Alpha carbon

Alpha Carbon

The alpha carbon (α-carbon) is a term used in organic chemistry to describe the first carbon atom that is attached to a functional group, such as a carbonyl group, in a molecule. It is a key concept in understanding the structure and reactivity of organic compounds, particularly in the context of amino acids, carbonyl chemistry, and stereochemistry.

Structure

In a typical organic molecule, the alpha carbon is the carbon atom directly bonded to a functional group. For example, in a carbonyl compound, the alpha carbon is the carbon atom adjacent to the carbonyl carbon. In amino acids, the alpha carbon is the central carbon atom to which the amino group, carboxyl group, and side chain (R group) are attached.

Importance in Amino Acids

In the context of amino acids, the alpha carbon is of particular importance because it is the chiral center in all amino acids except glycine. This chirality is crucial for the structure and function of proteins, as it determines the three-dimensional arrangement of the amino acids in a polypeptide chain.

Reactivity

The alpha carbon is often a site of reactivity in organic molecules. For example, in carbonyl chemistry, the hydrogen atoms attached to the alpha carbon (known as alpha hydrogens) are slightly acidic and can be deprotonated to form an enolate ion. This enolate ion can then participate in various reactions, such as the Aldol reaction and Claisen condensation.

Stereochemistry

The configuration of the alpha carbon in amino acids is described using the Cahn-Ingold-Prelog priority rules, which assign an R or S configuration. This stereochemistry is critical in determining the properties and biological activity of amino acids and proteins.

Also see

• Amino acid
• Chirality (chemistry)
• Carbonyl group
• Enolate ion
• Stereochemistry