Mass spectra of 1,2,3-triazoles

Abstract

The mass spectra of substituted 1,2,3-triazoles [RTR′, (1)](R′= H, CO₂X, COR″, pyrazolyl, or isoxazolyl) are discussed. For a wide variety of structural types, P⁺ is always strong and [P+ 1]⁺ is often of significant intensity. Subsequent breakdown patterns are strongly dependent on the substituents R and R′. The base peak, for example, may be [R″CO]⁺=[R′]⁺ in some oxotriazoles or [XO]⁺ in some esters (R′= CO₂X). Cleavage of the triazole ring may begin with one or more accessible cyclic (1H, 2H, or 3H) or acyclic (α-diazo-β-imino) parent ions [(1) or (3)] and lead initially to [P– N₂]⁺, [P– HCN]⁺, [P– RCN]⁺, [P– RCN₂]⁺, [RCN]⁺, [RCN₂]⁺, [RC]⁺, and related ions (m/e± 1). These might be regarded as the ‘standard’ unperturbed possibilities for (1). Thus, examples of the most prominent ions produced by cleavage of the triazole ring (RTR′) are: [P– N₂]⁺(R =p-O₂NC₆H₄, R′= CO₂Et), [P– HCN]⁺(R = Ph, R′= H), [RCN₂]⁺(R =p-ClC₆H₄ or p-MeOC₆H₄, R′= CO₂Et), [RCNH]⁺R,R′= COTR), and [RC]⁺(R = Ph, R = CHO). The mutual effects of ring and substituent are particularly striking in ditriazolyl ketones and in triazolylpyrazoles (5), where skeletal rearrangements of both rings are timed so that the maximum possible number of N₂are eliminated.