The property of compounds (isomers) which have the same molecular formula but different physical and chemical properties. The difference in properties is caused by a difference in molecular structure (that is, molecular architecture). A typi­cal example is dimethyl ether, CH₃OCH₃, a chemi­cally quite inert gas which condenses at −24°C (−11°F), and ethyl alcohol, CH₃CH₂OH, a liquid of substantial chemical reactivity which boils at 78°C (172°F); both compounds have the molecular formula C₂H₆O.