Isomer

Name:
Isomer
Detailed information:
(1) One of two or more molecules having the same number and kind of atoms and hence the same molecular weight, but differing in respect to the arrangement or configuration of the atoms. Butanol (C₄H₉OH or C₄H₁₀O) and ethyl ether (C₂H₅OC₂H₅ or C₄H₁₀O) have the same empirical formulas but are entirely different kinds of substances; normal butanol (CH₃CH₂CH₂CH₂OH) and isobutanol ([CH₃]₂CHCH₂OH) are the same kinds of substances, differing chiefly in the shape of the molecules; sec-butanol (CH₃CH₂OCH₂CH₃) exists in two forms, one a mirror image of the other (enantiomer). Isomers often result from location of an atom or group of a compound at various positions on a benzene ring, e.g., xylene, dichlorobenzene.(2) Nuclides (i.e. kinds of atomic nuclei) having the same atomic and mass numbers, but existing in different energy states. One is always unstable with respect to the other, or both may be unstable with respect to a third. In the latter instance the energy of transformation in the two cases will differ.See Geometric Isomer; Optical Isomer.