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

Abstract

Observable 2-norbornyl cations undergo at least five different rearrangement reactions, all of which are known from previous work on this system. In this paper, these rearrangement categories have been subdivided to reflect secondary-tertiary energy and rate differences and a trial set of activation free energies AG* is derived for each subdivided step. The most important of these parameters is the energy difference between secondary and tertiary (methyl) systems which was estimated as 5.5 kcal/mol. These parameters allow one, for the first time, to make a rational assessment of the overall reaction course of multistep rearrangement reactions in this system, for example, those observed in a number of bicyclo[2.2.1]heptyl(norbornyl) terpene systems.R. HASELTINE, E. HUANG, K. RANAGNAYAKULU, T. S. SORENSEN et N. WONG. Can. J. Chem. 53,1876Chem. 53, (1975

Structural effects in solvolytic reactions. 27. Solvolysis of the exo- and endo-1,2-diphenyl-2-norbornyl and -1,2-dimethyl-2-norbornyl p-nitrobenzoates and chlorides. Evidence for the classical nature of 1,2-disubstituted tertiary 2-norbonyl cations and structure of the parent 2-norbornyl cation

“…32 39 The formation of the second isomer can be followed by the appearance of two new methyl peaks in the NMR spectrum and by the formation of an isomer which undergoes solvolysis at a rate Vng that of the original chloride. Both isomeric chlorides, which were not separated, undergo hydrolysis to the same alcohol (33). At equilibrium the two chlorides are present in the ratio 70% 32/30% 39.…”

“…The endo alcohol (30) was converted into the exo chloride (32) by treatment with hydrogen chloride in an automatic hydrochlorinator. 22 The chloride was then hydrolyzed in buffered aqueous acetone to yield 1,2-dimethyl-exo-norbornanol (33), which was converted into the p-nitrobenzoate16 (34) (eq 15).…”

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

“…a CI Hydrogen Let us start by deriving an estimate of the energy difference between a 1,2-di H (secondary) and a 1,2-di CH, (tertiary) norbornyl cation. A value of 5.5 kcal/mol has been previously derived (8) for the secondary-tertiary (methyl) energy difference using the activation energy for a degenerate rearrangement occurring in 2. The 2,4-dimethyl-2-norbornyl cation 4, likewise undergoes this same degenerate rearrangement' (eq.…”

“…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. The concentration limit was about 1 0 z w/v in order that precipitation did not occur at the very low temperatures.…”

Energy separation between secondary and tertiary bicyclo[2.1.1]hexyl cations. Partial bridging in carbocation structures

“…1-Methyl-2-bicyclo[2.1.1]hexanone (4) was prepared from 2methyl-1,5-hexadien-3-ol (prepared via a Grignard reaction using the method of Dreyfuss29) by a procedure analogous to that given above:8 IR 1759 cm"1; NMR (CDCI3) 2.66(1 H, m), 2.14(2 H, m), 2.00…”