4‐Oxo­cyclo­hexane­carboxyl­ic acid: hydrogen bonding in the monohydrate of a δ‐keto acid

The title monohydrate, C₇H₁₀O₃·H₂O, aggregates as a complex hydrogen‐bonding network, in which the water mol­ecule accepts a hydrogen bond from the carboxyl group of one mol­ecule and donates hydrogen bonds to ketone and carboxyl Czdbnd;O functions in two additional mol­ecules, yielding a sheet‐like structure of parallel ribbons. The keto acid adopts a chiral conformation through rotation of the carboxyl group by 62.50 (15)° relative to the plane defined by its point of attachment and the ketone C and O atoms. Two C—H⋯O close contacts exist in the structure.     

2‐Pyridone–tartronic acid (1/1), 3‐hydroxy­pyridinium hydrogen tartronate and 4‐hydroxy­pyridinium hydrogen tartronate

Tartronic acid forms a hydrogen‐bonded complex, C₅H₅NO·C₃H₄O₅, (I), with 2‐pyridone, while it forms acid salts, namely 3‐hydroxy­pyridinium hydrogen tartronate, (II), and 4‐hy­droxy­pyridinium hydrogen tartronate, (III), both C₅H₆NO⁺·C₃H₃O₅⁻, with 3‐hydroxy­pyridine and 4‐hydroxy­pyridine, respectively. In (I), the pyridone mol­ecules and the acid mol­ecules form R(8) and R(10) hydrogen‐bonded rings, respectively, around the inversion centres. In (II) and (III), the cations and anions are linked by N—H⋯O and O—H⋯O hydrogen bonds to form a hydrogen‐bonded chain. In each of (I), (II) and (III), an intermolecular hydrogen bond is formed between a carboxyl group and the hydroxyl group attached to the central C atom, and in (I), the hydroxyl group participates in an intramolecular hydrogen bond with a carbonyl group. No intermolecular hydrogen bond is formed between the carboxyl groups in (I), or between the carboxyl and carboxyl­ate groups in (II) and (III).     

7‐Oxobi­cyclo­[2.2.1]­heptane‐1‐carboxylic acid and ()‐7‐oxobi­cyclo­[2.2.1]­hept‐5‐ene‐2‐endo‐carboxylic acid: hydrogen bonding in two norbornyl keto acids

Molecules of the title β‐keto acid, 7‐oxobi­cyclo­[2.2.1]­heptane‐1‐carboxylic acid, C₈H₁₀O₃, exhibit chirality due to the bridgehead carboxyl group, which is partially ordered and has a slightly asymmetric conformation. The mol­ecules form centrosymmetric hydrogen‐bonded carboxyl dimers [O?O 2.639 (2) Å]. The title alkenoic γ‐keto acid, ()‐7‐oxobi­cyclo­[2.2.1]­hept‐5‐ene‐2‐endo‐carboxylic acid, C₈H₈O₃, also forms typical centrosymmetric hydrogen‐bonded carboxyl dimers [O?O 2.660 (3) Å]. There is partial disorder of the carboxyl group in each compound.     

(+)‐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.     

(±)‐(2,3,4,4a,5,6,7,8‐Octa­hydro‐2‐oxo­naphthalen‐1‐yl)acetic acid: hydrogen‐bonding pattern of the mono­hydrate of an unsaturated bicyclic γ‐keto acid

In the title compound, C₁₂H₁₆O₃·H₂O, the water of hydration accepts a hydrogen bond from the carboxyl group and donates hydrogen bonds to the carboxyl carbonyl and the ketone groups of two different neighbors, yielding a complex three‐dimensional hydrogen‐bonding array. There are two independent hydrated mol­ecules in the asymmetric unit (Z′ = 2) related by a pseudo‐translation.     

catena‐Poly[[[cis‐aqua­bis(4‐carboxy­cyclo­hexane‐1‐carboxyl­ato‐κ2O,O′)cadmium(II)]‐μ‐4,4′‐bipyridine‐κ2N:N] monohydrate]

The title complex, {[Cd(C₈H₁₁O₄)₂(C₁₀H₈N₂)(H₂O)]·H₂O}_n, consists of linear chains formed through 4,4′‐bipyridine ligands linking seven‐coordinated Cd^II ions. Each Cd^II ion is in a distorted penta­gonal–bipyramidal environment, coordinated by one water ligand, two 4‐carboxy­cyclo­hexane‐1‐carboxyl­ate ligands and one bridging 4,4′‐bipyridine ligand to generate linear chains. The water mol­ecules and the Cd atom on one side, and the 4,4′‐bipyridine unit on the other, are bisected by two sets of twofold axes. The carboxylate group of the 4‐carboxy­cyclo­hexane‐1‐carboxyl ligand chelates a Cd^II ion, while the (protonated) carboxyl group forms hydrogen bonds with adjacent chains, resulting in a layered structure. This is the first reported occurrence of a dicarboxycyclo­hexane ligand exhibiting a non‐bridging coordination mode.     

(+)‐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.     

(–)‐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)°].     

(±)‐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.     

From α‐carbamoyl‐α‐cyano­oxiranes to 3‐halogenopyruv­amides

The crystal structures of the first stable α‐diol from the α‐halogenopyruv­amide series, 3‐chloro‐2,2‐di­hydroxy‐3‐phenyl­propan­amide, C₉H₁₀­ClNO₃, and three products [3‐(4‐chloro­phenyl)‐2‐cyano‐2,3‐epoxy­propan­amide, C₁₀H₇­ClN₂O₂, 3‐bromo‐2‐cyano‐2‐hydroxy‐3‐p‐tolyl­propan­amide, C₁₁H₁₁Br­N₂O₂, 3‐bromo‐2‐oxo‐3‐p‐tolyl­propan­amide, C₁₀H₁₀­BrNO₂] obtained during the systematic synthesis of α‐halogenopyruv­amides are reported. The crystal structures are dominated by hydrogen bonds involving an amide group. The stability of the geminal diol could be ascribed to hydrogen bonds which involve both hydroxyl groups.     

(+)‐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.     

(−)‐3,7‐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.     

()‐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.     

Derivatives of substituted 3‐trichlorogermylpropionic acid

The central Ge atoms in the structures of 3‐(2‐fluoro­phenyl)‐3‐(tri­phenyl­germyl)­propionic acid, [Ge(C₆H₅)₃(C₉H₈FO₂)], 3‐(2‐tolyl)‐3‐(tri‐4‐tolyl­germyl)­propionic acid, [Ge(C₇H₇)₃(C₁₀H₁₁O₂)], and 3‐(4‐tolyl)‐3‐(tri­benzyl­germyl)­propionic acid, [Ge(C₇H₇)₃(C₁₀H₁₁O₂)], are four‐coordinate with slightly distorted tetrahedral geometry. The Ge—Csp³ distances [1.970 (3)–1.997 (3) Å] are significantly longer than the Ge—C_aromatic distances [1.940 (3)–1.959 (2) Å]. In all three structures, the mol­ecules form dimeric pairs about inversion centres through strong hydrogen‐bonding interactions between carboxyl­ic acid groups.     

(±)‐7‐Oxo‐1,2,3,4,4a,5,6,7‐octa­hydro­naphthalene‐1‐acetic acid: catemeric hydrogen bonding and diastereomeric disorder in a bicyclic unsaturated ɛ‐keto acid

The 68.5:31.5 mixture of diastereoisomers obtained in the synthesis of the title compound, C₁₂H₁₆O₃, yielded sharply melting crystals containing the same ratio of epimers, in a disordered crystallographic arrangement. The disorder resides almost entirely in the carboxy­methyl side chain, but places the two sets of carboxyl O atoms at nearly identical paired spatial positions. Neither component displays significant carboxyl disorder, and the mol­ecules aggregate as hydrogen‐bonded carboxyl‐to‐ketone catemers [O⋯O = 2.673 (4) Å and O—H⋯O = 158°] having glide‐related components, with centro­symmetrically related pairs of chains following axes perpendicular to b. Close intermolecular C—H⋯O contacts exist for both the ketone and the carboxyl group. The energetics of the epimers and of their crystallization mode are discussed.     

Disordered syn–anti hydrogen‐bonded chains in 3‐(ferrocenyl­carbonyl)­propionic acid

The title compound, [Fe(C₅H₅)(C₉H₉O₃)], has Fe–centroid distances of 1.6551 (11) and 1.6445 (11) Å to the cyclo­penta­dienyl rings. The carboxyl group forms hydrogen bonds in the extremely rare syn–anti chain motif, with O⋯O distances of 2.667 (3) and 2.655 (3) Å. The carboxyl group and the hydrogen‐bonded chains are disordered.