ESCHERA Computer Program for the Determination of External Rotational Symmetry Numbers from Molecular Topology

An algorithm for determining the external rotational symmetry number of a molecule from a SMILES string has been developed. ESCHER operates by first locating the center or centers of graphical symmetry for the molecule and the equivalence classes of atoms connected to the center or centers. The center(s) of graphical symmetry is the atom(s) which is(are) most symmetrical with respect to the connections to other atoms. These are then used to calculate the symmetry number, σ.