Long-range 13C-’H couplings

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... 

In most cases, the stereochemistry of the quaternary carbon atom in branched-chain carbohydrates cannot be elucidated from H-n.m.r. spectra, but 13C-chemical shifts, or long-range, 13C- H coupling-constants, may often yield valuable information.114-118 Likewise, the stereochemistry of acetal carbon atoms of benzylidene derivatives,103, 104 and of acetals derived from pyruvic acid,105,106 may be determined from l3C-chemical shifts. 

Table 16 Long Range 13C, H NMR Coupling Constants in Simple Furan Derivatives ...

In 13C NMR spectra this means the appearance of the carbon signal acquired without decoupling and under low resolution so that long-range C-H couplings can be ignored. 

Aside from the initial applications of the n, 1- and m,n-ADEQUATE experiments in the elucidation of the structure of 5,6-dihydrolamellarin (3, see Sections 4.1, 5.1 and 6.5), the author is unaware of any reported applications of these experiments in the literature.38 Given the potential ambiguities associated with the two long-range magnetization transfer steps of the latter, coupled with the very low sensitivity and the fact that correlations are observed in Fi at the DQ frequency of the coupled carbons rather than at the 13C shift as in the 1,1- or 1,h-ADEQUATE experiments, it is probably quite likely that the m,n-ADEQUATE experiment will continue to be very sparingly utilized for structure elucidation. 

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