Zwitterionic piroxicam in polar solution

The selective broadening of 13C NMR lines in solutions of piroxicam in polar solvents is related to the equilibrium with its zwitterion by reference to the CP/MAS spectra of the known crystalline solids. The amount of zwitterion in N,N-dimethylformamide solution at 205 K., in which the interconversion is slow enough to allow the separate spectra to be assigned, is 19%.