Entering a formula will return all species with the same empirical formula. The characters * and ? can be used to indicate (0 or more) or (1 or more). For example C2H*F? will return all species with two C, zero or more H and one or more F and no other elements. A list of species that match the formula criteria is returned and one or more may be selected.
Going to the group selection page allows the selection of molecules with certain chemical groups, such as C=O bonds or NH2 groups. A list of species that match the group criteria is returned and one or more may be selected.