One of the present authors introduced a parameter, named 'azimuthal angle' phi, aimed at distinguishing between isomeric molecules, especially between isomers whose molecular graphs are isospectral. In a recent Letter [Chem. Phys. Lett. 364 (2002) 463] an upper bound for phi was established. Unfortunately, this upper bound is erroneous. We now show that, based on the considerations in the mentioned Letter, the azimuthal angle cannot be determined and it may assume any value between 0 and 2pi. (C) 2003 Elsevier B.V. All rights reserved.