Hydrogen-carbon spin coupling constants

Table 7.56 One-Bond Carbon-Hydrogen Spin Coupling Constants 7.107...

Murata, M. et al., Absolute configuration of amphidinol 3, the first complete structure determination from amphidinol homologues Application of a new configuration analysis based on carbon-hydrogen spin-coupling constants, J. Am. Chem. Soc., 121, 870, 1999. 

Carbon-hydrogen spin-spin coupling constants are included in a review by Hansen and discussed in terms of ring strain, steric effects, electronegativity, lone pair effects and electric field effects. Additivity of these effects in a few systems is commented on. 

Resonance structure b is commonly used to describe delocalization of tt electrons in butadiene. Resonance structures c and d describe hyperconjugation. The structures represent electron transfer between anti hydrogens by ct-ct interactions. Note that the hydrogen atoms act as both electron donors and acceptors. As the two hydrogens are in very similar chemical environments, we expect littie net transfer of charge, but the delocalization affects such properties as NMR spin coupling constants. We will see in Topic 1.1 that this kind of delocalization is also important for hydrogens bonded to sp carbon atoms. 

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