CHEM 121 glossary
Isomer
Compounds with the same molecular formula but different structures. Because properties come from structure, isomers can differ greatly in boiling point, reactivity and biological effect.
2-Methylpropane, a branched isomer of butane ().
Example
Butane boils at −0.5 °C, but its branched isomer 2-methylpropane boils at −11.7 °C: the compact shape gives less contact and weaker dispersion forces.