~ ~~~~Solvolysis rates of several adamant-I-yl ( = tri~yclo[3.3.1.1~~~]dec-l-yl) p-toluenesulfonates and bromides 2 identically substituted at C(3) and C(5) (twin substitution) have been determined and compared with the rates of the corresponding 3-monosubstituted compounds 1. As expected, the rate factors for twin substitution are much larger, but less than the square of the rate factors for single substitution. Also the rate factors per substitutent in 2 are considerably smaller than those for one substituent in 1. This attenuation is attributed to electron repulsion which limits the convergence of electron density to the cationic center. On the other hand, the inductivity for twin substitution @I = -2.55) is ea. twice as high as for mono-substitution @I = -1.26).Four kinds of polar substituent effects are discernible in solvolysis reactions of 3-substituted adamant-1-yl ( = tricyclo[3.3.1.13~7]dec-l-yl) bromides and tosylates ( = ptoluenesuljonates) 1 (X = Br and OTs, resp.), namely inductive, hyperconjugative, frangomeric, and homohyperconjugative effects [ 1] [2]. This follows from the reaction products and from the relationship between the rate constants k (in 80% EtOH) and the inductive constants o; [3] of the substituents. Alkyl groups and common electron-attracting substituents like COOCH,, OAc, Br, CN, and NO, as well as H-C(3) control rates of forination of the adamant-1-yl cations 5 by their inductive ( I ) effects only, as shown by the linear correlation of log k with the corresponding 07 values '). The latter were derived from the pK, values of 4-substituted quinuclidinium perchlorates 4 [3] which are also controlled by 1 effects.On the other hand, rates were 3 to 44 times higher than calculated from the regression line for log k us. 07, when R was a + M substituent or n electron donor such as OH, OCH,, or SCH,. These exalted polar substituent effects were attributed to C,C hyperconjugative relay of positive charge from the cationic center C( 1) to the substituents in the incipient cations 6 (the dotted lines imply weak bonding interactions). However, if the + M effect of the substituents were stronger, as in 1 (R = NH,, 0-, or S-), C,C hyperconjugation merged with concerted fragmentation [4] and led to accelerated formation of the corresponding bicyclic compounds 8 (R = NH:, 0, or S, resp.). In these cases, formula 6 represents the transition state for fragmentation to 8.Finally, the rates of 3-substituted adamant-1-yl bromides and tosylates 1 were 4 to 26 times higher than predicted by their O: values for R = CH,OH, COOQ, or (CH,),Sn [ 1][2].') According to the equation log k = pl.rri' + log k,.
