Phenoxyl radicals and their derivatives have been prepared by flash photolysis in gaseous and liquid systems, by chemical oxidation and by photolysis of rigid solutions. Their spectra have been recorded and the longer wavelength system, expected on theoretical grounds, has been observed. Investigations of the spectrum as a function of pH show that these radicals are very weak bases and that, contrary to the interpretations of some other workers, the spectra observed under all conditions except those of very high acidity are to be attributed to neutral unprotonated radicals.

Two processes of side-chain fission have been identified in the photolysis of substituted aromatic molecules in rigid solvents at low temperatures. One involves fission of a fi bond to yield two radicals and the other results directly in the formation of two molecules, one of which is styrene. Quantum yields at 2537A in one example of each process, were 1.1 x 10-2 and 3.6 x 10-2 respectively. The radical products have been identified spectroscopically and conditions necessary for their stabilization have been investigated. Generalizations concerning the relative probability of dissociation of different bonds in equivalent positions are applicable to the forty molecules which have been studied.The primary photolytic bond dissociation processes in aromatic compounds have received relatively little attention owing to the low quantum yields of dissociation and the difficulties of analysis of the complex products which are often formed. Previous studies have been based mainly on analysis of the gaseous products of reaction and the work most relevant to the present discussion is that of Hentz, Sworski and Burton 1s 2 who found evidence for fission in the side chain of toluene with a quantum yield of gaseous products of about 1 %.The method which we have used here is one which eliminates the complexities of secondary reactions. It is based on the observations of Norman and Porter 3 who found that toluene and related molecules dissociate photochemically in rigid media and that aromatic free radicals remain trapped in the matrix at low temperatures, and can be observed spectroscopically. The spectra were first observed following flash photolysis of aromatic vapours by Porter and Wright (part 3) 4 and were attributed to benzyl and its derivatives. It has recently been shown that they are also formed during photolysis of ordinary solutions at normal temperatures.5 Whilst further studies in gases and liquids will be necessary for the interpretation of the kinetics of the radical reactions, the matrix isolation technique is in many ways more suitable for the identification of the radical spectra and of primary photochemical processes owing to the elimination of most secondary reactions. EXPERIMENTALThe apparatus and procedure used in the main part of this investigation were identical with those described by Norman and Porter,3 the cell length being 1.5 cm. In later experiments a different arrangement incorporating a cell 20 cm in length was used to detect weaker transitions.6 Spectra were recorded by means of the Hilger medium and small quartz instruments and scanned by microdensitometer. All solvents were spectroscopically pure and were carefully dried in order to prevent crystallization of the glass. The aromatic compounds available as commercial products were purified by fractional distillation, recrystallization or vacuum sublimation and boiling points or melting points in every case were within one degree of those reported in the literature. Some of the particular methods used were : toluene, ethyl benzene, isopropyl ben...

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