Carbon-13 chemical shift tensors for acylium ions: A combined solid state NMR and ab initio molecular orbital study
- Texas A&M Univ., College Station, TX (United States)
- Pacific Northwest National Lab., Richland, WA (United States)
We report the principal components of the {sup 13}C chemical shift tensors for seven acylium ions, determined by both slow speed magic angle spinning (MAS) nuclear magnetic resonance (NMR) and theoretical methods. Experimentally, the acylium ions were prepared either by direct reaction of the parent acyl halides with metal halide powders, including frozen antimony pentafluoride, or by the reaction of alkyl halides with carbon monoxide on aluminum chloride (AlCl{sub 3}). The generalization of our recent observation of the acetylium ion on AlCl{sub 3} to other cations is direct proof of free acylium ion intermediates in Friedel-Craft acylation reactions. {sup 13}C CP MAS NMR spectra of the acylium ions were acquired at temperatures ranging from 83 to 298 K, and the principal components of the {sup 13}C chemical shift tensors were extracted by fitting the side band intensities of the MAS spectra. With the exception of the chloroacetylium ion, the acylium ions studied have isotropic {sup 13}C{sub 1} chemical shifts of 154 {+-} 1 ppm, but clear variations in the principal components of the shift tensors were measured. We optimized the geometries of the acylium ions using second-order Moller-Plesset perturbation theory (MP2) and the 6-311G{sup *} basis set. The results of analysis of the MP2 wave functions help answer long standing questions regarding the structure and bonding of acylium cations. 76 refs., 7 figs., 4 tabs.
- DOE Contract Number:
- FG03-93ER14354
- OSTI ID:
- 459479
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 2 Vol. 119; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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