This chapter continues the exploration of stereochemistry in organic compounds,
focusing on detailed methods for describing and differentiating the spatial arrangement of atoms
within molecules. It begins with absolute configuration, which provides a precise description of the
spatial arrangement of atoms around a chiral center, independent of other molecules.
Relative configuration is then discussed, explaining how the arrangement of atoms in one chiral
molecule relates to another, often determined through chemical interconversion. The D-L system, a
traditional method for denoting configurations based on the molecule’s relationship to
glyceraldehyde, is introduced for historical context and specific applications.
The R-S system, the modern and widely used method for assigning absolute configuration based on
the Cahn-Ingold-Prelog priority rules, is detailed, providing a systematic approach for designating
chiral centers. Geometrical isomerism is explored next, focusing on compounds with restricted
rotation around double bonds or ring structures, resulting in distinct cis-trans configurations.
The E-Z system, an advanced method for designating geometrical isomers based on the CahnIngold-Prelog priority rules, is introduced, offering a more precise description for complex
molecules. Conformational isomerism, which arises from the rotation around single bonds, is then
examined, highlighting its significance in the dynamic behavior of molecules.
Various conformations, particularly those of cycloalkanes and acyclic compounds, are analyzed,
discussing the energy differences and interconversions between different conformers. Special
attention is given to the impact of conformational isomerism on chemical reactivity and physical
properties.
This chapter provides a deep understanding of the nomenclature and principles used to describe the
three-dimensional arrangements of atoms in organic molecules, building on the foundations laid in
the previous chapter. Mastery of these concepts prepares readers to analyze and predict the behavior
of complex organic systems, essential for advanced studies and practical applications in organic
chemistry.
Keywords: Absolute configuration; relative configuration; D-L system; R-S system; geometrical isomerism; E-Z system; conformational isomerism; conformations.
