Friday, September 12, 2008

Chiral Molecules - July Dec Revision

Chiral molecules

A molecule is said to be chiral if it lacks symmetry and its mirror images are not superimposable. To be chiral a molecule must lack symmetry, that is, a chiral molecule can not have any type or symmetry.

Carbon atoms with four sp3 hybridized orbitals can enter into up to four different bonds about the central carbon atom.
When the central carbon bonds with differing atoms or groups of atoms the carbon is termed an asymmetric carbon atom.

Bromochlorofluoromethane is an example of such a molecule. The central carbon, with four sp3 bonds oriented (pointing) to the corners of a tetrahedron, is bonded to a bromine, chlorine, fluorine and methane atoms. There is no symmetry to this molecule.

To explain things in a more simple way, Chiral molecules are like right hand left hand. Both hands have identical fingers but in different orientations. The little finger is in clockwise direction from the middle finger in right hand, where as the little is in the counterclockwise direction in the left hand. So you can fix a right hand to another person's left wrist. Right hand and left hand are different even though all the five diffetent fingers are more or less similar in both the hands.

Enantiomers are optical isomers. A chiral molecule will have enantiomers.

A solution in which both enantiomers of a compound are present in equal amounts is called a racemic mixture, or racemate.

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