Editing Stereochemistry (section)

==Significance==
[[Cahn–Ingold–Prelog priority rules]] are part of a system for describing a molecule's stereochemistry. They rank the atoms around a stereocenter in a standard way, allowing unambiguous descriptions of their relative positions in the molecule. A [[Fischer projection]] is a simplified way to depict the stereochemistry around a stereocenter.

===Thalidomide example===
[[Image:Thalidomide enantiomers.svg|class=skin-invert-image|upright=0.56|thumb|Enantiomers of thalidomide]]
Stereochemistry has important applications in the field of medicine, particularly pharmaceuticals. An often cited example of the importance of stereochemistry relates to the thalidomide disaster. [[Thalidomide]] is a [[pharmaceutical drug]], first prepared in 1957 in Germany,  prescribed for treating morning sickness in pregnant women. The drug was discovered to be [[Teratology|teratogenic]], causing serious [[genetics|genetic]] damage to early embryonic growth and development, leading to limb deformation in babies. Several proposed [[Thalidomide#Teratogenic mechanism|mechanisms]] of teratogenicity involve different biological functions for the (R)- and (S)-thalidomide enantiomers.<ref name="Stephens">{{cite journal
|vauthors=Stephens TD, Bunde CJ, Fillmore BJ | title = Mechanism of action in thalidomide teratogenesis
| journal = [[Biochemical Pharmacology (journal)|Biochemical Pharmacology]]
| volume = 59
| issue = 12
| pages = 1489–99
|date=June 2000
| pmid = 10799645
| doi = 10.1016/S0006-2952(99)00388-3
}}</ref> In the human body, however, thalidomide undergoes [[racemization]]: even if only one of the two enantiomers is administered as a drug, the other enantiomer is produced as a result of metabolism.<ref>{{cite journal |journal= Clin. Pharmacokinet. |year= 2004 |volume= 43 |issue= 5 |pages= 311–327 |title= Clinical pharmacokinetics of thalidomide |pmid= 15080764 |vauthors=Teo SK, Colburn WA, Tracewell WG, Kook KA, Stirling DI, Jaworsky MS, Scheffler MA, Thomas SD, Laskin OL |doi= 10.2165/00003088-200443050-00004 |s2cid= 37728304 }}</ref> Accordingly, it is incorrect to state that one stereoisomer is safe while the other is teratogenic.<ref name="chemicalmyth">{{cite journal | title=Urban legends of chemistry | author=Francl, Michelle | journal=Nature Chemistry | year=2010 | volume=2 | issue=8 | pages=600–601 | doi=10.1038/nchem.750 | pmid=20651711 | bibcode=2010NatCh...2..600F }}</ref> Thalidomide is currently used for the treatment of other diseases, notably cancer and [[leprosy]]. Strict regulations and controls have been implemented to avoid its use by pregnant women and prevent developmental deformities. This disaster was a driving force behind requiring strict testing of drugs before making them available to the public.

In yet another example, the drug [[ibuprofen]] can exist as (R)- and (S)-isomers. Only the (S)-ibuprofen is active in reducing inflammation and pain.<ref>{{Cite journal |last1=Geisslinger |first1=G. |last2=Stock |first2=K. -P. |last3=Bach |first3=G. L. |last4=Loew |first4=D. |last5=Brune |first5=K. |date=June 1989 |title=Pharmacological differences between R(−)-and S(+)-ibuprofen |url=http://link.springer.com/10.1007/BF01972851 |journal=Agents and Actions |language=en |volume=27 |issue=3–4 |pages=455–457 |doi=10.1007/BF01972851 |pmid=2801337 |issn=0065-4299}}</ref><ref>{{Cite journal |last=Evans |first=A. M. |date=November 2001 |title=Comparative Pharmacology of S(+)-Ibuprofen and (RS)-Ibuprofen |url=http://link.springer.com/10.1007/BF03342662 |journal=Clinical Rheumatology |language=en |volume=20 |issue=S1 |pages=9–14 |doi=10.1007/BF03342662 |pmid=11771573 |issn=0770-3198}}</ref>