduct 2,2′‐bipyridyl–1,1,1‐tris(4‐hydroxy­phenyl)­ethane (1/2), C₁₀H₈N₂·2C₂₀H₁₈O₃, the neutral di­amine lies across a centre of inversion in space group P2₁/n. The tris­(phenol) mol­ecules are linked by two O—H?O hydrogen bonds [H?O both 1.90 Å, O?O 2.7303 (14) and 2.7415 (15) Å, and O—H?O 173 and 176°] into sheets built from R(38) rings. Pairs of tris­(phenol) sheets are linked via the di­amine by means of a single O—H?N hydrogen bond [H?N 1.97 Å, O?N 2.7833 (16) Å and O—H?N 163°].     

5‐Methyl‐2‐thiouracil

The molecular structure of the title compound, also known as 2‐thio­thymine [systematic name: 2,3‐di­hydro‐5‐methyl‐2‐thioxopyrimidin‐4(1H)‐one], C₅H₆N₂OS, is similar to that of thymine, with only small changes in the ring structure, apart from a significant difference at the substitution site [S=C = 1.674 (1) Å]. The mol­ecules are connected by hydrogen bonds, with N—H?O = 2.755 (2) Å and N—H?S = 3.352 (1) Å. The hydrogen‐bond network is different from that in thymine, since it involves all the donor and acceptor atoms.     

2‐Amino‐4‐(4‐pyridyl)­pyrimidine and the 1:1 adduct with 4‐amino­benzoic acid

The structure of the title compound, C₉H₈N₄, comprises non‐planar mol­ecules that associate via pyrimidine N—H?N dimer R(8) hydrogen‐bonding associations [N?N 3.1870 (17) Å] and form linear hydrogen‐bonded chains via a pyrimidine N—H?N(pyridyl) interaction [N?N 3.0295 (19) Å]. The dihedral angle between the two rings is 24.57 (5)°. The structure of the 1:1 adduct with 4‐amino­benzoic acid, C₉H₈N₄·C₇H₇NO₂, exhibits a hydrogen‐bond­ing network involving COOH?N(pyridyl) [O?N 2.6406 (17) Å], pyrimidine N—H?N [N?N 3.0737 (19) and 3.1755 (18) Å] and acid N—H?O interactions [N?O 3.0609 (17) and 2.981 (2) Å]. The dihedral angle between the two linked rings of the base is 38.49 (6)° and the carboxyl­ic acid group binds to the stronger base group in contrast to the (less basic) complementary hydrogen‐bonding site.