497-28-9Relevant academic research and scientific papers
4. NORBORNANES. PART 19. THE INDUCTIVE MODEL FOR NORBORNYL CATION FORMATION
Altmann-Schaffner, Eva,Grob, Cyril A.
, p. 43 - 48 (2007/10/02)
Two CH3 groups at C(6) of 2-exo- (10a) and 2-endo-norbornyl p-toluenesulfonate 11a lower their solvolysis rates in 80 percent EtOH by factors of 28 and 16, respectively.A spirocyclopropyl group including C(6), as in 21a and 22a, reduces the rate of exo- and endo-ionization by factors of 250 and 8, respectively.The geminally dimethyl-substituted tosylates 10a and 11a yield the 2-exo-alcohol 10b, whereas the spirocycclopropyl-substituted tosylates 21a and 22a furnish rearranged 3-brendanol 23.These findings are readily rationalized by the inductive model, according to which norbornyl cation formation is controlled by the inductive effect of dorsal substituents.
Structural Effects in Solvolytic Reactions. 49. Steric Effects as a Major Factor in the Exo:Endo Rate Ratios for the Solvolysis of 2,7,7-Trimethyl- and 2,6,6-Trimethyl-2-norbornyl p-Nitrobenzoates
Brown, Herbert C.,Ikegami, Shiro,Jagt, Dawid L. Vander
, p. 1165 - 1171 (2007/10/02)
The exo:endo rate ratio for solvolysis, in 80percent aqueous acetone at 25 deg C, decreases from 885 for 2-methyl-2-norbornyl p-nitrobenzoate to 6.1 for 2,7,7-trimethyl-2-norbornyl p-nitrobenzoate.On the other hand, it increases remarkably to 3 630 000 in the case of 2,6,6-trimethyl-2-norbornyl p-nitrobenzoate.These changes are clearly attributable to steric effects caused by the syn methyl group at the 7- and 6-positions, respectively.In the 2,7,7-trimethyl-2-norbornyl system, the very low exo:endo rate ratio arises primarily from an increased rate of solvolysis of the endo isomer, attributed to relief in steric strain, involving the syn 7-methyl and exo 2-methyl groups, during ionization.The extremely large exo:endo rate ratio in the 2,6,6-trimethyl-2-norbornyl system is attributed to the high rate of solvolysis of the exo isomer, caused by the relief in steric strain involving the endo 2-methyl and endo 6-methyl groups, as well as an especially slow rate for the endo isomer, caused by enhanced steric retardation of ionization.Thus, these results show clearly that exo:endo rate ratios can be strongly affected by steric effects in the rigid norbornyl system.
Deamination Reactions, 40. Decomposition of 3,3-, 5,5-, and 7,7-Dimethyl-2-norbornanediazonium Ions
Kirmse, Wolfgang,Brandt, Sigrid
, p. 2510 - 2523 (2007/10/02)
gem.-Dimethylnorbornyl cations (3, 5) were generated by decomposition of optically active diazonium ion precursors. 6,1- and 6,2-H shifts were detected by structural isomerization and racemization, respectively.Product distributions and optical activities were profoundly affected by the polarity of the solvent.In weakly polar solvents, substitution reactions were associated with much less racemization than hydrogen shifts.Our observations are incompatible with equilibrating open ions but are reasonably explained in terms of unsymmetrical ion pairs.
