The parameters of the 13C NMR spectra of substituted acetylenes: relation with electronic structure and reactivity

Questions concerning the electronic structure of the ethynyl fragment and the effectiveness of its interaction with various heteroatomic and unsaturated substituents are examined on the basis of the analysis of an extensive set of parameters of the ¹³C NMR spectra of mono- and di-substituted acetylenes. The additive influence of the two substituents in disubstituted acetylenes on the shielding of the sp-carbon atoms, due to the counterpolarisation of the orthogonal π-systems of the triple bond, is demonstrated. The question of the possible use of the ¹³C NMR spectral parameters for the estimation of the reactivity of the triple bond is discussed.
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