Editing Racemic mixture (section)

==Crystallization==
There are four ways to crystallize a racemate; three of which [[Hendrik Willem Bakhuis Roozeboom|H. W. B. Roozeboom]] had distinguished by 1899:

;Conglomerate (sometimes ''racemic conglomerate''):If the molecules of the substance have a much greater affinity for the same enantiomer than for the opposite one, a mechanical mixture of enantiomerically pure crystals will result. The mixture of enantiomerically pure R and S crystals forms a [[Eutectic system|eutectic]] mixture. Consequently, the [[melting point]] of the conglomerate is always lower than that of the pure enantiomer. Addition of a small amount of one enantiomer to the conglomerate increases the melting point. Roughly 10% of racemic chiral compounds crystallize as conglomerates.<ref>{{cite book |last1=Jacques |first1=Jean |last2=Collet |first2=André |last3=Wilen |first3=Samuel H. |title=Enantiomers, racemates, and resolutions |date=1981 |publisher=Wiley |isbn=978-0-471-08058-9 |oclc=7174200 }}{{page needed|date=July 2022}}</ref>
;Racemic compound (sometimes ''true racemate''):If molecules have a greater affinity for the opposite [[enantiomer]] than for the same enantiomer, the substance forms a single crystalline phase in which the two enantiomers are present in an ordered 1:1 ratio in the elementary cell. Adding a small amount of one enantiomer to the racemic compound decreases the melting point. But the pure enantiomer can have a higher or lower melting point than the compound. A special case of racemic compounds are [[kryptoracemic compounds]] (or [[Kryptoracemic compounds|kryptoracemates]]), in which the crystal itself has handedness (is enantiomorphic), despite containing both enantiomorphs in a 1:1 ratio.<ref>{{cite journal |last1=Fábián |first1=László |last2=Brock |first2=Carolyn Pratt |title=A list of organic kryptoracemates |journal=Acta Crystallographica Section B: Structural Science |date=1 February 2010 |volume=66 |issue=1 |pages=94–103 |doi=10.1107/S0108768109053610 |pmid=20101089 }}</ref>
;Pseudoracemate (sometimes ''racemic solid solution''): When there is no big difference in affinity between the same and opposite enantiomers, then in contrast to the racemic compound and the conglomerate, the two enantiomers will coexist in an unordered manner in the crystal lattice. Addition of a small amount of one enantiomer changes the melting point slightly or not at all.
;Quasiracemate: A quasiracemate is a co-crystal of two similar but distinct compounds, one of which is left-handed and the other right-handed. Although chemically different, they are sterically similar (isosteric) and are still able to form a racemic crystalline phase. One of the first such racemates studied, by Pasteur in 1853, forms from a 1:2 mixture of the bis [[ammonium salt]] of (+)-[[tartaric acid]] and the bis ammonium salt of (−)-[[malic acid]] in water. Re-investigated in 2008,<ref>{{cite journal |last1=Wheeler |first1=Kraig A. |last2=Grove |first2=Rebecca C. |last3=Davis |first3=Raymond E. |last4=Kassel |first4=W. Scott |title=Rediscovering Pasteur's Quasiracemates |journal=Angewandte Chemie International Edition |date=January 2008 |volume=47 |issue=1 |pages=78–81 |doi=10.1002/anie.200704007 |pmid=18022885 }}</ref> the crystals formed are [[dumbbell]]-shape with the central part consisting of ammonium (+)-bitartrate, whereas the outer parts are a quasiracemic mixture of ammonium (+)-bitartrate and ammonium (−)-bimalate.