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

Abstract

One-bond spin–spin coupling constant (SSCC) data may be useful in providing information on the stereochemistry and intramolecular interactions in molecules.

Anomeric and Perlin Effect Ladders for 2-Substituted 2-Fluorotetrahydro-2H-pyrans Using Sensitive Structural, Energetic, and NMR Probes

“…Similarly, in the normal Perlin effect correlations of the Δ R (C–F) ax‑eq indicator increase (positive values) the Δ­( 1 J C–F ) ax‑eq indicator in the opposite direction. These correlations manifest the stereoelectronic origin of the normal and reverse Perlin effects composed of three energy componentssteric, hyperconjugative, and electrostaticadvanced by Freitas and co-workers. ,, …”

“…In contrast for hypohalides and amino substituents, the normal Perlin effect (|( 1 J C–F ) eq | > |( 1 J C–F ) ax |) observed by Perlin and Casu is observed. The normal and reverse Perlin effects have been extensively studied in fluorinated six-membered rings, ,,,,− but their origin remains debatable. Freitas’s group ,, thoroughly investigated the factors tuning the fluorine Perlin-like effects in 2-fuoro­tetrahydropyran and 2-, 3-, and 4-fluoro-substituted piperidine derivatives and provided a general interpretation based predominantly on dipolar and not hyperconjugative interactions.…”

“…In 1969, Perlin and Casu observed that the magnitude of the 1 J C–H coupling constants of the equatorial proton is larger (by 8–10 Hz) with respect to those of the axial proton, ( 1 J C–H ) eq > ( 1 J C–H ) ax . The stereoelectronic effects on 1 J C–H coupling constants have been termed Perlin effects, and they were extensively investigated by Perlin and his co-workers and many other research groups. − The one-bond 1 J C–H coupling constant in pyranosyl rings was employed as a reliable indicator of the stereochemistry at the anomeric center . However, the opposite sequence of 1 J C–H coupling constants was observed by Bailey et al and Juaristi and co-workers − in a number of 1,3-dithianes, and it was concluded that factors other than n → σ* stereoelectronic interactions are also responsible for the Perlin effect.…”

“…These correlations manifest the stereoelectronic origin of the normal and reverse Perlin effects composed of three energy componentssteric, hyperconjugative, and electrostaticadvanced by Freitas and co-workers. 19,21,27 In the linear plots of the Δ( 1 J C−F ) ax-eq vs ΔG ax-eq , Δ( 1 J C−F ) ax-eq vs ΔE(2) ax-eq , and Δ( 1 J C−F ) ax-eq vs ΔΔE deloc correlations (Figure S16), the substituents cluster into four groups. The clustering of substituents into smaller groups may be due to the different electronic features of substituents and the different sensitivity of the Perlin effect toward the steric, hyperconjugative, and electrostatic interactions responsible for the normal and reverse Perlin effects.…”

Robust fluorine effects on molecular conformations of 2-amino-2-fluorotetrahydro-2H-pyrans: fluorine-Perlin-like vs. Perlin effects

“…As far as we know studies on the conformational behavior of fluorinated tetrahydropyran rings to understand the stereoelectronic influences of fluorine on molecular conformations are limited, [10][11][12][13][14][15][16][17][18][19] relative to the rich literature concerning the studies on fluorine effects in tuning the electronic profiles in medicinal and bioorganic chemistry. 20,21 Xu et al 10 showed that it is possible to restore the exo-anomeric effect of an acetal or natural sugar when replacing one of the oxygen atoms at the endocyclic position by a CF 2 group.…”