Thomas R. Hoye and Hongyu Zhao, "A Method for Easily Determining Coupling Constant Values: An Addendum to "A Practical Guide to First-Order Multiplet Analysis in 1H NMR Spectroscopy," J. Org. Chem., 2002, 67, 4014-4016. Web copy
Antony Williams, Sergey Golotvin, Eugene Vodopianov, "J-Coupler - A Tool for Automated First Order Multiplet Analysis," March 11- 16, 2001. Orlando, Florida, USA, 42nd ENC, J-coupler [pdf]
Spin-Spin Coupling Constant Interpretation
Spin-spin coupling constants depend on the dihedral angle bewteen the coupled spins.
The 3J vicinal alkyl coupling constants are approximated by the
3J = 7.8 - 1.0 cos(phi) + 5.6 cos(2*phi)
The Altona equations are more accurate. Please see: C. A. G. Haasnoot, F. A. A. M. DeLeeuw and C. Altona, "The Relationship Between Proton-Proton Coupling Constants and Substituent Electronegativities-I," Tetrahedron, 1981, 36(19), 2783-2792.
The 3J vinyl and 4J allylic coupling constants
are estimated by the modified
|3J = 6.6 cos2(phi) + 2.6 sin2(phi)||(0o<= phi <= 90o)|
|3J = 11.6 cos2(phi) + 2.6 sin2(phi)||(90o<= phi <= 180o)|
|4J = 1.3 cos2(phi) - 2.6 sin2(phi)||(0o<= phi <= 90o)|
|4J = - 2.6 sin2(phi)||(90o<= phi <= 180o)|
For the other coupling types, typical values are listed in Table 3.26i, 3.27, and 3.29 in D. H. Williams, I. Fleming, "Spectroscopic Methods in Organic Chemistry,4th ed.," McGraw-Hill, London, 1987. pp 143-146. For more exact calculations, including second order effects please see JD: Spin-Spin Splitting Simulation
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