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Publisher Summary Developments in nuclear magnetic resonance (NMR) instrumentation combined with the introduction of the Fourier transform (FT) pulse technique allows to measure 13C-13C couplings at natural abundance of 13C isotope. The pulse sequences, such as the one- and two-dimensional incredible natural abundance double quantum transfer experiment (INADEQUATE) technique and its further improvements and/or substitutes, simplify the interpretation of the spectra considerably. This has made 1J (CC) couplings easily accessible even in the case of large molecules. In spite of the initial assumptions, one-bond carbon-carbon couplings undergo strong variations upon substitution and complexation and are, in this way, a sensitive measure of the electronic structure of carbon-carbon bonds. This chapter reviews the factors that determine the 1J (CC) magnitude. Two factors are taken into consideration to estimate the unknown one-bond CC coupling value. These are: (i) hybridization of the bonding orbitals involved and (ii) the ring size of the compound. The electronegativity of the substituents is another important factor that determines the magnitude of one-bond CC couplings. One of the most useful applications of both one- and two-dimensional INADEQUATE experiments concerns the determination of carbon-carbon connectivity of the carbon network. |
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