 Molecular graphs can distinguish between structural isomers, compounds which have the same molecular formula but non-isomorphic graphs - such as isopentane and neopentane.On the other hand, the molecular graph normally does not contain any information about the three-dimensional arrangement of the bonds, and therefore cannot distinguish between geometric isomers (such as "cis" and "trans" 2-butene) or other stereoisomers (such as D- and L-glyceraldehyde).In some important cases (topological index calculation etc.)