Isomerisation du Benzoxazole et de L'anthranile Sous L'impact Electronique

Abstract

Une isomérisation des ions moléculaires précéde la fragmentation du benzoxazole et de l'anthranile (2,1‐ benzisoxazole) sour l'impact électronique.

Gas phase ion chemistry of the heterocyclic isomers 3-methyl-1,2-benzisoxazole and 2-methyl-1,3-benzoxazole

“…This species can eliminate CO, thus producing [7] ϩ⅐ , [9] ϩ⅐ , and eventually [16] ϩ⅐ , the latter two in agreement with the distinctive loss of ⅐ CH 3 from the ions at m/z 105 observed for 1. In the case of 2, the loss of CO and successive ring closures should yield the species [14] ϩ⅐ and [15] ϩ⅐ that are the most stable ion structures proposed for 2, and in agreement with the experimental data.…”

“…With regard to the structures of ions [M Ϫ CO] ϩ⅐ possibly produced by 2, the radical cation [16] ϩ⅐ is analogous to [9] ϩ⅐ , but the different arrangement of the C, N atoms in the side chain lets the latter structure more stable than [16] ϩ⅐ (⌬E [9] [14] ϩ⅐ in which the nitrogen atom is involved in the fusion between the two rings and whose structure might explain the loss of HCN as experimentally observed. The species [14] ϩ⅐ and [15] ϩ⅐ (⌬E [14] ϩ⅐ - [15] ϩ⅐ ϭ 4.01 kcal mol Ϫ1 ) are distonic ions and in both of them the unpaired electron is localized mainly on the carbon of the four-membered ring that binds one hydrogen while the positive charge is on the carbon atom at the fusion between the two rings.…”

“…It has been reported that the molecular ion of 1,3-benzoxazole isomerizes to 2-cyanophenol [14]. If it were the case also for its 2-methyl derivative 2, the 2-methoxycyanobenzene 3 should be produced.…”

“…The species [14] ϩ⅐ and [15] ϩ⅐ (⌬E [14] ϩ⅐ - [15] ϩ⅐ ϭ 4.01 kcal mol Ϫ1 ) are distonic ions and in both of them the unpaired electron is localized mainly on the carbon of the four-membered ring that binds one hydrogen while the positive charge is on the carbon atom at the fusion between the two rings.…”

“…As an example, the molecular ion of 2,1-benzisoxazole undergoes an opening of the five-membered ring producing an ion having the same structure to that produced by rearrangements of isatin and anthranilic acid [14]. Similarly, the study of the ion kinetic energy spectra of analogous thia isomers, i.e., 1,2-benzisothiazole and 1,3-benzothiazole, has evidenced their isomerization to common structure(s) under electron ionization [15].…”