COMMUNICATIONS TO THE EDITUR
April 5, 1962
Further evidence for the concerted elimination may be derived from the p of the reaction, a low value (< 4) being associated with a more concerted elimination. As a corollary to this, one might predict that as the dihedral angle approached 90' from either 0 or B O ' , the elimination would approach ElCB and that p for the reaction would increase. These predictions are currently being tested. Using the above predictions, certain results reported in the literature become more meaningful. Cristol and Hoegger7 have reported that cis is faster than trans elimination in the bicycloheptyl system.
1313
known to be thermo~hromic,~ the exact nature of this phenomenon has not been investigated. In agreement with the earlier observations, solutions of I were found to become red on heating to 80looo, and to fade on standing a t room temperature. In addition, i t was found that the disappearance of the red color (Ama, 538 mp in CH3CN) was greatly accelerated by the addition of a variety of reagents including mineral acids, alkalies, bromine or oxygen. Significantly, the red color was destroyed instantaneously with bicyclo [2.2.1]heptadiene or dimethyl acetylenedicarboxylate, reagents known to be highly reactive toward dipolar ions4 Indeed, after heating a t 135-145" for four hours, solutions of I in these reagents were converted in good yields to the 1: 1-adducts, 111, m.p. 214-215", and IV, m.p. 170-171", respectively.s COOCH3 COOCHa
0 Ph
Obviously, a coplanar transition state is readilyavailable for cis elimination but very difficult for trans elimination. Further evidence in support of these predictions is derived from the study of 11,12-dichloro - 9,lO - ethanoanthracene by Cristol and Hause.* I n this system k-cislk-frans is about 8 and again it can be seen that for cis elimination a coplanar transition state can occur, whereas such a state is impossible (or nearly soj for trans elimination. (7) S. J. Cristol atid IC. 1:. IIoegger, J . (1!).57). ( 8 ) S. J. Cristol aiid N . I,. Haiisc, J . (1932). (9) Alfred P. Sloan Fellow.
(10) Shell Oil Fellow, 1961-196'2
111
0 Ph IV
The structures of these coinpounds were supported both by the shifts of the infrared carbonyl peaks (Nujol mulls) of I11 (5.89 p ) and dihydroIV (5.87 p ) from that of I (5.78 p ) , and by the close similarity of the ultraviolet spectra of I11 and dihydro-IV to that of tetralone. Compelling evidence for structure IV ultimately was obtained by treatment of IV with hot alcoholic alkali which led to the isolation of a CI8H1406 tricarboxylic acid and benzoic acid. The new compound had A m . Ciiem. S O L . 79, , 31:B a n m x . spectrum which showed a 0 : 2 ratio of
