Long-Range Coupling Constants

Key Words High-resolution NMR, INADEQUATE, ADEQUATE, Carbon-carbon coupling constants, Long-range couplings, Double-quantum coherence, 13C NMR, 15N NMR, 29Si NMR, 77Se NMR, Fullerenes, Polymers, Review. 

Homonuclear 2D experiment plot of chemical shift vs. chemical shift identifies spin-coupled resonances. Many variations permit measurements of J coupling constants, long-range connectivities, suppression, and enhancement of selected resonances... 

Eor a macromolecule such as a large protein, the steps in characterization involve, first, identification of the spin systems present, using correlated spectroscopy, and identification of neighboring amino acids. The long range noes are then assigned, and three bond coupling constants ate deterrnined. 

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 H and 13CNMR spectra of various cyclopentazepines have been recorded (Tables 1 and 2), as has the HNMR spectrum of 7V,7V-dimethylcyclopent[e]azepin-l-amine.68 A detailed analysis of geminal and long-range 13C-H coupling constants for cyclopent[c]azepine is also available.87 The HNMR spectra of 9//-pyrrolo[l,2-a]azepin-9-one (8b) and its fully delocalized cation have been recorded in various solvents.7... 

The selective heteronuclear /-resolved experiment (Bax, 1984) is used to determine heteronuclear long-range coupling constants via a selecdve n pulse that causes splitting of all carbon signals coupled to that proton. 

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