Reactivities of Stable Rotamers. XVI. Tributylstannane Reduction and Electron-impact Mass Spectra of Rotamers of 1,2,3,4-Tetrachloro-9-(2-chloro-1,1-dimethylethyl)triptycene and 1,2,3,4-Tetrachloro-9-(2-chloro-1-chloro-methyl-1-methylethyl)triptycene