Reaction Sequences Involving the Mutual Interconversion of All 10 Tertiary Dimethyl-2-norbornyl Cations. A Comparison of Predicted Products and Rates with Experiment

Abstract

All 10 tertiary dimethyl-2-norbornyl cations have been prepared. There are sequences of individual steps which will in theory interconvert any given two of these cations, a total of 45 permutations. All of the possible sequences (within a defined limit on the allowable total number of steps) for performing these interconversions were determined using a digital computer. Each step used in the computer generated sequence had previously been assigned a trial activation free energy value and a comparison is made in this paper between the actual experimental rearrangement results (in terms of both the kinetics of disappearance for the cation and what product is in fact formed) and the predicted results.

A Kinetic and Thermodynamic Behavioral Comparison of Observable Secondary and Tertiary 2-Norbornyl Cations

“…2 or 3. That a C1 methyl probably does increase the stability of the secondary cation was alluded to previously (9) and can be demonstrated in several ways. The following arguments are illustrative rather than comprehensive: (a) The activation energy barrier separating the secondary and tertiary 'A second degenerate process can also be observed which interconverts the two methyl groups but there are at least three reasonable mechanisms for this.…”

“…The following arguments are illustrative rather than comprehensive: (a) The activation energy barrier separating the secondary and tertiary 'A second degenerate process can also be observed which interconverts the two methyl groups but there are at least three reasonable mechanisms for this. (9). This suggests either that the C1 methyl cation 8 starts off ca.…”

“…Degenerate Rearrangement in 1 2 Carbocation 12 has been reported (9). The kinetics of the degenerate endo-6,2-hydride shift can be best obtained using the two methyl groups.…”

“…Carbocation 4 has been reported (9). The kinetics of the degenerate Wagner-Meerwein shift -6,2-hydride shift -Wagner-Meerwein shift process (line broadening) were measured in exactly the same way as described for the 2-methyl cation 2 (8 Carbocation 3 was prepared from 3,3-dimethyl-2-exochloronorbornane (which rearranges via the 2,3-dimethyl isomer (15) eventually to 3) dissolved in a mixture of excess SbFS and S02ClF-S02F2.…”

Predicting the Most Favored Path and the Overall Rate of Multistep: 2-Norbornyl Cation Rearrangements. The Assignment of a Trial Activation Energy for Each Unique Step

“…One can then test the validity (predictive power) of these parameters on the rearrangement reactions involving the complete set of 10 tertiary dimethyl-2-norbornyl cations 1 (accompanying paper) (5). Six of these ions, and hence their rearrangement reactions, were completely unknown until after the formulation of the trial activation energy parameters and hence offered a genuine test of the validity of these.…”