Carbon Participation in the Solvolysis of 6‐ and 7‐Substituted 2‐Norbornyl p‐Toluenesulfonates. Norbornanes, Part 11

Abstract

SummaryThe solvolysis rates and products of several 7-anti-substituted 2-endo-norbornyl p-toluenesulfonates 11 have been determined and compared with those of the previously reported 6-exo-substituted 2-exo-norbornyl p-toluenesulfonates 1. Although the number of bonds between the substituent and the reaction site is the same in the two series, the inductive effect of the substituents is transmitted far more strongly in the 6-exo-2-exo-series 1 than in the 7-anti-2-endo-series 11; i.e. their inductivities differ widely. It is concluded that through space induction involves graded bridging of the substituent-bearing C-atom to the incipient cationic center at C (2) and that this involves differential bridging strain. The different reactivities of unsubstituted 2-exo-and 2-endo-norbornyl derivatives can then be ascribed to a stereoelectronic effect.

ChemInform Abstract: NORBORNANES, PART 14. SOLVENT DEPENDENCE OF INDUCTIVITY IN THE SOLVOLYSES OF SUBSTITUTED NORBORNYL P‐TOLUENESULFONATES

“…2 ) . This finding confirms that bridging of C (6) or C (7) is insignificant in the transition state for the 2-endo-series 2 [l] [3], so that the more localized charge at C(2) tends to increase the importance of solvent ionizing power. Apparently, solvent nucleophility does not play an appreciable role.…”

“…These results confirm that, due to differential bridging strain, 2-norbornyl cations are anisotropic to polar effects.Introduction. -Recent studies [l] [2] [3] have shown that the solvolysis rates of the 6and 7-substituted 2-exo-and 2-endo-norbornyl p-toluenesulfonates (tosylates) 1, 2, 3 and 4 in 80% EtOH are strongly dependent on the position and orientation of the substituents relative to the nucleofugal tosyloxy group. In fact, the response of rates to the I-effect of the substituents, the so-called inductivity of the system'), varied from -2.0 for the series 1 to -0.72 for the series 4, although the number of bonds between the substituent and the reaction site is the same in all cases.…”

“…This would account for the lower inductivity of 2, namely -0.86, as compared to 1 (-2.0) [l]. The inductivity of 3, namely -0.97, is again somewhat increased due to the charge dispersal which accompanies the bridging of C (2) by the dorsal C (6) in the ionization to 8 [3].…”

Carbon Participation in the Solvolysis of Tertiary Norbornyl Derivatives Norbornanes. Part 15. 6‐substituted 2‐methylnorbornyl 2‐exo‐ and 2‐endo‐2,4‐dinitrophenyl ethers

“…Since bridging of C(2) by C (7) is at a minimum in the latter series [3] it should be negligible in the case of the series 2.…”

“…Meanwhile, it has been shown that the rates of the secondary 6-substituted 2-exo-norbornylp-toluenesulfonates (tosylates) 3 (X = OTsj are far more sensitive to the inductive ( I ) effect of the substituents than the rates of the 2-endo-epimers 4 [2] and of the 7-anti-substituted 2-endo-tosylates 5 [3]. This finding implied that inductivity [4] is especially high in the secondary 2-exo-6-exo-series 3 and led to the conclusion that through-space induction involves graded participation, or bridging, of C (6) in the ionization step.…”