In chemistry, isomerization is the transformation of a molecule into a different isomer. In some molecules and under some conditions, isomerization occurs spontaneously. Many isomers are equal or roughly equal in bond energy, and so interconvert relatively freely. Chemistry (in Greek: χημεία) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of bonds between atoms, but in which the atoms are arranged differently. ... In chemistry, bond energy (E) is a measure of bond strength in a chemical bond. ...
An isomer is a long-lived excited state of an atom's nucleus--a state in which decay back to the nuclear ground state is inhibited.
A nuclear isomer is an atom whose nucleus is in a higher energy state than its ground state.
The long lifetime results because transition to the ground state would require a large change either in the spatial structure of the atom's nucleus (for a shape isomer) or in the angular momentum (a measure of the spin of the nucleus) between the isomer and the nuclear ground state (for a spin isomer).
Isomers are classified as structural isomers, which have the same number of atoms of each element and molecular weight but different bonding patterns (see chemical bond), or as stereoisomers, which have the same number of atoms of each element, molecular weight, and bonding pattern but in which the atoms have different spatial relationships.
Tautomers are structural isomers that readily convert from one isomeric form to another and therefore exist in equilibrium.
Position isomers have similar chemical properties since they differ only in the location of the functional group (e.g., the OH in an alcohol or the double bond in an alkene).
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