Ionization energies of homologous organic compounds and correlation with molecular size

The empirical relationship IE ∝︁ 1/n, between the ionization energy (IE) and molecular size (as represented by the number of atoms, n) in homologous series of organic compounds has been confirmed for n‐alkanes, alkyl halides, cyclic ethers and alkyl‐subsiituted cycloalkanes. For each series, the plot of IE vs. 1/n produces a line of characteristic slope. The only exception is the cycloalkanes themselves, whose IE values (from C₃ to C₈) are closely similar. The possible relationship between the IE, the polarizability of the molecules and the energy of the highest occupied molecular orbital is briefly discussed.