The e.s.r. spectrum of the 4.5-methylenephenanthrene dianion radical has been studied with particular interest in the variation of the alkali-metal splitting constant with the nature of the-solvent, the nature of the counterion, and temperature. The results may be interpreted in terms of interaction of the unpaired electron with one counterion only. The results also indicate that a variety of environments are possible for the counterion in the ' contact ' ion pair and that in particular cases an equilibrium is also present in which this counterion is in a ' solvent-separated ' environment. Interaction of the unpaired electron with the second counterion is not observed and is probably due to a solvent separated environment for this counterion.THE importance of ion pairing has been recognised for some time and the study of the nature and properties of ion pairs has recently received added impetus from e.s.r. ,ls2 conductance,3 and optical * measurements.In particular, a large number of e.s.r. investigations on the ion pairs formed between radical anions and alkali metal counterions have been made. These investigations have shown that the temperature-dependence of the alkali-metal hyperfine splitting for these ion pairs varies with the radical anion, the alkali-metal counter-
Minus Seventy ' thermostat bath was used for temperatures below $10" and a Tomnson and Mercer Bridge Controlled thermostat bath for temperatures above + 10".The temperature of the cell, measured by a copperconstantan thermocouple, remained constant to & 0.2' over the range of temperatures studied.Conductivity Measuremelzts.--X Wayne-Kerr universal bridge B221 was used for the conductivity measurements.
The reaction of fluorene with alkali metals a t -70" gives the fluorene radical anion. This decays at higher temperatures to the fluorenyl anion. The rate of the decay was found to be very sensitive to the nature of the counterion, i.e., AGI decreased markedly in the order Li+ > Na+ > K+ > Cs+. The decay can be of either the first or the second order, depending upon the nature of the counterion and of the solvent, and also on temperature. The e.s.r. spectrum of the radical anion has been studied and can be interpreted in terms of five sets of two equivalent protons.THE anion of fluorene has been studied in detail.1-3 It can be prepared at room temperature in a variety of solvents by bringing a solution of the hydrocarbon into contact with an alkali metal. The fluorenyl anion has created considerable interest owing to the sensitive nature of its absorption spectrum to the nature of the counterion, solvent, and temperature. The observed changes have been interpreted in terms of an equilibrium between contact and solvent-separated ion pairs, and also dissociated i0ns.l By analogy with the reaction of aromatic hydrocarbons such as naphthalene, biphenyl, and anthracene with alkali metals in ethereal solvents to form radical anions: it should also be possible, under suitable conditions, to form the radical anion of fluorene. Indeed, there is a report of this preparation in 1,2-dimethoxyethane at 88, 307, 318.
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