Abstract
1,4- and 1,5-disubstituted tetrazoles possess enriched structures and versatile chemistry, representing a challenge for chemists. In the present work, we unravel the fragmentation patterns of a chemically diverse range of 5-allyloxy-1-aryl-tetrazoles and 4-allyl-1-aryl-tetrazolole-5-ones when subjected to electron impact mass spectrometry (EI-MS) and investigate the correlation with the UV-induced fragmentation channels of the matrix-isolated tetrazole derivatives. Our results indicate that the fragmentation pathways of the selected tetrazoles in EI-MS are highly influenced by the electronic effects induced by substitution. Multiple pathways can be envisaged to explain the mechanisms of fragmentation, frequently awarding common final species, namely arylisocyanate, arylazide, arylnitrene, isocyanic acid and hydrogen azide radical cations, as well as allyl/aryl cations. The identified fragments are consistent with those found in previous investigations concerning the photochemical stability of the same class of molecules. This parallelism showcases a similarity in the behaviour of tetrazoles under EI-MS and UV-irradiation in the inert environment of cryogenic matrices of noble gases, providing efficient tools for reactivity predictions, whether for analytical ends or more in-depth studies. Theoretical calculations provide complementary information to articulate predictions of resulting products.
Highlights
Tetrazole [1] and derivatives have attracted perennial attention for several decades due to their structural features and unique reactivity traits, as well as relevant applications [2,3,4,5,6,7].Among the main features responsible for the wide array of applications of tetrazoles are the acid/base and electron-withdrawing properties of the heteroaromatic ring
A library of 5-allyloxy-1-aryl-tetrazoles 2a–h and 4-allyl-1-aryl-tetrazole-5-ones 3b-h was studied to elucidate the behaviour of the compounds when subjected to electronically induced fragmentation in electron impact mass spectrometry (EI-MS). 5-allyloxy-1-aryl-tetrazoles 2 were prepared from the reaction of 5-chloro-1-aryl-tetrazoles 1 with the respective allyl alcohol in an alkaline medium, as depicted in Scheme 1
Structures, molecular ions [M]+‧ and significant fragmentary ions registered in the electron ionization (EI)-MS spectra of the studied 5In continuation of the study, we evaluated the behaviour of the series composed of the allyloxy-1-aryl-tetrazoles, accompanied by the respective relative abundancies
Summary
Tetrazole [1] and derivatives have attracted perennial attention for several decades due to their structural features and unique reactivity traits, as well as relevant applications [2,3,4,5,6,7]. Studies on the photochemistry of some substituted tetrazoles have shown that the preferential structures formed from photocleavage are azides, aziridines and isocyanates, with the nature of the substituents attached to the tetrazole ring strongly influencing the fate of photoreactions, whether due to their chemical nature, the possibility of cross-reactions or conformational impairments [16,27,28,29]. The results gathered using the EI-MS technique are compared with those obtained from UV-induced photolysis of monomeric tetrazoles isolated in cryogenic matrices of noble gases [12,30] to further assess the degree of comparability between the fragmentation patterns obtained using the two forms of excitation, as this analysis can provide a useful complementary technique in reactivity studies of this class of molecules and possibly others
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