Longer-range couplings

J, V, V, V nuclear spin-spin coupling constant (in Hz) through two, three, four and five bonds (geminal, vicinal, longer-range couplings)... 

As indicated earlier, vicinal F—F coupling constants in perfluoroal-kanes are often very small, virtually negligible in comparison to longer-range couplings, as is the case for peril uoro-n-pcntanc above where the four-bond F—F coupling is 10.2 Hz. 

A longer-range coupling has been detected in 140, between the ringed hydrogen atoms, and the stereospecificity used to assign the conformation. (1988,117)... 

Table 3.13(b). One-Bond and Longer-Range Couplings and 2JCX, 3JCX, 4JCX, of Selected Phenyl Derivatives X(C6HS) Data from Ref. [142],... 

Allylic and longer-range couplings are not always observed. For example, in a range of 3-acyl-4-phenyl-5-trifluoro-methyl-2//-thiopyrans, H-4 and H-2 each appear as a singlet resonating at ca. 7.0 and 3.6 ppm, respectively <1995JFC(70)121>. 

Several techniques have been developed that enable the number of hydrogens attached to the carbon to be determined. An older technique, called off-resonance decoupling, allows hydrogens and carbons that are directly bonded to couple but removes any longer-range coupling. In an off-resonance decoupled spectrum, a CH3 appears as... 

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