On the generation and identification of dimethoxycarbene and 2-oxazolidinylidene in the rarefied gas phase of the mass spectrometer

Abstract

Dimethoxycarbene radical cations, 1 + , are cleanly generated by the dissociative electron impact ionization of 2,2-dimethoxy-5,5-dimethyl-Δ 3-1,3,4-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 C 3H 6O 2 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 C 3H 5NO 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.