Chiral center

A chiral center in chemistry is an atom within a molecule that has four different substituents attached to it, leading to molecular chirality. This configuration makes the molecule non-superimposable on its mirror image, much like left and right hands are mirror images but cannot be perfectly aligned on top of each other. The presence of a chiral center typically results in two different forms of the molecule, known as enantiomers. These enantiomers have identical physical properties except for their ability to rotate plane-polarized light in opposite directions, a property known as optical activity.

Structure and Identification

The central atom of a chiral center is usually a carbon atom, but it can also be a nitrogen, sulfur, or phosphorus atom. Each of these atoms must be bonded to four different groups or atoms. The spatial arrangement of these groups can be represented using three-dimensional molecular models or stereochemical drawings.

Significance in Biochemistry and Pharmacology

Chiral centers are crucial in the field of biochemistry, where the three-dimensional arrangement of atoms can determine the biological function of a molecule. Many biological molecules, including amino acids, sugars, and nucleic acids, are chiral. In pharmacology, the different enantiomers of a drug can have vastly different therapeutic effects, side effects, and metabolism. This has led to the development of chiral drugs, where the focus is on the synthesis and use of one specific enantiomer.

Chirality in Synthetic Chemistry

In synthetic chemistry, the creation of chiral centers is a significant challenge. Techniques such as asymmetric synthesis are employed to selectively produce the desired enantiomer. Catalysts, particularly those that are chiral themselves, are often used to influence the outcome of reactions that generate chiral centers.

Examples

A simple example of a molecule with a chiral center is lactic acid, which has two enantiomers: L-lactic acid and D-lactic acid. The chiral center in lactic acid is the carbon atom that is bonded to an OH group, a hydroxyl group, and a methyl group.

See Also

• Stereochemistry
• Enantiomer
• Optical isomerism
• Racemic mixture