Substituent effects of mono-, bis-, and tris(trimethylsilyl)methyl groups; determination of σ- and σ+-constants

Article abstract of DOI:10.1016/S0022-328X(00)80267-3

The apparent dissociation constants of the acids p-[(Me₃Si)_xCH_(3-x)]C₆H₄CO₂H in 50% aqueous ethanol at 25° have been measured and used to give the following σ-constants for the p-[(Me₃Si)_xCH_(3-x)] groups: x = 1, -0.29; x = 2, -0.33; x = 3, -0.27. The rates of solvolysis of the tertiary chlorides p-[(Me₃Si)_xCH_(3-x)]C₆H₄CMe₂Cl in aqueous acetone have also been measured and used to give the following σ⁺-constants: x = 1, -0.54; x = 2, -0.62; x = 3, -0.52. The results are consistent with the existence of substantial hyperconjugative electron release from the Me₃SiC bonds.