How Does Energized NCCCCCN Lose Carbon in the Gas Phase? A Joint Experimental and Theoretical Study

Neutral NCCCCCN may be prepared in a collision cell of a VG ZAB 2HF mass spectrometer by charge stripping of (NCCCCCN)•−, formed in the ion source by the process NCCCCH(OEt)(CN) + HO− → H2O + NCCCC−(OEt)(CN) → (NCCCCCN)•− + EtO•. A comparison of the neutralization/reionization (−NR+) and charge reversal (−CR+) spectra of (NCCCCCN)•− indicate that some neutrals NCCCCCN are energized and rearrange to an isomer which decomposes by loss of carbon. An ab initio study at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G(3df) level of theory indicates that (i) triplet NCCCCCN is the ground state with a T/S energy gap of −14.9 kcal mol−1; (ii) the structures of triplet and singlet NCCCCCN need to be described by molecular obital theory, and a simple valence bond approach cannot be used for this system; and (iii) there are several possible routes by which an energized neutral may lose carbon, but the major route involves the triplet nitrile to isonitrile rearrangement NCCCCCN → CNCCCCN → NCCCCN + C