Molecular structure, which is connected to a band is saturated or not stable. There is a general chemical formula is: n 2 CnH-6 such as benzene (C6H6, Benzene).
molecular structure which is connected in a circle is not enough, or do not have a stable chemical formula is common CnH 2 N - 6 such as benzene (Benzene, C H 6 6 ).