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

Abstract

(Chemical Equation Presented) 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. © 2005 American Chemical Society.