Four-bond W couplings

W-coupling. A four-bond J-coupling occurring when two NMR-active spins are separated by four bonds held in a static, planar conformation that forms the letter "W". 

H—H couplings of 1 Hz or more through four single bonds have been observed almost exclusively in systems of the sort in which the four bonds are in a planar W conformation (II). 

Ideally, a given substructure corresponds to an ideal ISNet (such as supposing every geminal/vicinal proton coupling pair can be observed). See Fig. 3 for the ideal ISNets of Lys and Val. Four-bond coupling may be observed from a double bond or a W conformation of four a bonds in a ring system. ... 

W formation coupling A four bond coupling observed in the NMR spectrum, i.e. 4J, e g. between meta hydrogens in an aromatic ring. 

The 1H COSY spectrum of isotatic PMMA enables unambiguous assignment of erythro and threo methylene protons based on the fact that only the erythro proton is capable of forming with a-methyl protons a W -shaped four-bond path of long-range coupling.203 Tetrad-pentad correlation was also observed in the 1H COSY spectrum of radically prepared PMMA.203... 

X = SMe are imexceptional, for X = SOMe and X = S02Me axial X is more stable than equatorial X. The suggested reason is that dipolar interactions of the type (11) could be responsible. In support of this idea, a four-bond coupling of 1.14 Hz between the 5-methyl and the C-5 H is observed. The W plan required for this coupling is only compatible with an endocyclic methyl group. 

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