Lstereoisomer

Lstereoisomer is a term used in stereochemistry to denote one member of a pair of stereoisomers that are related by reflection, specifically an enantiomer that has the same connectivity as another molecule but a different spatial arrangement. The prefix L indicates the configuration of the molecule relative to L-glyceraldehyde, the reference compound used in the classical D/L (or D-L) naming system. In Fischer projections, the L form corresponds to the left-hand configuration at the stereocenter that is analogous to glyceraldehyde.

In practice, the L designation is most familiar in biochemistry: most naturally occurring amino acids found in proteins are in the L-configuration. By contrast, the D- configuration is more common for many sugars. The D/L system is a historical convention based on comparison to glyceraldehyde and is orthogonal to the modern R/S (Cahn–Ingold–Prelog) absolute configuration system. Importantly, the D/L label does not directly indicate optical rotation; a molecule can be dextrorotatory or levorotatory regardless of being D or L.

A single pair of enantiomers consists of an L-stereoisomer and an corresponding D-stereoisomer. The concept is central to understanding chirality in organic molecules, including amino acids, sugars, and many pharmaceuticals. The term L-stereoisomer is more common in discussions of configuration relative to glyceraldehyde, whereas modern naming often emphasizes absolute configuration or uses the D/L descriptor as historical shorthand.