Comparison of carbon-silicon hyperconjugation at the 2- and 4-positions of the N-methylpyridinium cation.

[structure: see text] N-Methyl-2-trialkylsilylmethylpyridinium cations 6a-c and 4-trialkylsilylmethylpyridinium cations 5a-c were prepared and investigated using (29)Si and (13)C NMR and single-crystal X-ray crystallography. Systematic differences in the (29)Si chemical shifts and (29)Si-(13)C one-bond coupling constants for these cations suggested that the Si-CH(2) 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.