Chiral compound

Chiral Compound

A chiral compound is a type of molecule that has a non-superimposable mirror image, much like how left and right hands are mirror images but cannot be perfectly aligned on top of each other. This property of chirality is a fundamental concept in stereochemistry, a branch of chemistry that studies the spatial arrangement of atoms in molecules.

Definition and Characteristics

A molecule is considered chiral if it lacks an internal plane of symmetry and has an enantiomer, which is a mirror image that cannot be superimposed onto the original molecule. The presence of an asymmetric carbon atom, also known as a chiral center, is a common cause of chirality in organic compounds. A chiral center is typically a carbon atom bonded to four different substituents.

Enantiomers

Enantiomers are pairs of chiral molecules that are mirror images of each other. They have identical physical properties, such as melting point and boiling point, but they often exhibit different chemical behaviors, especially in biological systems. This is due to the fact that many biological molecules are themselves chiral and can interact differently with each enantiomer.

Importance in Biology and Medicine

Chirality is of paramount importance in biochemistry and pharmacology. Many biological molecules, including amino acids and sugars, are chiral. The L-amino acids and D-sugars are the forms predominantly found in nature. In the field of medicine, the chirality of a drug can significantly affect its pharmacodynamics and pharmacokinetics. For example, one enantiomer of a drug may be therapeutically active, while the other may be inactive or even harmful.

Examples

• Thalidomide: A notorious example of chirality in medicine is thalidomide, which was used as a sedative and anti-nausea drug. One enantiomer was effective for its intended use, while the other caused severe birth defects.
• Ibuprofen: This common nonsteroidal anti-inflammatory drug (NSAID) is sold as a racemic mixture, but only one enantiomer is active in reducing inflammation.

Synthesis and Resolution

The synthesis of chiral compounds can be challenging due to the need to control the stereochemistry of the product. Several methods are used to achieve this, including:

• Chiral Pool Synthesis: Utilizing naturally occurring chiral molecules as starting materials.
• Asymmetric Synthesis: Employing chiral catalysts or reagents to induce chirality in the product.
• Resolution: Separating a racemic mixture into its individual enantiomers, often using chiral chromatography or crystallization techniques.

Analytical Techniques

Several analytical techniques are used to study chiral compounds, including:

• Polarimetry: Measures the rotation of plane-polarized light by a chiral compound.
• Chiral Chromatography: Separates enantiomers based on their interaction with a chiral stationary phase.
• NMR Spectroscopy: Can be used with chiral shift reagents to distinguish between enantiomers.

See Also

• Stereochemistry
• Enantiomer
• Racemic mixture
• Optical isomerism

External Links

• Chemistry World
• Royal Society of Chemistry