Crystal structures tartaric acid

Louis Pasteur deduced in 1848 that the handedness of molecular structure is responsible for optical activity. He sorted the chiral crystals of tartaric acid salts into left-handed and right-handed forms, and discovered that the solutions showed equal and opposite optical activity. 

Pasteur s crystals of tartaric acid are more complex because the molecules contain two chiral carbon atoms. These can cancel out internally in the molecule so that three molecular forms actually exist, the two optically active mirror image structures that cannot be superimposed on each other, as the laevorota-tory (/-) and dextrorotatory (d-) forms, and the... 

The analysis of the Cambridge Structural Database [24] revealed many other examples of this pattern in the crystals of tartaric acid salts [25,26,27,28,30,31,32] and esters [29] as well as in the crystals of other hydroxyacids [33,34,35,36]. 

Although Pasteur was unable to provide a structural explanation—that had to wait for van t Hoff and Le Bel a quarter of a century later—he correctly deduced that the enantiomeric quality of the crystals was the result of enantiomeric molecules The rare form of tartanc acid was optically inactive because it contained equal amounts of (+) tartaric acid and (—) tartaric acid It had earlier been called racemic acid (from Latin racemus meaning a bunch of grapes ) a name that subsequently gave rise to our pres ent term for an equal mixture of enantiomers... 

Reagent 7 is easily prepared from commercially available diacetone-D-glucose and trichloro(cyclopentadienyl)titanium35 (Section 1.3.3.3.8.1.). The monomeric structure of reagent 7 was confirmed by an X-ray crystal structure analysis1 7. Complex 9 is obtained36 analogously from (7 .7 )-tartaric acid derived (R,7 )-2,3-CMsopropylidene-l,l,4,4-tetraphenyl-1,2,3,4-butanetetrol. 

Small molecule crystallographers are familiar with these concepts, since it is routine to measure data at low temperature to improve precision by reduction of thermal motion, and structures are often done at multiple temperatures to assess the origins of disorder in atomic positions. Albertsson et al. (1979) have reported the analysis of the crystal structure of Z)(-l-)-tartaric acid at 295, 160, 105, and 35 K. Figure 22 shows the individual isotropic. S-factors for the atoms in the structure at each of these temperatures the smooth variation of B with T is apparent. Below 105 K, B is essentially identical for all atoms and is also temperature independent the value of B = 0.7 agrees well with the expected zero-point vibradonal value. However, even for this simple structure, not all of the atoms show B vs T behavior at high temperature which extrapolates to 0 A at 0 K. 

Munoz-Guerra also studied stereoregular polyamides fully based on d- and L-tartaric acid [73]. The bispentachlorophenyl esters of both 2,3-di-(9-methyl-tartaric acids (22 and 23) were condensed with (2S, 3S )-2,3-dimethoxy-l,4-butanediamine (41) to obtain optically active (PTA-LL) and racemic (PTA-LD) polytartaramides. Fiber-oriented and powder X-ray studies of these polyamides demonstrated that PTA-LL crystallized in an orthorhombic lattice, whereas PTA-LD seemed to adopt a tricUnic structure. In both cases, the polymeric chain appears to be in a folded conformation more contracted than in the common y form of conventional nylons. 

Later, Pasteur 15) had arrived at the general stereochemical criterion for a chiral or dissymmetric molecular structure. Thus, the specific rotations of the two sets of sodium ammonium tartrate crystals in solution, isolated from the racemic mixture by hand-picking, were equal in magnitude and opposite in sign, from which Pasteur inferred that enantiomorphism of the dextro- and laevorotatory crystals is reproduced in the microscopic stereochemistry of the (+)- and (—)-tartaric acid molecules. The term dissymmetry or chirality is used when there is no superimposability between the two enantiomers, as seen in Sect. 2.1. 

Computational efforts to describe the conformational preferences of (R,R)-tartaric acid and its derivatives - mainly for isolated molecules - were made recently [18-25]. The conformations of these molecules also attracted attention from experimental chemists [22-40]. (/ ,/ [-tartaric acid and its dimethyl diester were observed in crystals, in conformations with extended carbon chain and planar a-hydroxy-carboxylic moieties (T.v.v and Tas for the acid and the ester, respectively) [25-28] (see Figure 2). The predominance ofthe T-structure was also shown by studies of optical rotation [31], vibrational circular dichroism (VCD) [23], Raman optical activity [32, 35], and nuclear magnetic resonance (NMR) [22, 33, 34]. The results of ab-initio and semiempirical calculations indicated that for the isolated molecules the Tsv and T as conformers were those of lowest energy [22, 21, 23, 25]. It should be noted, however, that early interpretations of NMR and VCD studies indicated that for the dimethyl diester of (/ ,/ [-tartaric acid the G+ conformation is favored [36-38]. 

In the case of tertiary amides, the planar arrangement of a-hydroxy-amide moieties is not favored due to bulky substituents. The repulsion between the N-alkyl substituents and the hydrogen atom attached to the distal Csp3 atom destabilizes the T structures of tertiary amides of (R,R [-tartaric acid [18,21,22]. As a result, the N,N,N ,N -tetramethyldiamide of (R,R [-tartaric acid is found in crystals in the G-p+p+ conformation, in which the main carbon chain is bent and the... 

The lowest-energy conformer in water solution of (R,R (-tartaric acid diamide - the Taa one (see Figure 3b) - closely resembles the structure found in crystals (see Figure 3c) and in polar solvents. It is stabilized by hydrogen bonds, each closing a five-membered ring with NH as donor and proximal OH as acceptor. Moreover, this Taa structure is stabilized by the attraction of antiparallel local dipoles formed along C -H and distal C=0 bonds. 

Figure 3. Structures of (7 ,7 )-tartaric acid diamide (a) lowest-energy conformer for isolated molecule (b) lowest-energ conformer in aqueous solution (c) crystal structure Figs (a), (c) adapted from ref. 22. ...

Some of the first, and most versatile hosts are compounds 3a-c, which can be prepared from optically active tartaric acid. It has been found that they work as chiral selectors in solution [17], and in a powdered state [18], In the crystal structure of the free host compound (R,R)-(—)-fra s-bis(hydroxydiphenylmethyl)-l, 4-dioxaspiro[4.5]decane (3c), only one hydroxyl group is intramolecularly hydrogen bonded (Figure 1). As long as no suitable guest molecules are present, the other OH-group remains unbonded in both media. 

Kozma, D., Bocskei, Zs., Kassai, Cs., Simon, K., and Fogassy, E. Optical resolution of racemic alcohols by diastereoisomeric complex formation with 0,0 -dibenzoyl-(2R,3R)-tartaric acid, the crystal structure of the (-)-lR,2 S, 5R-menthol.O,0,-dibenzoyl-(2R,3R)-tartaric acid complex. J. Chem. Soc. Chem. Commun. 1996, 753-754. 

Ryhlewska, U., and Warzajtis, B. Interplay between dipolar, stacking and hydrogen-bond interactions in the crystal structures of unsymmetrically substituted esters, amides and nitriles of (R,R)-0,0 -dibenzoyltartaric acid, Acta Cryst., Sec. B. 2001, B57, 415-427. Isostructuralism in a series of methyl ester/methylamide derivatives of (R,R)-0,0 -dibenzoyl tartaric acid inclusion properties and guest-dependent homeotypism of the crystals of (2R,3R)-0,0 -dibenzoyltartaric acid diamide, Acta Cryst., Sec. B. 2002,B58, 265-271. 

Kovari, Z., Bocskei, Zs., Kassai, Cs., Fogassy, E., and Kozma, D. Investigation of the structural background of stereo- and enantioselectivity of 0,0 -dibenzoyl-(2/ ,3R)-tartaric acid-alcohol supramolecular compound formation, Chirality 2003, submitted for publication. Crystal data are deposited at the Cambridge Crystal Structure Data Base under the following numbers CCDC 181497, 181498, 181499,181500, 181501, 181502, 181503, 181504,181505. 

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