Benzene negative ion

Assume that the benzene negative ion, CsHg, has its unpaired elecUon in a delocalized orbital with equal magnitude at each of the protons. Predict the ESR spectrum. 

Figure 24.2 Diagram to Find the Spiittings in the ESR Spectrum of the Benzene Negative ion, CeHg.The...

The radical cation of benzene has been produced by y irradiation of benzene adsorbed on silica gel (62, 63). The seven-line spectrum shown in Fig. 24 is expected for a molecule having six equivalent protons. An experimental coupling constant of 4.4 G, compared to a value of 3.75 G for the negative ion, gives strong support for attributing the spectrum to a positive ion. The g value is also consistent with this assignment. 

Dougherty, R.C. Weisenbeiger, C.R. Negative Ion Mass Spectra of Benzene, Naphthalene, and Anthracene. A New Technique for Obtaining Relatively Intense and Reproducible Negative Ion Mass Spectra. J. Am. Chem. Soc. 1968, 90, 6570-6571. 

Of the radical ions derived from aromatic hydrocarbons, we mention the ions of benzene and tetracene. For benzene, both the positive and negative ions have been characterized by ESR spectroscopy. The radical anion shows seven evenly spaced lines ( H = 0.341 mT), ° suggesting that the spin density is distributed evenly over the six carbons (or that there is a fast equilibrium between structures corresponding to the two degenerate antibonding SOMOs Fig. 6.7). Introducing a single D is sufficient to disturb the equilibrium ( h = 0.3983 mT, 4H ah = 0.3454 mT,... 

The large red shifts observed in dichloromethane and benzene could not be exclusively accounted for by TCA-induced changes in the polarizability of the medium. The authors explained the effect by suggesting that the Coulombic interaction with a negative ion close to the PRSB is associated with a red shift rather than with the previously proposed (123,128-132,146) blue shift. This argument is difficult to accept since it leaves unexplained the basic spectral difference between PRSB in vacuum (theoretical) and in a nonpolar solution. Moreover, it is based on the... 

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