β-Carbon Shielding Effects in Carbon-13 Nuclear Magnetic Resonance Spectroscopy

Abstract

Carbon-13 chemical shifts in saturated hydrocarbons of staggered conformation may be derived from the corresponding resonances in ethane, propane, isobutane, and neopentane in the following way: every H—C—C(α)—C(β) gauche interaction between an α-hydrogen and a 3-carbon deshields a carbon nucleus by ca. 4.7 p.p.m. Every exocyclic carbon–carbon gauche configuration H—C(α)—C—C(α)—C(β)—H has a deshielding effect of ca. 1.7 p.p.m., as the result of nonbonded hydrogen–hydrogen γ-interactions. Every nonbonded interaction between an α-hydrogen and a hydrogen on a γ-carbon makes a shielding contribution of ca.−4.5 p.p.m.