Organic and Inorganic Chemistry Lesson of the Day – Racemic Mixtures
August 13, 2014 Leave a comment
A racemic mixture is a mixture that contains equal amounts of both enantiomers of a chiral molecule. (By amount, I mean the usual unit of quantity in chemistry – the mole. Of course, since enantiomers are isomers, their molar masses are equal, so a racemic mixture would contain equal masses of both enantiomers, too.)
In synthesizing enantiomers, if a set of reactants combine to form a racemic mixture, then the reactants are called non-stereoselective or non-stereospecific.
in 1895, Otto Wallach proposed that a racemic crystal is more dense than a crystal with purely one of the enantiomers; this is known as Wallach’s rule. Brock et al. (1991) substantiated this with crystallograhpic data.
Brock, C. P., Schweizer, W. B., & Dunitz, J. D. (1991). On the validity of Wallach’s rule: on the density and stability of racemic crystals compared with their chiral counterparts. Journal of the American Chemical Society, 113(26), 9811-9820.