3-Hydroximino-isoindolines and 3-hydroxylamino-1 H-isoindoles with substituents at the five membered ring have been prepared by condensation of substituted 3-alkoxy-1 H-isoindoles with hydroxylamine and O-/N -substituted hydroxylamines. Constitution and configuration of semi-cyclic amidoximes were derived from spectroscopic investigations and deduced on the basis of orientating chemical transformations. These results have been established by a crystal structure determination of a representative 3-hydroximino-isoindoline.