Existence of sets of two or more substances with identical molecular formulas (see chemical formula ) but different configuration s and hence different properties.
bonding differs. For example, C 2 H 6 O is the molecular formula for both ethanol (CH 3 CH 2 OH) and methyl {{link=ether">ether (CH 3 OCH 3 ). Constitutional isomers that can be readily converted from one to another are called tautomers (see tautomerism ). In stereoisomerism, substances with the same atoms are bonded in the same ways but differ in their three-dimensional configurations. See also isomer .