The major decomposition pathway involved in the fragmentation of derivatives of the title ring systems was the loss of RCN from the five-membered ring, except when this ring had a 3-amino, 3-hydroxyl or 3-mercapto substituent. In these cases, the exocyclic substituent and at least one nitrogen atom from the five-membered ring were lost.
IN RECENT years several reports have appeared of the isomerization of various ringfused s-triazole derivatives, such as the rearrangement of s-triazolo [4,3-a]pyridine into s-triazolo [I ,5-a]~yridine,~ s-triazolo [4,3-c]pyrimidine into s-triazolo [I ,5-c]pyrimi-dine3 and s-triazolo[4,3-a]pyrimidine into s-triazolo[l,5-a]pyrimidine.4 Though ultraviolet absorption spectral data5 are of considerable help in making structural assignments in this area, it was of interest to evaluate mass spectral fragmentation data in this context. This communication is based on a study of more than fifty isomeric s-triazolo [4,3-a]pyridines and s-triazolo [ 1 ,5-a]pyridines. Representative examples only are described here, either in the Figures or in Table 1. Metastable transitions associated with the observed transformations are listed in Tables 2 and3.
The members of this system studied gave a strong molecular ion which in many instances was the most abundant ion. The parent compound itself (1 ; R = R1 == H) (Fig. 1) showed only two fragmentation pathways (Scheme I). The molecular ion a lost HCN6 to give ion b (R1 = H), m/e 92 which, in turn, lost HCN to form the ion c, m/e 65. The other pathway involved elimination of nitrogen' from the molecular ion yielding the ion d, nz/e 91 which then lost HCN to give the ion [C,H,]+..