The neutral radical N¹³CCCO has been made by charge stripping of anion [N¹³CCCO]⁻ in a collision cell of a ZAB 2HF mass spectrometer. The precursor anion is formed in the ion source of the mass spectrometer by the loss of the elements of MeOH from the anion N¹³C–⁻CHCO₂Me. Neutral N¹³CCCO can, in turn, be charge stripped to the corresponding cation [N¹³CCCO]⁺ which then decomposes by competitive losses of CO and N¹³C˙. No losses of ¹³CO or NC˙ are observed in this spectrum: thus, the neutral N¹³CCCO does not scramble the carbons in the carbon chain during the lifetime (ca. 10⁻⁶ s) of the neutral. An attempt to form the neutral radical CC(O)(CN) (which is isomeric with NCCCO) from the precursor anion [CC(O)(CN)]⁻ was unsuccessful, since on formation, [CC(O)(CN)]⁻ undergoes facile rearrangement to the more stable [NCCCO]⁻. A theoretical investigation at the B3LYP/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory indicates that (i) there are singlet and triplet forms of [CC(O)CN]⁻ which are only 7 kJ mol⁻¹ different in energy, and (ii) both of these ions undergo facile rearrangement to form the respective singlet and triplet forms of [NCCCO]⁻ in strongly exothermic reactions.