MESO-IONIC COMPOUNDS By WILSON BAKER &LA. D.Sc. X.R.S. and W. D. OLLIS PH.D. (DEPARTMENT OF ORGANIC C~MISTRY THE UNIVERSITY BRISTOL) IN 1949 the term meso-ionic was introduced to describe a class of novel heterocyclic compounds of which the sydnones are the most closely investi- gated members. Since the proposal w