6829 T and n us. a electron-donor ability. The latter becomes more predominant when strongly electronwithdrawing groups or steric crowding decrease the otherwise dominant r-aromatic donor ability and allow the a-donor single bonds to compete. Thus, protolytic cleavage of alkylbenzenes and substituted alkylbenzenes depends on the nature and availability of T - , u-, and n-donor sites and the acid system used. Acknowledgment. The support of our work by the National Science Foundation and the donors of the Petroleum Research Fund, administered by the American Chemical Society, is gratefully acknowledged. Professor E. M. Arnett is thanked for samples of hexaisopropylbenzene and Professor M. S. Newman for samples of dineopentyltetramethylbenzenes.
( 6 1 8 ~ ) Parameters of the 1,4-Bicycl0[2.2.2]0ctyl Dication and Model Ions"
Table I. Proton ( 6 ~ and ) Carbon-I3 Dication 3.45,
4.14, sa 7 . 3 8 (NH)
1,4-Bicyclo[2.2.2]octyl Dication, a Novel Pseudoaromatic System1
Sir : We have succeeded in preparing the 1,4-bicyclo[2.2.2]octyl dication 1 under stable ion conditions.
+
3 n o t observed
5
sc
2.72, sd
George A. Olah,* Y. K. Mo Department of Chemistry, Case Western Reserve University Cleveland, Ohio 44106 Received February 9, I973
1
6H
61aCb -114.1 (CL) +149.3 (Cz)
1-128.6 (CJd +154.2 (Cz)
+147.3 (Cz).
4 . 1 9 (H2)
- 106.0 (CI)' +128.0 (C,)
3.90 (H2)
-110.9 (CI)'
4 . 2 0 (H2)
-129.5 ( C I ) ~
5 . 0 4 (CHz) 4.24 (CHI)
-137.8 (C+) +140.6 (CHs) +146.2 (CHa)
3.50 (Hz)' 2 . 2 0 (Hs, Hd 7.73 (NH)
+144.2 ( C Z ) ~ +169.7 (C,) +173.4 (C,)
5.85, sa
+121.1"
6
2
8.40 (NH)
n o t observed
The close approach of charged atoms and of "vacant" orbitals makes this novel and unexpectedly stable dication an intriguing subject for study. The CI. * . C 4 nonbonced separation in bicyclo[2.2.2]octane (2) is only 2.6 A ; the C1+. . .C4+distance in dication 1 would be expected to be even shorter. Although a number of 1,4 dications are known,2 none have positive centers held this closely together. Furthermore, alkyl-substituted 1,3 dications, which would have C f . . .C+ separations comparable to 1, have resisted attempts at preparation both in cage3 (3) and in acyclic (4) systems. The 1,4-bicyclo[2.2.2]octyl dication 1 formed from 1,4-dichlorobicyclo[2.2.2]octane (5)4 in SbF5-S02CIF (SO,) at -78". Ion 1 was found to decompose gradually at temperatures above -60". The dicarbenium (1) (a) Stable Carbocations. CLXII. (b) Taken in part from the Ph.D. Thesis of G. Liang, Case Western Reserve University, Cleveland, Ohio, 1973. (2) J. M. Bollinger, C. A . Cupas, I
