Stereocenter

Stereocenter

A stereocenter (or stereogenic center) is an atom in a molecule that is the site of stereoisomerism. It is a point in a molecule where the interchange of two groups produces a stereoisomer. Stereocenters are critical in the study of stereochemistry, which is the branch of chemistry concerned with the three-dimensional arrangement of atoms in molecules.

Definition

A stereocenter is typically a carbon atom bonded to four different substituents, leading to chirality. However, stereocenters can also be other atoms, such as nitrogen or phosphorus, provided they have the appropriate substituents to create stereoisomerism.

Types of Stereocenters

Chiral Centers

A chiral center is a type of stereocenter where the atom is bonded to four different groups, resulting in non-superimposable mirror images, known as enantiomers. The presence of a chiral center in a molecule is a common cause of chirality.

Double Bond Stereocenters

In addition to chiral centers, stereocenters can also occur at double bonds. In such cases, the stereochemistry is described using the terms "cis" and "trans" or "E" and "Z" to denote the relative positions of substituents around the double bond.

Importance in Chemistry

Stereocenters are crucial in the field of pharmaceutical chemistry because the different stereoisomers of a compound can have vastly different biological activities. For example, one enantiomer of a drug may be therapeutically beneficial, while the other may be inactive or even harmful.

Determination of Stereochemistry

The configuration of a stereocenter is determined using the Cahn-Ingold-Prelog priority rules, which assign priorities to substituents based on atomic number and connectivity. The stereochemistry is then described as "R" (rectus) or "S" (sinister) for chiral centers, and "E" (entgegen) or "Z" (zusammen) for double bond stereocenters.

Examples

- Lactic Acid: Lactic acid has a chiral center at the carbon atom bonded to the hydroxyl group, methyl group, and carboxyl group, leading to two enantiomers: L-lactic acid and D-lactic acid. - Ibuprofen: This common nonsteroidal anti-inflammatory drug (NSAID) has a chiral center, and its S-enantiomer is the active form.

Also see

• Chirality (chemistry)
• Enantiomer
• Diastereomer
• Cahn-Ingold-Prelog priority rules
• Stereochemistry