Does induced current density explain the C–H and C–F Perlin effects?

Abstract

Spin–spin coupling constant (SSCC) data may be useful in providing information on the stereochemistry and intramolecular interactions in molecules. One-bond C–H and C–F SSCCs (¹J_CH and ¹J_CF) are amongst the most important NMR parameters used to study the structure of alicyclic six-membered rings, because the Perlin effect, defined as ¹J_CHeq > ¹J_CHax, and the fluorine Perlin-like effect, defined as |¹J_CFeq| > |¹J_CFax|, are in wide currency to probe the conformations of these compounds. The origin of these effects has been usually attributed either to dipolar interactions or hyperconjugation, while the induced current density (ICD) has been recently correlated to the magnetic shielding tensors in some six-membered ring compounds, and then used to explain the Perlin effect. Accordingly, this work reports an analysis of the ICD as a descriptor of ¹J_CH and ¹J_CF in a series of six-membered rings to find out the role of the ICD in the conventional and fluorine Perlin effect. The atoms in molecules (AIM) magnetic responses obtained from density functional theory (DFT) calculations for the studied compounds did not show any relationship of the first-order electronic current density (ΔJ⁽¹⁾) with the calculated Δ¹J_CHax-eq and Δ¹J_CFax-eq values. Consequently, the title effects cannot be precisely explained by ICD. Nevertheless, an interesting relationship between ΔJ⁽¹⁾ and Δdelocalization involving σ_CH* orbitals is observed.