TY - JOUR
T1 - Experimental Evidence for the Breakdown of the Karplus Relationship for3J (13C, 1H) in 1H - C - C=13 C Systems
AU - Parella, Teodor
AU - Sánchez-Ferrando, Francisco
AU - Virgili, Albert
PY - 1997/1/1
Y1 - 1997/1/1
N2 - Vicinal 1H, 13C coupling constants were measured for rigid unsaturated 1H-C-C=13C 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 through-space substituent effects also influence the magnitude of the coupling constants in a similar way to that known for saturated systems. In summary, two different additive transmission mechanisms take part in these coupling paths depending on the orientation of the π-system with respect to the allylic bond. The experimental evidence presented demonstrates the breakdown of the Karplus rule in this particular structural fragment.
AB - Vicinal 1H, 13C coupling constants were measured for rigid unsaturated 1H-C-C=13C 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 through-space substituent effects also influence the magnitude of the coupling constants in a similar way to that known for saturated systems. In summary, two different additive transmission mechanisms take part in these coupling paths depending on the orientation of the π-system with respect to the allylic bond. The experimental evidence presented demonstrates the breakdown of the Karplus rule in this particular structural fragment.
KW - 1 H NMR
KW - Allylic systems
KW - Long-range proton-carbon coupling constants
KW - NMR
U2 - 10.1002/(SICI)1097-458X(199701)35:1<30::AID-OMR21>3.0.CO;2-0
DO - 10.1002/(SICI)1097-458X(199701)35:1<30::AID-OMR21>3.0.CO;2-0
M3 - Article
SN - 0749-1581
VL - 35
SP - 30
EP - 34
JO - Magnetic Resonance in Chemistry
JF - Magnetic Resonance in Chemistry
IS - 1
ER -