The structure and rotational barrier for the mesityl‐silicon bond of 2,2‐dimesityl‐1,1,1,3,3,3‐hexamethyltrisilane have been investigated by 1H‐ and 13C‐variable temperature nuclear magnetic resonance (NMR) as well as by density functional theory structural calculations. The calculations show that the lowest energy structure has C2 symmetry with nonequivalent ortho methyl groups, consistent with the crystal structure and solution NMR. The nonequivalent ortho methyl groups exchange through a Cs transition state with a calculated relative free energy of 11.0 kcal mol−1. The barrier for this rotation found by dynamic NMR is 13.4 ± 0.2 kcal mol−1 at 298 K.

中文翻译：

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2,2-dimesityl-1,1,1,3,3,3-六甲基丙硅烷的计算和动态核磁共振研究

2,2-dimesityl-1,1,1,3,3,3-六甲基丙硅烷的 mesityl-silicon 键的结构和旋转势垒也已通过 1H 和 13C 变温核磁共振 (NMR) 进行了研究如通过密度泛函理论结构计算。计算表明，最低能量结构具有 C2 对称性，具有非等价的邻甲基，与晶体结构和溶液 NMR 一致。非等价的邻甲基通过 Cs 过渡态进行交换，计算出的相对自由能为 11.0 kcal mol-1。动态 NMR 发现这种旋转的障碍是 13.4 ± 0.2 kcal mol-1 在 298 K。