Abstract
The structures of the molecules C(SiXMe2)4 (X=H, F, Cl, Br) have been determined by gas electron diffraction (GED). Ab initio calculations revealed nine potential minima for each species, with significant ranges of energies. For the H, F, Cl, and Br derivatives nine, seven, two, and two conformers were modelled, respectively, as they were quantum-chemically predicted to be present in measurable quantities. Variable-temperature 1H and 29Si solution-phase NMR studies and, where applicable, 13C NMR, 1H/29Si NMR shift-correlation, and 1H NMR saturation-transfer experiments are reported for C(SiXMe2)4 (X=H, Cl, Br, and also I). At low temperature in solution two conformers (one C1-symmetric and one C2-symmetric) are observed for each of C(SiXMe2)4 (X=Cl, Br, I), in agreement with the isolated molecule ab initio calculations carried out as part of this work for X=Cl, Br. C(SiHMe2)4 is present as a single C1-symmetric conformer in solution at the temperatures at which the NMR experiments were performed.
摘要
通过气体电子衍射(GED)确定了 C(SiXMe2)4(X=H、F、Cl、Br)分子的结构。Ab initio 计算揭示了每个物种的九个潜在最小值,其能量范围很大。对于 H、F、Cl 和 Br 衍
生物,分别模拟了九种、七种、两种和两种构象,因为根据量子
化学预测,这些构象的数量是可以测量的。报告了 C(SiXMe2)4(X=H、Cl、Br 和 I)的变温 1H 和 29Si 溶液相核磁共振研究,以及 13C 核磁共振、1H/29Si 核磁共振位移相关性和 1H 核磁共振饱和转移实验。在溶液中的低温条件下,C(SiXMe2)4(X=Cl、Br、I)各有两种构象(一种是 C1 对称构象,一种是 C2 对称构象),这与作为本研究的一部分对 X=Cl、Br 进行的孤立分子 ab initio 计算结果一致。