Conformational enantiomeric disorder in tripivaloylmethane

Kaitner, Branko; Stilinović, Vladimir

doi:10.1107/s0108270107012474

Cited by 5 publications

(5 citation statements)

References 8 publications

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“…Substitutional disorder between enantiomers of the same molecule have been reported before (Chulvi et al, 2015;Kaitner & Stilinović, 2007;Evain et al, 2003). The crystal structure of the racemic compound 5-(3-hydroxy-3-methylbut-1-ynyl)-3-(1-methylpyrrolidin-2-yl)pyridine (Evain et al, 2003) shows the two enantiomers in the asymmetric unit and substitutional disorder of the kind observed here, with one conformer of one enantiomer disordered at the site of the other enantiomer in a roughly 4:1 proportion, with parts of the two molecules showing exact overlap.…”

Section: Resultsmentioning

confidence: 69%

Observation of an infrequent enantiomer/conformer substitutional disorder in ethyl 13-ethyl-4-oxo-8,13-dihydro-4H-benzo[5,6]azepino[3,2,1-ij]quinoline-5-carboxylate heptane hemisolvate

et al. 2018

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Considering the importance of quinolones due to their broad spectrum of biological activities, the crystal structure of the title compound, C22H21NO3·0.5C7H16, has been determined. Two enantiomers of the benzazepinoquinoline molecule and one molecule of heptane form the asymmetric unit of this centrosymmetric triclinic (P\overline{1}) crystal. All the molecules in the crystal present disorder. Substitutional disorder is observed for the benzazepine molecules, where a minority conformer of the R enantiomer replaces the main conformer of the S enantiomer and vice versa. Positional disorder is found for the heptane solvent molecule, which occupies a void left by the independent enantiomers of both conformers.

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Section: Resultsmentioning

confidence: 69%

Observation of an infrequent enantiomer/conformer substitutional disorder in ethyl 13-ethyl-4-oxo-8,13-dihydro-4H-benzo[5,6]azepino[3,2,1-ij]quinoline-5-carboxylate heptane hemisolvate

et al. 2018

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“…Compound 1 provides an ordered racemic crystal structure which presents enantiomeric disorder in its crystalline structure, 14,15 conferring to this compound high structural interest. There are very few examples of disorder related to the presence of a position shared by two different types of atom, like the description of the tripivaloylmethane 16 or a free neutral form of nicotine derivate. 17 In order to fix the problem, the rigid-body constraint AFIX 66 on the phenyl ring was used, generating the two phenyl rings from three assigned carbon atoms.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Racemic Triarylmethanol Derivative Crystallizes as a Chiral Crystal Structure with Enantiomeric Disorder, in the Sohncke Space Group P2₁

Chulvi

Costero

Ochando

et al. 2015

Crystal Growth & Design

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The X-ray crystal structure of a racemic triarylcarbinol derivate ((±)-1) was determined. Compound (±)-1 crystallizes as a chiral structure in the noncentrosymmetric Sohncke space group P2 1 and the crystals show a special case of enantiomeric disorder with two molecules of opposite handedness sharing many of the atomic positions in the asymmetric unit. The corresponding (R)-and (S)-enantiomers of 1 were separated by chiral HPLC, and crystallized independently yielding single crystals of both of them. The X-ray diffraction analysis of the crystals allowed the determination of the absolute configuration of both enantiomers (R)-1 and (S)-1. Both enantiomers establish intermolecular hydrogen bonds in the solid state, which induce significant differences in their molecular arrangement when compared to racemic crystal (±)-1. ■ INTRODUCTIONRacemic mixtures of chiral molecules can crystallize as racemic compounds (the most common situation, a single crystalline phase with both enantiomers in a 1:1 ratio in the elementary cell), as conglomerates of chiral crystals (mechanical mixture of enantiomerically pure crystals; about 10% of the time), or as pseudoracemates (or racemic solid solutions). Racemic compounds can yield either chiral or achiral crystal structures, and can theoretically be arranged in any one of the 230 space groups, 1 although around 95% of the known racemic compounds crystallize as centrosymmetric achiral crystal structures. 2 In this paper, we report the structural study of (4-(dimethylamino)phenyl)(phenyl)(thiophen-2-yl)methanol (1, see Figure 1), a chiral molecule which was synthesized as a racemic mixture from achiral precursors in the course of ongoing research. This compound was designed by our group to be used as an OFF/ON optical chemodosimeter for nerve agent mimics, due to the changes in its optical properties in the presence of these toxic compounds. 3 We have found that (±)-1 crystallizes as an ordered racemic crystal structure in the noncentrosymmetric space group P2 1 . This space group is one of 65 Sohncke space groups, which are the groups allowed for chiral crystal structures, containing only symmetry operations of the first kind (rotations and translations). 4 Actually, around of 5.2% of the CSD structures (of a total of 682 999) belong to a P2 1 space group. 5 Racemic mixtures that happen to crystallize as chiral crystal structures in Sohncke space groups are a very unusual case, and few examples have been reported in the literature. 6−9 Furthermore, the corresponding R and S enantiomers of 1 were separated by chiral HPLC, and crystallized independently yielding single crystals of both of them suitable for X-ray diffraction.■ EXPERIMENTAL SECTION X-ray Diffraction Analysis. Appropriate colorless acicular crystals of compound (±)-1 3 were grown from heptane/2-propanol as solvent at 4°C by means of liquid−liquid diffusion and analyzed by X-ray diffraction technique. The crystallization of the enantiomers, (S)-1 (1a) and (R)-1 (1b), was carried out at 4°C by the slow evaporation method...

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“…The preparation and crystallization of (I) were described in a previous publication (Kaitner & Stilinović, 2007). In the absence of significant resonant scattering, the Flack (1983) parameter was indeterminate; hence, the Friedel equivalent reflections were averaged.…”

Section: Methodsmentioning

confidence: 99%

“…In a previous publication (Kaitner & Stilinović, 2007) we reported the structure of tripivaloylmethane, (I), at room temperature. The three carbonyl groups of the triketo group define a helix, rendering the molecular conformation chiral.…”

Section: Commentmentioning

confidence: 99%

Partial ordering of tripivaloylmethane at 110 K

Stilinović¹,

Kaitner²

2008

Acta Crystallogr C

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Tripivaloylmethane [systematic name: 4-(2,2-dimethylpropanoyl)-2,2,6,6-tetramethylheptane-3,5-dione], C(16)H(28)O(3), is known to crystallize at room temperature in the space group R3m with three molecules in the unit cell. The molecules are conformationally chiral and pack so that each molecular site is occupied with equal probability by the two enantiomers. Upon cooling to 110 K, the structure partially orders; two molecules in the unit cell order into two different conformations of opposite chirality, while the third remains disordered. The symmetry of the resulting crystal is P3, with each of the molecules lying about a different threefold rotation axis. This paper describes an unusual case of order-disorder phase transition in which the structure partially orders by changes of molecular conformation in the single crystals. Such behaviour is of interest in the study of phase transitions and molecular motion in the solid state.

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Conformational enantiomeric disorder in tripivaloylmethane

Cited by 5 publications

References 8 publications

Observation of an infrequent enantiomer/conformer substitutional disorder in ethyl 13-ethyl-4-oxo-8,13-dihydro-4H-benzo[5,6]azepino[3,2,1-ij]quinoline-5-carboxylate heptane hemisolvate

Observation of an infrequent enantiomer/conformer substitutional disorder in ethyl 13-ethyl-4-oxo-8,13-dihydro-4H-benzo[5,6]azepino[3,2,1-ij]quinoline-5-carboxylate heptane hemisolvate

Racemic Triarylmethanol Derivative Crystallizes as a Chiral Crystal Structure with Enantiomeric Disorder, in the Sohncke Space Group P2₁

Partial ordering of tripivaloylmethane at 110 K

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Conformational enantiomeric disorder in tripivaloylmethane

Cited by 5 publications

References 8 publications

Observation of an infrequent enantiomer/conformer substitutional disorder in ethyl 13-ethyl-4-oxo-8,13-dihydro-4H-benzo[5,6]azepino[3,2,1-ij]quinoline-5-carboxylate heptane hemisolvate

Observation of an infrequent enantiomer/conformer substitutional disorder in ethyl 13-ethyl-4-oxo-8,13-dihydro-4H-benzo[5,6]azepino[3,2,1-ij]quinoline-5-carboxylate heptane hemisolvate

Racemic Triarylmethanol Derivative Crystallizes as a Chiral Crystal Structure with Enantiomeric Disorder, in the Sohncke Space Group P21

Partial ordering of tripivaloylmethane at 110 K

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Racemic Triarylmethanol Derivative Crystallizes as a Chiral Crystal Structure with Enantiomeric Disorder, in the Sohncke Space Group P2₁