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C3(SINGLE BOND)M? Bond contribution to polarizability tensor and3J(C1M?) NMR coupling constant in 1-X-3-M-bicyclo[1.1.1]pentanes

✍ Scribed by Giribet, C. G.; de Az�a, M. C. Ruiz; G�mez, S. B.; Botek, E. L.; Contreras, R. H.; Adcock, W.; Della, E. W.; Krstic, A. R.; Lochert, I. J.

Publisher
John Wiley and Sons
Year
1998
Tongue
English
Weight
176 KB
Volume
19
Category
Article
ISSN
0192-8651

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✦ Synopsis

In the present work, the relationship between the large substituent 3 Ž . w x effects on J C H in 1-X-3-M-bicyclo 1.1.1 pentanes, I, and the polarizability of 1 the bridgehead C -M bond is investigated. The existence of such a relationship 3 ␣ is suggested by the finding that the effect of an electronegative substituent X on 3 Ž . Ž . J C M couplings in I M s H is due to a distortion of the C -H bond 1 ␣ 3 toward the C center, which enhances the Fermi contact interaction. If such 1 distortion originates in an electrostatic effect, then in other members of this 3 Ž . series it can be expected that the substituent effects on J C M couplings 1 ␣ should depend strongly on the C -M bond polarizability. Two approaches 3 ␣ are followed. First, the ab initio CLOPPA-IPPP method is applied to study the C -M bond contribution to the molecular static polarizability tensor in I 3 ␣ Ž . M s H, F, CH . Such bond polarizabilities are found to follow the same trend 3 as calculated as well as experimentally determined substituent effects on 3 Ž .

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