Local anisotropic contributions to 1H nuclear magnetic resonance shifts in alkynes

Local anisotropic contributions to chemical shifts of protons sited near an alkyne moiety have been calculated using a classical model previously applied to aromatic systems. The results are presented in terms of an isoshielding contour map. The upfield shifts of ethyne and propyne and also the downfield shifts of the γ-protons of cyclooctynes are well accounted for by this theory.