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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 14, Number 5
BKCSDE 14(5)
May 20, 1993 

13C-1H Coupling Constant as a Criterion for the Presence of π Bridging in Substituted 9-Benzonorbornenyl Cation
Gweon-Young Ryu, Jung-Hyu Shin*
The discrete structure of substituted 9-benzonorbornenyl cation 3a and 3c was studied using the empirical △J equation which was developed by Kelly and coworker. The △J values of substituted 9-benzonorbornenyl cations were obtained from p-methyl-6,7-dimethyl benzonorbornen-9-yl (3a) and 9-methyl-6,7-dimethyl benzonorbonen-9-yl (3c) cations under stable ion conditions, and were compared with those of the corresponding ketone analog; these cations were generated by dissolving the corresponding carbinols in superacid at -120℃ and the nmr spectra taken at -60℃∼-90℃. The △J values are 8.7 Hz for the bridgehead carbons in cation 3c and 3.1 Hz for cation 3b. The △J values at C5,8 in fused benzene ring are 14.3 Hz for cation 3c and 8.7 Hz for cation 3a. The excellent correlation of the △J values with 19F chemical shifts of p-fluorophenyl-6,7-dimethylbenzonorbornenyl cation (3d) indicate that △J value is a reliable probe to charge density at adjacent cationic carbon. These NMR parameters strongly support that the symmetrically π-bridged nonclassical structure (type 2) of substituted 9-benzonorbornenyl cations in stable ion conditions.
546 - 548
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