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The energetics of electron transfer from an extensive series of alkyl-substituted benzenes are measured both in solution and in the gas phase. The standard oxidation potentials stem from the reversible cyclic voltammograms (CV) in trifluoroacetic acid using the recently developed microvoltammetric electrodes. These values show an excellent correlation with the vertical ionization potentials 7p of the same aromatic hydrocarbons in the gas phase. Thermochemical analysis indicates that the slope of less than unity for the correlation arises mainly from solvation differences, particularly in the highly substituted polyalkylbenzenes. The values of £Ar°a lso correlate extremely well with the anodic peak potentials £p of the irreversible cyclic voltammograms, which can be readily measured in acetonitrile at a standard sweep rate. A slope of unity for the linear correlation is discussed in terms of the maximum error in the CV peak shift (£_ -£°) resulting from the electrochemical kinetics of the EC mechanism for arene oxidation. The correlation of E^0 and £p affords a prediction of the standard oxidation potential of benzene, which otherwise could not be measured directly. The same series of alkylbenzenes form stable x-complexes with chromium tricarbonyl that show reversible electrochemical behavior. The standard oxidation potentials £ArCr°o f the complexes also correlate very well with E^f of the free arene. The diminished slope of the correlation arises from the nonbonding character of the HOMO.The predicted value of E^0 for benzene from this relationship is in reasonable agreement with that obtained from the irreversible peak potentials.

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