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A '''chiral molecule''' is a molecule that cannot be superimposed on its mirror image.  Chiral molecules are optically active in the sense that they rotate the plane of polarized light.

A '''chiral molecule''' is a molecule that cannot be superimposed on its mirror image.  Chiral molecules are optically active in the sense that they rotate the plane of [[polarized light]].

==Louis Pasteur==

==Louis Pasteur==

[[Louis Pasteur]] encountered the phenomenon of optical activity in 1843, during his investigation of the crystalline sediment that accumulated in wine casks (a form of tataric acid called paratartaric acid - also called racemic acid, from the Latin racemus, "bunch of grapes").  He used fine forceps to separate two types of crystals identical in shape but mirror images of each other in structure.  Both types proved to have all the chemical properties of tartaric acid, but in solution one type rotated plane-polarized light to the left (levorotatory), the other to the right (dextrorotatory).  Pasteur later described the experiment and its interpretation:

[[Louis Pasteur]] encountered the phenomenon of optical activity in 1843, during his investigation of the crystalline sediment that accumulated in wine casks (a form of [[tataric acid]] called paratartaric acid - also called racemic acid, from the Latin racemus, "bunch of grapes").  He used fine forceps to separate two types of crystals identical in shape but mirror images of each other in structure.  Both types proved to have all the chemical properties of tartaric acid, but in solution one type rotated plane-polarized light to the left (levorotatory), the other to the right (dextrorotatory).  Pasteur later described the experiment and its interpretation:

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