Restricted Rotation Involving the Tetrahedral Carbon. VII. Rotation About the Carbon-Group IV Single Bond

Abstract

Abstract 9-t-Butyl-, 9-trimethylsilyl-, 9-trimethylgermyl- and 9-trimethylstannyl-1,2,3,4-tetrachloro-9,10-dihydro-9,10-ethenoanthracenes were prepared by the addition of tetrachlorobenzyne to 1-(CH3)3M-substituted naphthalene. The carbon compound showed very high barrier to rotation, whereas the coalescence phenomenon of three methyl signals was observed for silicon, germanium, and tin compounds. The barrier (ΔG\eweq) to rotation at 298 K was obtained as 19.1±0.5, 17.2±1.2, and 11.7±0.4 kcal/mol for Si, Ge, and Sn compounds, respectively. The decrease in the barrier on increasing the atomic size was attributed to the release of repulsive interaction to a greater extent, since the longer bond length should result in the larger displacement of the methyl group even though the bond angle deformation is the same.