Fluorine chemical shielding tensors and crystal structure of potassium tetrafluorophthalate

Abstract

Chemical structure and reactivity of a silicon single crystal surface fluorinated by xenon fluorideThe 19F shielding tensors of the two aromatic flourines of potassium tetrafluorophthalate (KTFP) are reported. The results indicate that the most shielded elements of the tensors lie perpendicular to the carbon ring in agreement with previous powder studies and, of the two in· plane components, the more shielded is along the CF bond. The results also show that the "ortho effect" of Karplus and Das is not simply additive in the case of KTFP. Such additivity has been assumed by Nehring and Saupe in their liquid crystal study of fluorine shielding tensors in multifluorobenzenes.

Solid-State 19F-NMR Analysis of 19F-Labeled Tryptophan in Gramicidin A in Oriented Membranes

“…The best agreement is seen in column 3, with the ␦ 22 axis pointing along the C-F bond, ␦ 11 lying in-plane of the indole ring, and ␦ 33 aligned perpendicular. This axis assignment is in accordance with similar 19 F CSA tensors that have been described in single crystal studies of fluorobenzenes and other fluorinated aromatic compounds (Snyder, 1965;Nehring and Saupe, 1970;Griffin et al, 1973;Halstead et al, 1975;Mehring, 1983;Hiyama et al, 1986).…”

“…Anisotropic values (but not the alignments) of 19 F chemical shift tensors have been reported for various systems including 5F-Trp, but not yet in the framework of any peptide or protein (Yim and Gilson, 1968;Mehring et al, 1971;Luck et al, 1996). For a few aromatic systems the respective principal tensor axes have been assigned to the molecular frame, but not yet for the indole ring of Trp (Snyder, 1965;Nehring and Saupe, 1970;Griffin et al, 1973;Halstead et al, 1975;Mehring 1983;Hiyama et al, 1986).…”

Determination of the 19F NMR chemical shielding tensor and crystal structure of 5-fluoro-dl-tryptophan

“…Theoretical calculation found a large shielding derivative ($460 ppm/Å ) along the C-F bond [43]. Overall, our 5F-Trp data and other aromatic fluorine results [44][45][46] all suggest this character. Unlike the representative aromatic fluorine compound C 6 F 6 , which is rotating about its six-fold axis rapidly at room temperature [47,48] and yields an axially symmetric chemical shielding tensor [49], 5F-Trp molecules are effectively rigid in the ring plane so tensors r 11 and r 22 are not averaged by motion.…”

Refinement of potassium tetrafluorophthalate, 2K+.C8F4O42−

“…The structure of KTFP was reported by Griffin, Yeung, LaPrade & Waugh (1973). As the aim of that report was primarily for the purpose of determining the 19F chemical shielding tensors, only the molecular structure was described.…”

“…KTFP from TFAC dissolved in aqueous KOH, white prisms, 0.10 x 0.10 x 0.25 mm, Syntex P2~--F diffractometer, l~ittice parameters from 17 reflections (27 < 20 < 56°), data collection: 1661 (h,+_k,+_l with 20 < 115 °, h,k,+l with 115 < 20 < 130 °) automatic recentering every_633_reflections, with 3 standard reflections (002, 210, 031) every 102 reflections (3.1% variation), 874 independent, 836 used in full-matrix least-squares refinement using positional parameters of Griffin et al (1973) Discussion. Refinement in acentric Pc, in which the starting parameters were adjusted so as to destroy initially the twofold symmetry, converged to atomic positions not significantly different from those obtained using the centrosymmetric space group P2/c.…”