Chirality (Organic chemistry)
Organic chemistry > Stereochemistry > Chirality
Chirality (pronounced KIE-rail-it-tee) is the property of handedness. Any object can have this property, including molecules. An object that is chiral is an object that can not be superimposed on its mirror image. Chiral objects don't have a plane of symmetry. Achiral object have at least one.
Chiral Compounds With Stereocenters
If a carbon atom has 4 different substituents, that carbon atom is a stereocenter. A chiral molecules may have one or more stereocenters. When drawing molecules, stereocenters are usually indicated with an asterisk near the carbon. Chiral molecules are called enantiomers.
Example:
Left: The carbon atom has a Cl, a Br, and 2 CH3. That's only 3 different substituents, which means this is not a stereocenter.
Center: The carbon atom has one ethyl group (CH2CH3), one methyl group (CH3) and 2 H. This is not a stereocenter.
Right: The carbon atom has a Cl and 1 H. Then you must look around the ring. Since one side has a double bond and the other doesn't, it means the substituents off that carbon are different. The 4 different substituents make this carbon a stereocenter and makes the molecule chiral.
Chiral Compounds Without Stereocenters
Some compounds have chirality but with no stereocenters.
For example, the isomers which is shown by the following figure are different. The two isomers cannot convert from one to another spontaneously because of restriction of rotation of double bonds.
Other types of chiral compounds without stereocenters (like restriction of rotation of a single bond because of steric hindrance) also exist.
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