MAGNETIC SHIELDING OF SP-HYBRIDIZED CARBONS IN SOME ACETYLENE DERIVATIVES

Principal values of magnetic shielding tensors of acetylenic carbon nu clei for 14 acetylene derivatives have been collected. Apart from some literature data the values for linear monosubstituted acetylenes have been estimated on the basis of appropriate isotropic chemical shifts. For most of the investigated molecules the ab initio GIAO CHF calcula tions of magnetic shielding tensors have been performed and the experi mental and theoretical results have been compared. Even within this li mited class of straightly related structures there is no straightforwa rd relationship between electron charge at a given atom and any of its shielding component, though some qualitative trends do exist. It was shown that substituent electronegativity effect, p-pi conjugation effe ct and heavy atom effect influence first of all the perpendicular comp onent of the shielding tensor of acetylenic carbon nucleus.