2-Cyanocyclopentanone imine 2-Cyanocyclopentylidenimine 2-Iminocyclopentanecarbonitrile 2321-76-8 BRN 2689609 CYCLOPENTANECARBONITRILE, 2-IMINO- EINECS 219-033-9 NSC 141554 USAF A-1967