戊撐; 環戊烷
Pentamethylene \Pen`ta*meth"yl*ene\, n. [Penta- + methylene.] (Chem.) A hypothetical hydrocarbon, {C5H10}, metameric with the amylenes, and the nucleus of a large number of derivatives; -- so named because regarded as composed of five methylene residues. Cf. {Trimethylene}, and {Tetramethylene}.