Cis coupling constant

Likewise, the vicinal fluorines in l-chloro-l,2-difluoroethenylben-zene (Scheme 2.3) would appear as doublets due to the three-bond F—F coupling between the two fluorine nuclei. Note that the trans coupling constant is much larger (127 Hz) than the respective cis coupling constant (12 Hz). (Note also that the cis-vicinal fluorines deshield each other significantly, relative to the tram-vicinal pair.)... 

The trans, three-bond F—H coupling constant is large and is usually more than double that of the analogous cis coupling constant. 

Compound Solvent 2,3 cis trans 2,4 cis Coupling constants (Hz) 2,5 trans cis trans 3,4 cis trans Ref. 

The same order holds when the vicinal coupling constants are between a proton and fluorine. This is shown in the cis coupling constant 3/HF between -4 and 20 Hz in molecules such as 46, and the corresponding trans coupling constants VHF between 20 and 100 Hz in, for example, 47 and related molecules. 

On Figs. 6, 7 the results for the three-bond 3Jn2-m and 3Jh2-ci coupling constants as functions of the dihedral angle are shown together with the... 

Aryl-27/-azirine-2-(/V-benzyl)carboxamides can be diastereoselectively reduced to the corresponding eu -aziridines using sodium borohydride11. The stereochemistry of the as-aziridines was revealed by H-NMR spectroscopy which showed a cis coupling constant of J2H,3h = 7-8 Hz. 

Randall et al. (34) obtained the chemical shifts and coupling constants for tertiary phosphines in l,3-dialkylimidazolin-2-ylidene carbene complexes. Jz p-M-c(earbene) trms was found to be much larger than the two bond cis coupling constant. In addtion, Jnp-ciZ) in the phosphine ethyl and propyl groups was found to be less than 2.4 Hz which is small when compared to the uncomplexed ligand value of 13 to 15 Hz. 

The rranj-lH-C=C-13c coupling constant of alkenes is always larger than the corresponding cis coupling constant so that an assignment is possible if both isomers are available see [3]. 

Table 7.4 lists some representative three-bond conpling constants. Notice that in the alkenes the trans coupling constant is always larger than the cis coupling constant. Spin-spin coupUng in... 

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