Considering the π electrons in aromatic hydrocarbons as forming a two‐dimensional free‐electron gas, the Tomonaga method has been followed to determine the frequency of collective oscillations when an electron is excited in these systems. The calculated and experimental frequency have been found to be in excellent agreement, although the collective coordinate was not conjugate to the collective momentum in these systems containing only few free π electrons. Copyright © 1967 John Wiley & Sons, Inc.