Revisiting NMR Through-Space J_FF Spin–Spin Coupling Constants for Getting Insight into Proximate F---F Interactions

Abstract

At present times it is usual practice to mark biological compounds replacing an H for an F atom to study, by means of (19)F NMR spectroscopy, aspects such as binding sites and molecular folding features. This interesting methodology could nicely be improved if it is known how proximity interactions on the F atom affect its electronic structure as gauged through high-resolution (19)F NMR spectroscopy. This is the main aim of the present work and, to this end, differently substituted peri-difluoronaphthalenes are chosen as model systems. In such compounds are rationalized some interesting aspects of the diamagnetic and paramagnetic parts of the (19)F nuclear magnetic shielding tensor as well as the transmission mechanisms for the PSO and FC contributions to (4)JF1F8 indirect nuclear spin-spin coupling constants.

Through‐space 19F–19F spin–spin coupling in ortho‐fluoro Z‐azobenzene

“…concluded that lp( σ ) and lp( σ )–lp( σ ) contributions are larger than lp(π) contributions and that TS coupling is maximized for a head‐to‐head orientation of F atoms. Contreras et al . reported that the Fermi contact term is the largest contributor to J FF SSCCs; the second largest is the paramagnetic spin–orbit term.…”

“…[34] Based on computations, Tuttle et al [29] concluded that lp(σ) and lp(σ)-lp(σ) contributions are larger than lp(π) contributions and that TS coupling is maximized for a head-to-head orientation of F atoms. Contreras et al [35] reported that the Fermi contact term is the largest contributor to J FF SSCCs; the second largest is the paramagnetic spin-orbit term. The paramagnetic spinorbit term shows an unsymmetric second rank tensor characterized by the 'geometric effect'.…”

NMR spectral analysis of strongly second‐order 6‐, 8‐, 9‐ and 10‐ spin‐systems (1H─19F, 19F─19F, and 13C─19F) in perfluorotoluyl‐ and tetrafluoro‐pyridyl‐aromatics using the lineshape method ANATOLIA

“…For a series of structurally rigid 1,8‐difluoronaphthalene compounds the through‐space J FF coupling was between 85.2 to 36.6 Hz corresponding to distances of 2.452 to 2.718 Å, with the specific contributions to the measured experimental coupling being dissected, showing that the Fermi contact term of +56 Hz results from a combination of a through‐space coupling (+75 Hz) and σ through‐bond coupling (−19 Hz) . The contributions from the diamagnetic and paramagnetic parts of the 19 F nuclear magnetic shielding tensor, paramagnetic spin‐orbit term and Fermi contact contributions to indirect nuclear spin–spin coupling constants have been rationalised …”

Intriguing Behavior of an Apparently Simple Coupling Promoter Ligand, PPh2(p-C6H4–C6F5), in Their Pd Complexes

“…18 Coupling constants 5 J( 19 F-31 P) are usually very small or unobservable, but exceptions are dicyclohexyl(2',6'-difluoro[1,1'-biphenyl]-2-yl)-phosphine (J F-P = 24 Hz) and L HF . 12 The simplest explanation for these anomalous values is that there is some "through space" coupling contribution to coupling, strongly dependent on the distance between nuclei, 19,20,21 in addition to the 5 J scalar coupling contribution. In the palladium complexes of L HF (see below) this 19 F-31 P coupling is not observed.…”