Formation and identification of ionized and neutral cumulenes, RNCCCNH, by tandem mass spectrometry

Abstract

Using a combination of mass spectrometric techniques, it is shown that 5-amino-4-cyanoisoxazole molecular ions (I+'), lose isocyanic acid HNC=O, not fulminic acid, HCGN + 0. Metastable ion fragmentations (unimolecular and collision induced) and deuterium-labelling experiments are in agreement with the formation of a cumulenic structure, HN=C=C=C=NH (3a"). The hitherto unreported molecules HNCCCNH are also shown to be stable when formed in the low-pressure gas phase of the mass spectrometer by using the technique of neutralization-reionization mass spectrometry. The arguments developed for the characterization of 3a +' have also been extended to the methylated and phenylated analogues 3b+' and 3c+' [ RN=C=C=C=NH+', R = Cfi, or C,H,I. On flash-vacuum pyrolysis at 7OO0C, 1 also loses HN=C=O producing the cumulene 3a, which is in turn readily tautomerized into malononitrile via wall collisions.

Carboxy(vinyl)ketene intermediates in the thermolysis of methylthio- and methoxy-substituted Meldrum’s acid derivatives

“…There are many examples of sensitive compounds (especially carrying O᎐H or N᎐H functions) isomerising extremely readily under FVT conditions to more stable tautomers in reactions formally involving 1,3-H shifts; in reality, these reactions are more likely bimolecular or wall-catalysed. 23 The observation that alkylthiomethyleneketenes such as 9 cyclise to thiophenones 11 (Scheme 3), whereas the oxy analogues 15 do not cyclise to furanones 17, is in good agreement with ab initio calculations of the activation barriers and energies of the zwitterionic intermediates (e.g.…”

Generation of New Nitrile N-Sulfides (NCCNS, R2NCNS, H3CSCNS, and ClCNS) as Ions and Neutrals in the Gas Phase: Tandem Mass Spectrometry, Flash Vacuum Pyrolysis, and ab Initio MO Study

“…Calculations (vide infra) have indeed indicated that a low-lying isomer HNCNSH •+ exists on the CH 2 N 2 S •+ potential energy surface and that rearrangement of NH 2 CNS •+ to HNCNSH •+ has a moderate energy barrier. The intensity of this peak is drastically decreased in the NR mass spectrum (Figure b) probably because of a higher energy deposition in the NR experiment . The very high intensity of the recovery signal at m / z 74 is again indicative of the stability of the neutral sulfide H 2 NC⋮N→S 7 in the gas phase.…”

Iminopropadienones, RN:C:C:C:O. Theory and experiment

“…2 We are currently extending this fruitful interplay between theory and experiment to the characterization of bisimines RN=C=C=C=NR'.3 Thecalculated CCC bending potential, however, is extremely flat.…”