Hydrogen exchange at ring carbon in azolium ions and dimerization

3 Hydrogen exchange at ring carbon in azolium ions and dimerization 

Hydrogen atoms in azolium ions can be removed easily as protons (e.g. 300— 302) exchange with deuterium occurs in heavy water. The intermediate zwitterion (e.g. 301) can also be written as a carbene. The pKa values of thiazolium ions range from 16 to 20 (87CRV863, 88B5044). 

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