Define optical isomers and provide an example.

Optical isomers are molecules that have the same chemical formula but differ in their spatial arrangement.

Optical isomers, also known as enantiomers, are a type of stereoisomer. They have the same chemical formula and functional groups, but differ in the way that their atoms are arranged in space. This leads to differences in their physical and chemical properties, such as their melting and boiling points, solubility, and reactivity.

One example of optical isomers is the amino acid alanine. Alanine has a chiral carbon atom, which means that it has four different groups attached to it. This results in two possible arrangements of the molecule, which are mirror images of each other. These two forms of alanine are known as L-alanine and D-alanine. They have the same chemical formula and properties, but they rotate plane-polarized light in opposite directions.

Optical isomers are important in many biological processes, such as enzyme-catalysed reactions and the recognition of molecules by receptors in the body. They are also used in the production of pharmaceuticals, where the different properties of the isomers can have a significant impact on their effectiveness and safety.