Syntheses of NCN and NC₃N from ionic precursors in the gas phase and an unusual arrangement of neutral NC₃N: A joint experimental and theoretical study

Abstract

Neutral NCN is made in a mass spectrometer by charge stripping of NCN-•, while neutral dicyanocarbene NCCCN can be formed by neutralization of either the corresponding anionic and cationic species, NCCCN-• and NCCCN+•. Theoretical calculations at the RCCSD(T)/aug-cc-pVTZ//B3LYP/6-31+G(d) level of theory indicate that the 3Σg- state of NCCCN is 18 kcal mol-1 more stable than the 1A1 state. While the majority of neutrals formed from either NCCCN-• or NCCCN+• correspond to NCCCN, a proportion of the neutral NCCCN molecules have sufficient excess energy to effect rearrangement, as evidenced by a loss of atomic carbon in the neutralization reionization (NR) spectra of either NCCCN+• and NCCCN-•. 13C labeling studies indicate that loss of carbon occurs statistically following or accompanied by scrambling of all three carbon atoms. A theoretical study at the B3LYP/6-31+G(d)//B3LYP/6-31+G(d) level of theory indicates that C loss is a consequence of the rearrangement sequence NCCCN → CNCCN → CNCNC and that C scrambling occurs within singlet CNCCN via the intermediacy of a four-membered C2v-symmetrical transition structure.