Dimethoxycarbene radical cations, 1+, are cleanly generated by the dissociative electron impact ionization of 2,2-dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline, I. Using the technique of neutralization—reionization (NR) mass spectrometry, it is shown that reduction of 1+ yields the neutral carbene 1 as a stable species in the rarefied gas phase. The collisional activation mass spectra of the m/z 74 C3H6O2 ions generated by very low vapour pressure pyrolysis—mass spectrometry of I show that the carbene 1 can also be generated by pyrolysis but only in admixture with its isomer methyl acetate. The above techniques were also employed to study the m/z 71 C3H5NO ion generated from 3,4,9-triaza-2,2,-dimethyl-1,6-dioxaspiro-[4,4]non-3-ene, II. NR experiments on this ion show that the cyclic carbene 2-oxazolidinylidene, 2, is a viable species in the gas phase. The pyrolysis experiments indicate that it rapidly isomerizes to 2-oxazoline, 2a.