The a.c. and d.c. polarography of various aromatic hydrocarbons in dimethylformamide has been investigated. The addition of the first electron to the hydrocarbon molecule proceeds reversibly and is diffusion-controlled. The rate constant of electron transfer at the standard potential is practically the same for all hydrocarbons considered and amounts to 0-1 cm sec-1. The addition of the second electron is only reversible in a few cases. The irreversibility of the second reduction step of some compounds is at least for a great part due to proton addition to the doubly charged negative ion, which in these cases proceeds faster than the diffusion of the ion into the bulk of the solution.* A similar result was obtained by Breyer et aZ. 5 but in their formula the rate constant
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