Electron Affinities and Ionization Potentials of Aromatic Hydrocarbons

6 ELECTRON AFFINITIES AND IONIZATION POTENTIALS OF AROMATIC HYDROCARBONS 

The electronegativity of hydrocarbons is half the sum of the ionization potential plus the electron affinity, the Mulliken definition of the electronegativity of atoms. In the simplest approximation the electronegativity is constant and equal to the work function of graphite. This gives the relationship  

If two of these quantities are measured, then the third can be obtained. 

As more experimental values of both electron affinities and ionization potentials were measured, this relationship was tested. For the alternate aromatic hydrocarbons the EN is approximately 4.02 eV, as opposed to the work function of graphite that is 4.39 eV. The EN for the smaller aromatic hydrocarbons is 4.1 eV. The EN for hydrocarbons with hve-membered rings, 4.4 eV, and C l0. 4.5 eV, is closer to the work function of graphite. Table 4.4 gives the Ea, IP, and EN values for several hydrocarbons. From a larger set of data the EN is not constant. If the values for styrene, fluoranthene, naphthalene, styrene, and azulene are not included, then EN = 4.02 0.02 eV can be used to calculate either the Ea or IP. The calculated Ea are compared to the ECD values in Table 4.4 [10]. 

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