Comparison of Carbon−Silicon Hyperconjugation at the 2- and 4-Positions of the N-Methylpyridinium Cation

N-Methyl-2-trialkylsilylmethylpyridinium cations 6a−c and 4-trialkylsilylmethylpyridinium cations 5a−c were prepared and investigated using ²⁹Si and ¹³C NMR and single-crystal X-ray crystallography. Systematic differences in the ²⁹Si chemical shifts and ²⁹Si−¹³C one-bond coupling constants for these cations suggested that the Si−CH₂ bond interacts more strongly at the 2-position of the electron-deficient pyridinium ring than at the 4-position. This result is supported by the X-ray structures of the pyridinium cations 5b and 6b.