each of the atoms in a molecule must be presented by atom symbol from the periodic table. Symbols of unspecified atom A, Q, *, or R group labels are not allowed;
each of the bonds in a molecule must be covalent bond presented by single, double or triple bond types only;
structure must include three or more carbon atoms;
structure must include only one component. Single atom parts like HCl, Cl-, OH-, Na+, etc., (hydrogen atoms do not take into account) are excluded from MNA descriptors generation;
structure (main part, see the previous sentence) must be uncharged;
the absolute molecular weight of a substance must be less than 1250.