Studies in cyclic nitroxide radicals

Abstract

INTRODUCTION Interest in the chemistry of nitroxide radicals has intensified over the past twenty years resulting in an expo nential growth in the study of nitroxides from several varied standpoints. These include the intrinsic theoretical, spectroscopic, chemical aspects and the broader application to allied sciences such as molecular biology, biophysics and polymer chemistry. Several reviews on nitroxide radical chemistry have been published and these serve to indicate the great divers ity of structural types into which the nitroxide nucleus has been embedded. The principal objective of this introduction is, however, to highlight the progress made in aliphatic nitroxide radical chemistry. Attention will be focused on the electronic and spectroscopic properties of this class of nitroxide. An attempt will also be made to describe the various synthetic methods which have been applied to prepare them. The first nitroxide radical reported was made in 18^5 by Fremy° who prepared the inorganic salt (l), but the first organic nitroxide, porphyrexide (2), was synthesised at the 7 beginning of this century by Piloty and Schiverin . Many years passed before a number of relatively stable diaryl 1 2 . 8 nitroNides of the type (3)> R and R = aryl, were obtained . However, it was not until 1959 that the first completely aliphatic nitroxide (k) was prepared by Lebedev K°3S\ / S03K N 1. 0 HN / X n ^ nh l 1 _ 2 ^ N 1-0 I 0 (1) (2) (3) (4)