L-isomer

An L-isomer is a term used in stereochemistry to describe a chemical that has a non superimposable mirror image counterpart. An atom that has four different groups attached to it and gives rise to this phenomenon is called the chiral centre or more commonly the chiral carbon. The L stands for levorotary and the D dextrorotary which references their ability to change light polarization.

Isomers are incredibly important in Biochemistry. An often cited example is the Thalidomide disaster in the 1960s. Thalidomide was used as a anti-sickness medicine in pregnancy however the drug given involved a racemic mixture, one of the isomers was poisonous to unborn foetuses and babies were born with congenital birth defects. The mechanisms of actions are still unknown and debated with over 30 different hypothesis proposed on how thalidomide affects humans and subsequent animal models.