Ion-molecule reactions between ionized nitrile oxides and neutral nitrite

International audienceThe ion-molecule reactions of ionized nitrite oxide, R-C=N+-O-., with several neutral nitrites have been studied using both tandem mass spectrometric techniques and ab initio molecular orbital calculations. Ionized oxygen atom transfer as well as a formal substitution of nitric oxide by the neutral reagent in the radical cation were the main processes. Whereas the former reaction yields the corresponding ionized nitrite oxide, the second process gives an even electron species tentatively ascribed, following high-kinetic energy collisional activation experiments, to an aromatic azirinyl cation. All the experimental data point to a two-step reaction sequence where the primarily formed intermediate ions competitively dissociate by the loss of nitrite or of nitric oxide respectively giving nitrite oxide ions and azirinyl ions. From a theoretical point of view, the mechanism of the simplest reaction HCNO.+ + HCN --> cyclo-HCCHN+ + NO. has been explored at the MP2/6-31G(d) level of theory. The most favorable reaction profile involves the formation of a C-N bond between the positively charged carbon atom of HCNO.+ and the nitrogen atom of cyanhydric acid giving an HCNO.+/HCN intermediate which isomerizes into an ionized nitrosoazirine before losing NO.

Characterization of cyanogen N-oxide radical cation (NCCNO center dot+) in the gas phase by tandem mass spectrometry methodologies and ab initio calculations

On-line coupling of flash-vacuum pyrolysis and mass spectrometry has been applied to 3,4-dicyano-1,2,5-oxadiazole-2-oxide [1] (dicyanofuroxan). In agreement with previous work, it is found that 1 is almost quantitatively pyrolyzed in a 500-600 degrees C temperature range. Using collisional activation, the main pyrolysis products are identified as cyanogen N-oxide [2] and cyanogen (NC-CN). Dicyanoethyne (NCC=CCN) and carbon dioxide are also detected as minor products. The fragmentations observed in the CA spectrum of the [C2N2O](.+) ions (m/z 68) are in keeping with the proposed NCCNO connectivity and in good agreement with theoretical predictions. A peak of low intensity at m/z 40 (loss of CO) however suggests a partial contribution of isomeric cyano isocyanate ions, 3(.+). It is found that an homogeneous beam of cyanogen N-oxide ions is only obtained by dissociative ionization of 3,4-dicyano-1,2,5-oxadiazole [4] which loses intensively NCCN after ionization. Neutralization-reionization experiments confirm the stability of neutral cyanogen N-oxide in the gas phase. Calculated stability of the NCCNO neutral and the fragmentation energies of the NCCNO.+ radical cations (at the G2(MP2,SVP) level) are in good accord with the CA/NR experiments. Contrasting with the analogous cyanogen N-sulfide and N-selenide ions, cyanogen N-oxide ions do not exhibit significant ion-molecule reactions with various neutral targets (nitric oxide and pyridine). This unusual chemical behaviour is attributed to the stronger NO bond (higher double-bond character of the NO linkage) and the energetics (thermodynamics) of the oxygen transfer reactions

Synthesis of heptahelicene (1) benzo [c] phenanthro [4, 3-g ]phenanthrene.

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A new example of internal oxidation of remote groups in organic nitroaromatic ions

Intramolecular redox reactions occurring in ionized benzotriazoles and triazolopyridines bearing o-nitroaryl substituents on nitrogen produce ionized fulven-6-one and azafulven-6-ones

1-Synthesis of Octa- and Nonahelicenes. 2-New Synthesis of Hexa- and Hepta-helicenes. 3-Optical Rotation and O.R.D. of Heptahelicene

info:eu-repo/semantics/publishe

1-Synthesis of octa- and nonahelicenes. 2-New syntheses of hexa- and heptahelicenes. 3-Optical rotation and O.R.D. of heptahelicene.

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Formation and characterization of methoxy isothiocyanate (CH3ON=C=S) and methyl cyanate N-sulfide (CH3OC=N+-S-) as radical cations and neutrals in the gas phase

Dissociative ionization of heterocyclic precursors has provided a convenient source of isomeric [CH3O,C,N,S](.+) radical cations. Metastable ion (MI), collisional activation (CA), neutralization-reionization (NR) spectra, and ion-molecule reactions, performed in a hybrid tandem mass spectrometer of sectors-quadrupole-sectors configuration, have demonstrated the isothiocyanate, CH3ON=C=S.+ a, and the nitrile N-sulfide, CH3OC=N-S.+ b, connectivities. For the sake of comparison, a potential precursor of the isocyanate, CH3SN=C=O.+ c, was also investigated. The gas phase stability of the corresponding neutral molecules is indicated by the NR and NR/CA spectra. In addition, consecutive collisional activation processes (MS/MS/MS spectra) were used to characterize the structures of metastable ions which, in several cases, were found to be different from the corresponding ions generated in the ion source. Calculated ionization energies and enthalpies of reaction with NO. (at the G2(MP2,SVP) level) support the experimental characterization of ions a and b