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

被引:0
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作者
Mamantov, Andrew [1 ]
机构
[1] US EPA, Washington, DC 20460 USA
关键词
Norbornyl; nonclassical cation; H-1; C-13; NMR; 1-Nb cation; enantiomers; sigma-aromaticity; STABLE CARBONIUM-IONS; NUCLEAR-MAGNETIC-RESONANCE; NONCLASSICAL NORBORNYL CATION; DIELS-ALDER REACTION; PROTONATED NORTRICYCLENE; CARBOCATIONS; SPECTRUM; BOLTZMANN; LUDWIG; STEREOCHEMISTRY; REARRANGEMENTS;
D O I
10.1177/1468678319861319
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
New H-1 and C-13 NMR 400 MHZ spectra of the 2-Nb cation under stable ion conditions, for example, in SbF5/SO2F2/SO2ClF, -80 degrees C, show besides the usual H-1 NMR resonances at delta 4.93, 2.82, 1.85, the never before seen singlet, delta 9.63, and doublet, delta 2.97 (J(2,6) = 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 C-13 proton-coupled NMR spectrum, -80 degrees C, has a C3,5,7 triplet, delta 30.45, J(CH) = 139.14 Hz, and C4 doublet, delta 37.7, J(CH) = 154.54 Hz. The C1,2,6 absorption, delta 91.04 is relatively broad, whereas previously, at -70 degrees C, it was a pentuplet. The C-13 proton-decoupled spectrum at -80 degrees 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 the slowing exchange between resonance stabilized enantiomeric 2-cations at <= -159 degrees C. Some future studies are proposed.
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页数:14
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