SEARCH Articles Figures Tables Asphaltenes heteroatom structures Heteroatom-substituted crystal structure Heteroatomic structures carbon-heteroatom double bonds Polymers with heteroatom chain structure Ring structure heteroatoms Ring-heteroatom backbone structure STRUCTURE OF THREE-MEMBERED RINGS WITH TWO HETEROATOMS Structure of Five-membered Rings with One Heteroatom Structure of Five-membered Rings with Two or More Heteroatoms