Coupling vicinal

Figure 13 20 there are two other vinylic protons Assuming that the coupling constant between the two geminal protons in ArCH=CH2 is 2 Hz and the vicinal coupling constants are 12 Hz (cis) and 16 Hz (trans) describe the splitting pattern for each of these other two vinylic hydrogens... 

Spm-spm splitting of NMR signals results from coupling of the nuclear spins that are separated by two bonds (geminal coupling) or three bonds vicinal coupling)... 

Vicinal coupling constants Jhh indicate very clearly the relative configuration of the coupling protons. Their contribution depends, according to the Karplus-Conroy equation... 

Vicinal coupling (Section 13.7) Coupling of the nuclear spins of atoms X and Y on adjacent atoms as in X—A—B—Y. Vicinal coupling is the most common cause of spin-spin splitting in FI NMR spectroscopy. 

It is now generally realized that the angular dependence of vicinal coupling constants is considerably mare complex than was at first appreciated (24, 38, 39) and that care must be exercised in utilizing... 

In view of the possible ambiguities which can attend conformational assignments based on vicinal coupling constants, it is fortunate that both long-range and geminal couplings each exhibit stereospecific dependences. 

The SECSY spectrum of the coumarin presents cross-peaks for various coupled nuclei. These cross-peaks appear on diagonal lines that are parallel to one another. By reading the chemical shifts at such connected cross-peaks we arrive at the chemical shifts of the coupled nuclei. For instance, cross-peaks A and A exhibit connectivity between the vinylic C-4 and C-3 protons resonating at 8 7.8 and 6.2, respectively. The C-4 methine appears downfield due to its )3-disposition to the lactone carbonyl. Similarly, cross-peaks B and B show vicinal coupling between the C-5 and C-6 methine protons (8 7.6 and 7.1, respectively) of the aromatic moiety. The signals C and C represent the correlation between the oxygen-bearing C-11 (85.4) andC-12 (84.6) methine protons in the side chain. These interactions are presented around the structure. 

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