The crystal structure of hydrate racemic acid

Abstract

cf. C.A. 44, 2818h. Racemic acid, one of the optically inactive forms of tartaric acid, forms triclinic crystals with parameters a = 8.06; b = 9.60; c = 4.85 A.; a = 70.4°; b = 97.2°; g = 112.5°. The measured sp. gr. is 1.700 ± 0.003, so that the unit cell contains one mol. of l-C4H6O6.d-C4H6O6.2H2O. Atomic parameters were obtained and refined by 2-dimensional electron d. summations. Some phase relations obtained from Harker-Kasper inequalities helped to det. the z parameters. The configuration of the tartaric acid mol. agrees with that found in Rochelle salt and in tartaric acid. The structure is held together by an extensive arrangement of H-bonds, all of which form closed systems. Columns are formed parallel to the c axis by square H-bond systems involving the OH groups. H-bonds between carboxyl groups hold these columns together in sheets parallel to (110), and these sheets are held together by water mols. Difficulties arise in the precise location of these H-bonds to the H2O mols. owing to the close approach of many O atoms. A plane arrangement is favored, although other possibilities exist.