Inverse halogen dependence in anion 13C NMR

摘要: Halogens cause pronounced and systematic effects on the 13C NMR chemical shift (δ13C) of an adjacent carbon nucleus, usually leading to a decrease in values across halogen series. Although this normal dependence (NHD) is known organic inorganic compounds containing atom its neutral cationic forms, information about carbanions scarce. To understand how δ13C changes molecules with different charges, shielding mechanisms CHX3, CX3+, CX3− (X = Cl, Br, or I) systems are investigated via density functional theory calculations further analyzed by decomposition into contributions natural localized molecular orbitals. An inverse (IHD) determined for anion series as result negative spin–orbit contribution instead scalar paramagnetic effects. The presence nonbonding orbital anions allows magnetic couplings that generate deshielding effect nucleus contradicts classical association between atomic charge.