New 1H and 13C NMR 400 MHZ spectra of the 2-Nb cation under stable ion conditions, e.g., in SbF5 / SO2F2 / SO2ClF, – 80 o C, show besides the usual 1H NMR resonances at δ4.93 (4H), 2.82 (1H), 1.85 (6), the never before seen singlet, δ 9.63, and doublet, δ 2.97 (J2,6 = 16.6 Hz), ratio 1.00 : 1.07, proposed to be due to resonance stabilized bridgehead 1-Nb cationic enantiomers in equilibrium with 2-Nb cation. The corresponding 13C proton-coupled NMR spectrum, – 80 o C, has a C3,5,7 triplet, δ 30.45, J(CH) = 139.14 Hz, and C4 doublet, δ 37.7, J(CH) = 154.54 Hz. The C1,2,6 absorption, δ 91.04 is relatively broad, whereas previously at –70 o C, it was a pentuplet. The 13C proton-decoupled spectrum at – 80 o C shows the C4 doublet and C3,5,7 triplet collapsed to a singlet but the C1,2,6 resonance is still broad. Analyses support slowing exchange between resonance stabilized enantiomeric 2-cations at ≤ – 159 o C. Quenching the 2-Nb cation solution with aqueous MeOH at – 66 o C yielded 42.8 % of 1-substituted products (37.7 % 1-hydroxynorbornane, 4.2% 1- chloronorbornane, 0.9 % 1-methoxynorbornane, 43.5% dinorbornylether, 0.4% 2-hydroxynorbornane and 13.3% unidentified products) indicating resonance stabilized 1-Nb cation is indeed present in solution along with the 2-Nb cation. These results complement previous quenching results of 1-chloronorbornane in SbF5-SO2 at – 70 o C which, e.g., after warming to -50 o C yielded 65 % of 1-norbornanol and 0.5 % exo-2-norbornanol. It is crucial to recognize that some previous interpretations of NMR studies at ≤ - 150 o C are not secure. These interpretations did not consider (1) recent evidence indicating anchimeric assistance of 2-exo leaving group displacement by bridgehead hydrogen orbital (2) presence of a pair of stereospecific front-face C1,2,6 hydride shifts via the bridgehead C1 rather than the assumed nonstereospecific 6,2,1 hydride shift for which there is no evidence (3) possibility of C1 instead of C6 carbon bridging, and (4) sigma aromaticity.

1-Norbornyl cation may be in equilibrium with 2-norbornyl cation

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.