7122 Table 11. Predicted Rate Constants for Reactive Bridgehead Systems Bingham force fielda AH(calcd),c k(calcd),d sec-l kcal/mol 70°, 80x EtOH
Compounds
l-Tricyclo[5.4.1.1~~9]tride~yl chloride (IV) 6-Tricyclo[4.4.1.l3~9]dodecylchloride (V)Q 3-Tricyclo[5.3.1.138s]dodecylchloride (VI)h l-Bicyclo[3.3.3]undecyl chloride (I, X = Cl) 3-Tricyclo[5.4.1.1~~~]tridecyl chloride (VII) l-Tricyclo[5.5.1.1~~~]tetradecyl chloride (VIII) 1-Tricyclo[5. 5.2.24 ’Oltetradecyl chloride (IX)i l-Bicyclo[4.4.4]tetradecylchloride (X)
-3.75 -3.87 -4.35 -6.77 -7.35 -8.05
2 . 6 x lo-’ 2 . 8 X 10-1 4 . 2 x 10-l 2.9 4.7 8.3
-14.94
2 . 0 x 103
9
Engler force fieldb AH(calcd),e k(calcd), sec-1 f kcal/mol 70”, 80% EtOH -3.64 -4.73 -6.13 -8.36 -8.32 -10.43 -17.38 -20.80
4.5 x 1.5 X 3.7 x 2.5 2.5 15. 5.4 x 1.2x
10-2 10-1 10-1
103 105
a See ref 3. * See ref 7. Difference of strain energy between carbenium ion and corresponding hydrocarbon. Calculated from eq 2. Difference of steric energy between carbenium ion and corresponding hydrocarbon. f Calculated from -log k(chlorides, 80% EtOH, 70”) = (0.37)AH 2.70, based on the treatment given in ref 6. 1,3-Bishomoadamant-6-yl chloride. l,l-Bishomoadamant-3-yl chloride. Hexahomoadamant-1-yl chloride.
e
+
N , X = C l , X’=H W, X = H, X’= C1
V
VI
Acknowledgments. We thank Dr. E. M. Engler for preliminary calculations. This work was supported at Princeton by grants from the National Science Foundation (GP-29078X), the National Institutes of Health (GM-19134), and Hoffmann-La Roche, Nutley, N. J., and at Stirling by Science Research Council (B/SR/ 52981). Computer time was supplied by Princeton University. Access to the Princeton Computer Graphics Laboratory, supported by the National Institutes of Health, and to computer programs written by Professor W. Todd Wipke facilitated this research. William Parker,* Roy L. Tranter, C. Ian F . Watt Chemistry Departmerit, Uniuersity of Stirling Stirling, Scotland
Laurence W. K. Chang, Paul v. R. Schleyer Department of Chemistry, Princetori Uriirersity
M
Princetori, New Jersey 08540 Receiaed April 27, 1974
X
hedral value1* and an sp2 hybridized carbon is more readily accommodated at the bridgehead. Flattening at the bridgehead also reduces the repulsive nonbonded interactions involving the C-3, C-7, and C-10 methylene groups. A similar, but smaller, solvolytic rate enhancement is exhibited by monocyclic cyclooctyl derivatives.I3 Since the three faces of I-C1 consist of chair-boat cyclooctane rings, the rate enhancement observed for I-C1 can be considered to be another manifestation of the “middle ring effect.”13 The success of our calculations in predicting bridgehead reactivities3s7 has led us to search for other reactive bridgehead systems by computation. All of the polycyclic systems listed in Table I1 are predicted by both force field treatments3” to be significantly more reactive than tert-butyl chloride. It has been observed recently14 that both 1,l-bishomoadamantane (VI-H) and 1,3-bishomoadamantane (V-H), like manxane (I-H), are not stable in air and form hydroperoxides. l-Chlorobicyclo[4.4.4]tetradecane(X), expected to be even more reactive than I-Cl, would appear to be an excellent objective for experimental investigation. (12) Engler’s force field6 gives the following bond angles for manxane: L C ~ C I C ~115.2”; , L C I C G , 118.8”; L C G C , , 118.2”. Similar values have been found experimentally for l - a z a m a n x a ~ i e . ~ ~ (13) See A. Streitwieser, Jr., “Solvolytic Displacement Reactions,” McGraw-Hill, New York, N. Y . , 1962, p 95; J. Sicher, Progr. Stereochem., 3, 202 (1962); H. C. Brown and I
