Rotation barriers in N-substituted 2,4,6-trimethylpyridinium cations

The α-methyl and β-protons in ¹H-NMR spectra, the α-methyl, α-ring, and β-ring carbons in ¹³C-NMR spectra of N-substituted 2,4,6-trimethylpyridinium salts III are anisochronous. Dynamic NMR spectroscopy affords appreciably higher activation enthalpies ΔG≠ for rotation around the N(sp²)C(sp³) bond than ΔG≠ for the analogously substituted mesityl derivatives, in agreement with the shorter $\text{N}\text{+}$C than the CC bond.