COMMUNICATIONS TO THE EDITOR
1178
CaHe
Reply to CcCommenton ‘Ionic Species Formed from Benzene during Radiolysis of Its Solutions in 3-Methylpentane at 77’K’
CeHa”
Publication costs assisted by A . Elcstrom
Sir: In reply to Brocklehurst’s comments we would like to draw attention to the following. 1. Brocklehurst suggests that the 320-nm band, which we attribute to the benzene monomer cation, may be due to the cyclohexadienyl radical. However, the spectrum of the cyclohexadienyl radical shows a very distinct fine structure‘ which is totally absent in the 320-nm band found in 3MP-CaH6-CC14 mixtures. 2. We observe that the yield of the species absorbing a t 320 nm is increased by the addition of CCL. This behavior is commonly accepted as evidence of a cationic speciesO2J If the 320-nm band were attributed to a cyclohexadienyl radical, it is difficult to arrive at a plausible mechanism for the enhancement of its yield in the presence of CCL. 3. As pointed out above, the cyclohexadienyl radical is readily observed in methanol solutions containing benzene which were irradiated at 77°K.’ It is believed to be formed by the reactions
The Journal of Phyekal Chem&Ty, Vol. 76, No. 8,1071
+ e- +CsHa-
(1)
+ ROH +CaH? + RO-
(2)
Thus in the alcohols the benzene anion and its dimer are not stable. However, in solvents which are not able to react with CaH6- by a reaction analogous to eq 2, the benzene anion and its dimer would be expected to be observed. It is therefore not possible to make general statements regarding the stability of the benzene anion and its dimer in a variety of solvents which have greatly different polarities. 4. Brocklehurst has not offered any explanation for the unusual concentration dependency of the 525-, 930-, 320-, and 1030-nm bands which we have observed. While it is quite possible that our assignments may be in error, the alternatives offered by Brocklehurst do not appear t o satisfy the observed results. (1) T. Shida and W. H. Hamill, J . Amer. Chem. Soc., 88,3689 (1966). (2) D.W.Skelly and W. H. Hamill, J . Phys. Chem., 70, 1630 (1966). (3) E.Wiseall and J. E. Willard, J . Chem. Phys., 46,4387(1967).
CHEMISTRY DIVISION AUSTRALIANATOMICENERGY COMMISSION AUSTRALIA LUCAS HEIGHTS,SYDNEY, RECEIVED NOVEMBER 5, 1970
A. EKBTROM
