Secondary Deuterium Isotope Effects and Neighboring Group Participation Revisited

Studies on solvolytic reactions proceeding via neighboring group participation by means of secondary deuterium isotope effects are reviewed. The changes in magnitude of secondary KIEs are related to the degree of participation in the reaction transition state and these data are compared with other experimental evidence. Supporting information on the structure of carbocations is obtained by high level ab initio calculations. Isotope effect studies turned out to be among the most powerful tools available to chemists for elucidating the nature and structure of reaction transition states. »For progress there is no cure« J. von Neumann, 195

The Mechanism of Aromatization of 7-Norbornadiene Acetals. Evidence for Norcaradiene Formation

Dicarbomethoxy-tetraehloronorbornadienone aeetal le rearranges spontaneously to hemimelitate 3c while the corresponding anhydride 14 is stable up to 200oC. This result supports the hypothesis that the thermal rearrangement of substituted norbornadienes to aromatic products occurs by rate determining formation of norcaradiene intermediates

Allylic Cations in Solvolysis. A Case of Non-Participation

The rate constants and secondary deuterium Isotope ef\u27fects are measured in the solvo\u27lysis of various allyHc p-nitrobenzoates. The obtained results are explained by differences in inductive effects o>f vardous groups in the side-chain. These results are in keeping with the stepwise mechanism according to which neighboiring group n- and n-paxticiipation is not revealed in the studied solvCJ!lytic reactions

SECONDARY DEUTERIUM ISOTOPE EFFECTS IN SOLVOLYSES OF SMALL-RING COMPOUNDS

The importance of nonclassical ions as relatively stable intermediates in SN1- type reactions is a matter of considerable current controversy. A very important question in this controversy is the extent to which the observed rate accelerations are due to nonclassical electron delocalization in the transition states as compared to high initial state free energies because of steric strain

Solvolysis rate of 3-methyl-2- (3-pentynyl) · 2-cyclohexenyl p-nitrobenzoate. A model system for n-participation of the CC triple bond

The synthesis of 3-methyl-2-:(3-rpentynyl)-2-cycloheocenyl p-nitro1benzoa1te is desc["ibed. This ester so1lvolyzes in 97°/o CF3CH20H at 2'5 °C without n-participa:tion of the CC trLple bond, showing solvoiysis rate retardaition in comparison with the saturated anafog. This result is e~piained by electron-withdrawing inductiove e1ffect 01f 1the CC trirple bond. The lo.g k va~ues of alkanyl- (4), alikenyl- (5, 6), and alkyny:l-substitJu·ted (10) esters show good linear correia1tion With the pK. values of the cOirresrponding car:boxyJ'ic acids