Isomerism
The existence of two or more compounds with the same molecular formula but different arrangements of atoms.
Unit
Dimensionless
In depth
Isomerism divides into structural, where the connectivity differs, and stereoisomerism, where connectivity is identical but the three-dimensional arrangement differs. The number of possible isomers grows explosively with molecular size, which is a major reason organic compounds are so numerous.
Examples in the real world
C₄H₁₀ has two isomers; C₁₀H₂₂ has 75; C₃₀H₆₂ has more than four billion.