159s
R. A. SNEEN,R. W. [CONTRIBUTION FROM THE
JENKIXVS, JR., AND F.
DEPARTMENT OF
CHEMISTRY,
L.RIDDLE,JR.
1701. s4
PURDUE UNIVERSITY. LAFAYETTE, IND.]
On the Question of Anchimeric Assistance by Phenyl Participation. The ,&Isotope Effect on Acetolysis of 2,2-Dideuterio-5,5-diphenylcyclopentylp-Toluenesulfonate B Y RICHARD A. SNEEN, ROBERT w. JENKINS, J R . , ~ AND FLOYD L.RIDDLE,JR.' RECEIVED JULY 12, 1961 2,2-Dideuterio-5,5-diphenylcyclopentanoland 2,2-diphenylcyclopentanolhave been prepared and converted into their p-toluenesulfonate esters. The undeuterated ester underwent acetolysis at 50' with a rate constant of 6.54 f 0.17 X sec. -I, greater by a factor of 1.76 than that of cyclopentyl p-toluenesulfonate. Further the dideuterio-diphenyl ester reacted a t a rate 0.85 f: 0.04 times t h a t of its dihydro analog, corresponding t o a difference in free energies of activation of 54 f 16 cal./deuterium atom. This value is t o be compared with the corresponding values of 110-127 cal./deuterium atom reported by Streitwieser and co-workersz for cis- and trans-2-deuteriocyclopentylp-toluenesulfonate. It is argued t h a t the decreased sensitivity of reaction rate to &deuterium substitution observed with the diphenylcyclopentyl esters indicates considerable dispersal of positive charge in these transition states, perhaps most reasonably by a mechanism involving phenyl participation.
In numerous recent s t u d i e ~ ~ i t -has ~ been found The intermediate 5-cyano-2,2-diphenylcyclopentathat the effect of replacing &hydrogen by deuterium noneimine had been prepared by these authors by atoms has been to reduce substantially the rates of the sodium t-butoxide-catalyzed condensation of solvolysis of certain organic esters and halides. 2,2-diphenyladiponitriIe in solvent t-butyl alcohol ; Although the mechanism by which this effect oper- this compound, in turn, had been prepared by the ates has not been clearly defined, certain features sodium amide-catalyzed reaction between diphenylof the phenomenon have emerged and some gener- acetonitrile and ?-chlorobutyronitrile in benzene. alizations can be drawn. We have found that the cyclic imine can be more In the first place the effect appears to be cumula- conveniently prepared directly (70y0)from the tive; each successive replacement of a ,&hydrogen latter reactants when they are treated with 2 moles atom of a given degree by deuterium results in a of sodium amide in liquid ammonia. nearly constant raising of the free energy of activaUahH + CICH,CH,CHKN tion. Furthermore, the magnitude of the rate de- (c6ir5~2c~~cx celeration effected by &deuterium substitution (GjH5j2(,XN appears to be defined by rather narrow limits for a variety of compounds under various solvolytic conditions and appears to vary in an important liq SH H2c: H,C s way only with the degree of alkyl substitution a t >!
