Gas‐Phase ring‐chain tautomerism in 1,3‐oxazines. Does it exist?

Gas‐phase ring‐chain tautomeric equilibria with eight 2‐phenyl‐substituted perhydro‐1,3‐oxazines and six 2‐aryl‐substituted l,2‐dihydro‐4H‐3,1‐benzoxazines were studied by recording their mass spectra Finder different conditions. Their fragmentation behaviour was also studied using metastable ion analysis and exact mass measurement. For the monocyclic compounds the existence of tautomerism was apparent and it resembled that found in non‐polar solvents. In contrast, benzoxazines gave little evidence for the presence of the open‐chain forms.