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Experimental Evidence for the Breakdown of the Karplus Relationship for 3J(13C, 1H) in 1H—C—C=13C Systems

✍ Scribed by Teodor Parella; Francisco Sánchez-Ferrando; Albert Virgili

Publisher
John Wiley and Sons
Year
1997
Tongue
English
Weight
249 KB
Volume
35
Category
Article
ISSN
0749-1581

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✦ Synopsis

Vicinal 1H, 13C coupling constants were measured for rigid unsaturated 1HÈCÈCx13C molecular frameworks at natural abundance. As a general trend, an empirical range of 4.5-6.5 Hz is observed independent of the value of the dihedral angle between the CH bond and the plane of the double bond. Furthermore, through-bond and throughspace substituent e †ects also inÑuence the magnitude of the coupling constants in a similar way to that known for saturated systems. In summary, two di †erent additive transmission mechanisms take part in these coupling paths depending on the orientation of the p-system with respect to the allylic bond. The experimental evidence presented demonstrates the breakdown of the Karplus rule in this particular structural fragment.

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