Why are trimethylsilyl groups asymmetrically coordinated? Gas-phase molecular structures of 1-trimethylsilyl-1,2,3-benzotriazole and 2-trimethylsilyl-1,3-thiazole

The structures of 1-trimethylsilyl-1,2,3-benzotriazole and 2-trimethylsilyl-1,3-thiazole have been determined by gas electron diffraction and computational methods. While 1-trimethylsilyl-1,2,3-benzotriazole shows a significant asymmetry in the way the SiMe₃ groups bonds to the ring system, the same is not true for 2-trimethylsilyl-1,3-thiazole. However, it has been shown that when the positions of formal single and double bonds in the rings systems are considered, the silyl groups in both compounds are displaced towards the neighbouring ring nitrogen atom. Calculated structures of a series of analogous compounds with different substituents on silicon show only minor variations in the extent of the distortion, although with hydrogen instead of a silyl group the displacement is significantly smaller.