The shielding effect of heterosubstituents in 13C nuclear magnetic resonance

Abstract

The effect of a heterosubstituent X on 13C chemical shifts, in conformations characterized by dihedral angles of 60°, is analyzed in terms of α-shifts, heteroatom–carbon (XC), hydrogen–heteroatom (HX) and carbon–heteroatom (CX) gauche interactions, and nonbonded γ(X) and δ(X) interactions. The more general parameters [Formula: see text] describe the β-heteroatom shifts in conformations in which the dihedral angles [Formula: see text] differ from 60°. The shielding effects of chlorine, exocyclic oxygen, and endocyclic nitrogen are analyzed.