Abstract
Reasons are given for the belief that many new chemical reactions may be obtained in the excited electronic states of the molecules. By the examples of nitrobenzene, trans → cis isomerization of stilbene and azobenzene, by an interpretation of experimental results concerning acidity and basicity of certain bodies in the excited states, and the evaluation of the charges and dipole moments of the C==N group in different excited states, it is shown how the chemical and physicochemical properties of the molecule may vary from one state to another.