Hyperconjugation in β, β'-silyl substituted Vinylcations - Indications from IR Spectroscopy

Thomas Mueller (1) , Andrea Klaer (1)

1 University of Oldenburg

Alkyl substituted vinyl cations 1a-c have been synthesized in the form of their [B(C6F5)4] salts and have been characterized by NMR and IR spectroscopy. The IR absorption bands detected for the νas(C=C+) vibrations in vinyl cations are of great diagnostic value, due to their high intensity and due their relative isolated position in the IR spectra (Δν =1930-2020 cm 1). DFT calculations of the harmonic force constants at the B3LYP/cc-pvtz level of theory allowed for an unequivocal assignment of the band after scaling of the theoretical values to account for the anharmonicity of the experimental vibrational potential. A study on the energy of the νas(C=C+) of alkyl (1) and aryl substituted vinyl cations, 2, revealed a systematic trend, which indicates a decreasing stabilization of the vinyl cations by β-SiC-hyperconjugation when the electron donating ability of the substituent R2 next to the positively charged carbon atom is increased.

Mots clés: Physical Sciences

Thomas Mueller, Andrea Klaer. Hyperconjugation in β, β'-silyl substituted Vinylcations - Indications from IR Spectroscopy. Journal of Physical Organic Chemistry, 2010, 23 (11), pp.1043. ⟨10.1002/poc.1755⟩. ⟨hal-00589439⟩