Reactivity of Cations versus Free Bases

Cations are much less reactive than the free bases, the reactivity difference being 107 4 between 1,3,5-trimethylpyrazolium ion and its free base, and 105 9 between 3,5-dimethylisothiazolium ion and 3,5-dimethylisothia- 

Logarithms or the Activating Effects of an Ortho-Methyl Substituent upon the Reactivit y of the 4-Position of Azoles  

Substituent l-Methyl- pyrazole 1-Melhyl- pyrazolium Isoxazole Isothiazole 1,2-Dimethyl- pyrazolium 

Logarithms of the Effects of Meta-Methyl Substituents in Azoles 

The relative positional deuteration rates have been determined for N-methylimidazolium ion in D2S04 at 163°C (positions in parentheses) as 1 (2), 73 (4), 120 (5) (74JOC2398), revised to 1 (2), 30 (5), 50 (4) (79JOC4240). This shows that the 4-position is the most reactive, whereas for the free base, the 5-position is predicted to be the most reactive. 

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