| Abstract
| - Parent 1-silaadamant-1-yl (1+) and a series of mono-β-silyl-substituted- (2-Me+, 2-F+, 2-Cl+, 2-Br+),bis-β-silyl-substituted- (3-Me+), and tris-β-silyl-substituted (4-Me+)-1-silaadamant-1-yl cations werestudied by the DFT method at the B3LYP/6-31G(d,p) level and by GIAO NMR at the B3LYP/6-31G(d,p)//B3LYP/6-31G(d,p) level. The geometries, relative energies, NMR chemical shifts, andcharge distribution in the bridgehead silylium ions are discussed and compared. The magnitude ofthe β-silyl effect (the Si−C−Si+ hyperconjugation) is gauged as a function of structure. Relatedmodel studies on the silabicyclo[2.2.2]octyl (5+, 6+, 5a+, and 6a+), silanorbornyl (7+ and 8+), andsilacyclohexyl cations (9+ and 10+) were carried out in which the effect of β-silyl substitution ongeometry, stability, and NMR chemical shifts was probed. The acyclic model Me3Si−CH2−Si+(Me)2(11+) was used to gauge the influence of the twist angle between the p-orbital at Si+ and the C−Sibond on relative stability and on the changes in the 29Si NMR chemical shifts. Finally, interactionof 1+ with H2O and MeOH and 2-Me+ with H2O was also examined. The resulting optimizedstructures (12+, 13+, and 14+) and the computed NMR chemical shifts are most compatible withthe formation of silaoxonium ions.
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