Ab Initio/IGLO/GIAO-MP2 Studies of Fluorocarbocations:  Experimental and Theoretical Investigation of the Cleavage Reaction of Trifluoroacetic Acid in Superacids^1a

Abstract

The structures of a number of fluorocarbocations were calculated at the correlated MP2/6-31G* level. 13C and 19F NMR chemical shifts of fluorocarbocations were calculated for the first time using IGLO and GIAO-MP2 methods. The data showed good correlation of calculated 19F and 13C NMR chemical shifts with the experimental chemical shifts of fluorocarbocations. The correlation for GIAO-MP2-calculated 19F NMR chemical shifts with the experimental data is excellent. Using theoretical calculations as guidance, the protolytic cleavage of trifluoroacetic acid (CF3COOH) in superacids forming CF4 was also investigated experimentally and by ab initio calculations. This reaction is suggested to involve the gitonic CF3C(OH)(OH2)2+ dication as an intermediate.

First Detection of a Selenenyl Fluoride ArSeF by NMR Spectroscopy: The Nature of Ar2Se2/XeF2 and ArSeSiMe3/XeF2 Reagents

“…GIAO‐MP2 and GIAO‐B3 LYP calculations : GIAO calculations of the magnetic shielding constants are helpful for the prediction and interpretation of NMR chemical shifts, also for 19 F and 77 Se NMR data 54–60. We have calculated the 77 Se and 19 F chemical shifts of the species discussed to secure the chosen assignments of the experimental spectra.…”

Comparison of different theory models and basis sets in the calculation of13C NMR chemical shifts of natural products

“…calculations are 31 P, 15 N, 1 H, 17 O and 13 C. Owing to the intrinsic feature of the 13 C chemical shift, which is spread over a wide spectral window, its calculation has proved to be particularly valuable as a support in the structural analysis of organic compounds. In detail, this approach has been employed to investigate reaction mechanisms, 3,4 unstable ions, 5,6 organometallic complexes, 7,8 tautomerism, 9,10 conformational properties 11,12 and, in general, different structural aspects 13 -15 of organic molecules. The gauge-including atomic orbital (GIAO) 16,17 method is one of the most common approaches for calculating nuclear magnetic shielding tensors.…”

Fluorophenoxycarbene inside a Hemicarcerand: A Bottled Singlet Carbene

“…More importantly, they observed excellent linear correlations between measured and computed δ F and δ C values. We were delighted to find similar correlations when we compared the experimentally derived chemical shifts of C 6 H 5 F, CH 3 F, 1,3‐dimethylimidazolidin‐2‐ylidene,4b 1,3‐dimethylimidazol‐2‐ylidene,4b 1‐fluoro‐1‐cyclopentyl cation,13 1‐fluoro‐1‐cyclopropyl cation,16 and 2‐fluoro‐2‐propyl cation16 with those computed at the PBE1PBE/6‐311++G(2d,p) level (see the Supporting Information). These experimentally derived values were then used to correct the δ F and δ C values reported in Table 1: ${\delta {{{\rm corr}\hfill \atop {\rm F}\hfill}}}$ ( 1 a )=159.2, ${\delta {{{\rm corr}\hfill \atop {\rm F}\hfill}}}$ ( 1 b )=141.1, ${\delta {{{\rm corr}\hfill \atop {\rm C}\hfill}}}$ ( 1 a )=290.0, and ${\delta {{{\rm corr}\hfill \atop {\rm C}\hfill}}}$ ( 1 b )=301.4 ppm.…”