A COMMUNICATION1 on the above topic has just come to our attention, in which the authors have reasoned from some frequency calculations to the conclusion that cyclo-octatetraene probably has the D4d structure, with the D4 structure a less likely possibility. It is the purpose of the present note to point out that the vibrational spectra2 of the deuterium derivative of cyclo-octatetraene, published some time ago, enable the method of reasoning as well as the D4d conclusion to be refuted.