Illustrated Glossary of Organic Chemistry

Relative configuration: The position of atoms or groups in space in relation to (i.e., relative to) something else in the molecule. Compare with absolute configuration, which is independent of atoms or groups elsewhere in the molecule.

Relative to the position of the methyl group, the chlorine atom is on the same face of the cyclohexane ring. The stereocenter bearing the chlorine atom has an R absolute configuration (this configuration does not involve or depend on positions elsewhere in the molecule). Hence this molecule is cis-1-chloro-2-methylcyclohexane or (1R, 2S)-1-chloro-2-methylcyclohexane.

In cis-2-pentene, the methyl and ethyl groups are on the same side of the alkene. The groups with highest Cahn-Ingold-Prelog priority are on the same face of the alkene, so this is also (Z)-2-pentene. In trans-2-pentene, also named (E)-2-pentene, the methyl and ethyl groups are on opposite faces of the alkene. Cis, trans, E, and Z are all designations of relative configuration.

At the stereocenter next to the CH2OH carbon, both of these monosaccharides have the OH group pointing to the right, so they have the same relative configuration. This relative configuration is indicated with the prefix D. D and L are designations of relative configuration.