The Behavior of Radical Anion of Acridine as Revealed from ESR Studies

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Abstract
Nature of acridine anions produced by the addition of alkali metals to the tetrahydrofuran solutions of acridine has been studied by means of ESR and VU spectra. In excess of acridine (A), a green species G is produced. This has been identified as A−Na+ (or A−K+ etc.). A−Na+ gives under suitable conditions, ESR spectra with hfs consisting more than fifty lines. This species reverts to acridine upon addition of a small quantity of water or ethanol. With the fall of temperature, the intensity of ESR spectra of G decreases remarkably and accompanied with it, UV spectra of G also decline with no change of the spectral shape, logIvs. 1/T plots where I is either the intensity of UV absorption or of the ESR signal are satisfactorily linear; this has been interpreted to be due to a large equilibrium constant of the process, 2A− Na+\ightleftarrows(Na+A−)2 in which (Na+A−)2 is a colorless diamagnetic substance. This interpretation has led to the value of enthalpy of dissociation of (Na+A−)2 as ca. 14 kcal. When sodium is in excess, a diamagnetic violet species is produced. This has been assigned as Na+A2−Na+. The chemical processes pertaining to A−Na+ and Na+A2−Na+ can be summarized as follows: (Remark: Graphics omitted.)