Why is a molecule rejected?

Dragon can process most of the common organic and inorganic molecules. However, some molecules can be rejected and this may depend either on a formally incorrect structure definition in the input file or on some restrictions fixed in Dragon.

If a molecule is rejected, the possible cause may be one of the following:

The molecule is a disconnected structure, e.g. two or more ions.
The molecule includes hydrogens with more than one bond.
The molecule includes a cyclic structure with too many circuits (i.e., fullerene derivatives, number of independent cycles more than 35 or the total number of circuits more than 4095).
The molecule includes at least one atom with unusual valence due to missing hydrogens or erroneous bond type specification.
The molecule includes at least one atom for which the quantity (number of valence electrons – number of bonded hydrogens – formal charge) = 0.
If the molecule is entered as SMILES notation, unrecognized symbols have been used or some other SMILES rules have been followed.