Discrimination in resolving systems. II: Ephedrine-substituted mandelic acids

Chirality
E J ValenteX Shui

Abstract

Binary diastereomeric (-) (1R,2S)-ephedrine salts of various mandelic acids obtained from 95% ethanol show considerable differences in solubility. Structures and some properties of the less-soluble (L) and more-soluble (M) solid phases of (-)-ephedrine with unsubstituted mandelic acid, 2-, 3-, and 4-monosubstituted halo (F, Cl, Br) mandelic acids, and 3- and 4-methylmandelic acids have been determined. Salts were found to be binary, without solvent of crystallization, and composed of double-layered arrays of alternating anions and cations linked by H-bonds normal to the layers. H-bonding links charged donors and acceptors usually along a crystallographic 2-fold screw axis. A striking discrimination is evident in that the (2R)-mandelate salts typically display a compact four-atom chain as the H-bonding repeating unit [+N--H...O(-C(-)--O)...H-N', C2(1)(4)] while the (2S)-mandelate salts adopt a more dimensionally variable six-atom chain repeating unit [+N--H...O--C(-)--O...H--N', C2(2)(6)]. Two distinct packing schemes display the shorter H-bonding chain of the (2R)-mandelates which always occurs with ephedrinium ions in the fully extended conformation. Slightly greater packing efficiency and H-bonding energies of the (2R)-mandel...Continue Reading

References

Jan 1, 1992·Chirality·E J ValenteD S Eggleston
Dec 30, 1991·Carbohydrate Research·G A Jeffrey, D B Huang
Apr 1, 1990·Acta Crystallographica. Section B, Structural Science·M C EtterJ Bernstein
Mar 20, 1987·Science·J Rebek

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