Substitution électrophile armatique. VI. Détermination des constantes σ⁺ pour les groupes Si(CH₃)₃ et Sn(CH₃)₃

Abstract

Rates of reaction between iodine and p‐trimethylsilyl‐ and p‐trimethylstannyl‐phenyl‐trimethyltin in methanol have been determined. These rates show that for the (CH3)3Si‐ substituent, the donor inductive effect and the withdrawing mesomeric effect of the metal cancel each other; for the (CH3)3Sn substituent, the donor inductive effect is preponderant.

Nucleophilic Reactivities of Tributylstannyl-Substituted Furans and Thiophenes

“…With this hypothesis, we can derive that a tributylstannyl group in the 2-position increases the reactivity of the 5-position of furan and thiophene by roughly 1500 (“ para ”-effect), comparable to the effect of a methyl group (Scheme ). The magnitude of this effect is quite remarkable since Hammett parameters suggest CH 3 (σ p + = −0.31) to be a much stronger donor than SnBu 3 (σ p + = −0.12) . It shall be noted that the corresponding effect of SiMe 3 resembles that of H more closely than that of CH 3 …”