Stereoisomerism
Isomerism in which molecules have identical connectivity but differ in the spatial arrangement of their atoms.
Unit
Dimensionless
In depth
Stereoisomers cannot be interconverted without breaking a bond or, for conformers, without rotation. They are divided into geometric isomers, arising from restricted rotation, and optical isomers, arising from chirality. Their separation often requires specialised chiral techniques.
Examples in the real world
Cis and trans but-2-ene; the two mirror-image forms of lactic acid.