Gas‐phase conversion of tetrazoles to oxadiazoles: isolation and characterization of the N‐acylated intermediate

Abstract

The 5-substituted tetrazole ring was reacted in the gas phase with an acyl ion generated as the secondary reactive chemical ionization plasma in the mass spectrometer. The product ions obtained, among others, were proposed as the rearranged 2,5-disubstituted-1,3,4-oxadiazole nucleus. Its structure was demonstrated by comparison of the product ion spectrum of the 2,5-disubstituted-1,3,4-oxadiazole derivative obtained by condensed-phase reaction and the product ion spectrum of the oxadiazole derivative generated in situ by reaction of the 5-substituted tetrazole derivative with the acyl plasma. It was proposed that the mechanism of this transformation involved the presence of an acylated tetrazole intermediary, which could not be isolated in the condensed phase, followed by the rearrangement, with nitrogen loss, to afford the oxadiazole derivative. Under our conditions we were able to isolate the intermediate ion in the first field free region and demonstrate its structure by collision induced dissociation-tandem mass spectrometry.

Mass spectrometric fragmentation pathways of isotope labeled 2,5-disubstituted-1,3,4-oxadiazoles and thiadiazoles

“…The mass spectrometric fragmentation pathways of 1,3,4-oxadiazoles were studied by electron ionization (EI) [1][2][3], chemical ionization (CI) [4], electrospray ionization (ESI) [5] and liquid secondary ion mass spectrometry (LSIMS) [5,6].…”

The Abundances of Fragment Ions Formed via Skeletal Rearrangements from 2,5-Disubstituted-1,3,4-Oxadiazoles and Their Theoretical Calculated Stabilities

“…The EI-induced decomposition of 1,3,4-oxadiazoles was also studied [9][10][11] and complex skeletal rearrangement, consisting of the elimination of N 2 and CO molecules proceeded, leading to the formation of fluorene-type ions ([M -CO -N 2 ] +• ions). 10,11 Mass spectrometric fragmentation pathways of 1,3,4-oxadiazoles were also investigated by using so-called soft ionisation techniques such as chemical ionisation (CI), 12 electrospray ionisation (ESI) and liquid secondary ion mass spectrometry (LSIMS). 13,14 It was shown that protonated molecules of 2,5-diaryl-1,3,4-oxadiazoles lose isocyanic acid (HNCO) through complex skeletal rearrangement ([R -CN -R] + ions).…”

Differentiation of isomeric para‐ and meta‐substituted 2,5‐diphenyl‐1,3,4‐oxadiazole derivatives of anthracene by electrospray ionization tandem mass spectrometry

“…[11] A literature survey showed that few reports are available on mass spectral fragmentation of oxadiazole derivatives. [12][13][14][15][16][17][18][19] As these compounds belong to the category of organic light-emitting diodes (OLEDs) containing an oxadiazole group, the fragmentation behavior of these compounds under mass spectrometric conditions assumes importance and is desirable. These mass spectral studies may help in understanding the degradation process of these materials and in turn their stability and life.…”