J . A m . Chem. Soc. 1988,110, 4117-4120 cation shows that it is closest to that theoretically predicted for a partially methyl-bridged structure.
Acknowledgment. S.A.J. thanks Drs. Bill Brennan, Hugh Munro, and Dick Hutton for many stimulating discussions and the SERC for provision of a research studentship. We thank Rob Allaker for preparing the norbornyl chloride and Dr. Gerald
41 17
Brooke for providing the butene. Registry No. Antimony pentafluoride, 7783-70-2; terr-butyl chloride, 507-20-0; exo-2-norbornyl chloride, 765-91-3; 2-norbornene, 498-66-8; fluorosulfonicacid, 7789-21-1;cis-but-z-ene, 590-18-1; tert-butyl cation, 14804-25-2; 2-norbornyl cation, 2432 1-8 1 - 1 ; sec-butyl cation, 1654859-7
a / n Interactions in [ 2.2lParacyclophanes. PE Investigations
on Octamethyltetrasila[ 2.2lparacyclophane and Octamethyltetrasila[ 2.2]( 2,5)thiophenophane and -furanophane Rolf Gleiter,**+Wolfgang Schafer," Gerhard Krennrich,"and Hideki Sakurai*.l Contribution f r o m the Institut f u r Organische Chemie, Unicersitat Heidelberg, 0 - 6 9 0 0 Heidelberg, West Germany, and Department of Chemistry, Tohoku University, Sendai 980, Japan. Received November 13, 1987
Abstract: The photoelectron spectra of I , I ,2,2,9,9,10,10-octamethyl1,2,9,10-tetrasila[2.2]paracyclophane(6a) and the related octamethyltetrasila[2.2](2,5)thiophenophane (7a) and -furanophane (8a) have been recorded. The sequence of the first bands of these spectra is assigned by comparison of the ionization energies with calculated orbital energies. A comparison between the band sequence of 6a and that of [2.2]paracyclophane ( 1 ) shows a smaller through-space and a larger through-bond interaction for 6a. The through-bond interaction between the b3,(a) orbital and the corresponding T orbital yields a different orbital sequence in 6a as compared to 1. A similar strong through-bond interaction as in 6a has been encountered in 7a and 8a as shown by comparing the PE spectra of the latter compounds with [2.2](2,5)thiophenophane (10) and [2.2](2,5)furanophane (11).
The He 1 photoelectron (PE) spectrum of [2.2]paracyclophane (1) shows a broad first band between 8.0 and 8.4 eV, well separated from two smaller bands at 9.65 and 10.3 eV.' It is generally - Ir L
e
-,-r--
$ ;+(?+
