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Conformational analysis of 3-(trimethylsilyl)propionic acid by NMR spectroscopy: an unusual expression of the beta-silyl effect.

Nkansah RA, Gerken JB, Roberts JD

Crellin Laboratory of Chemistry, California Institute of Technology, Pasadena, California 91125, USA.

The rotational freedom of the carbon-carbon single bonds of 1,2-disubstituted ethanes affords the possibility of these compounds existing as a rapidly interconverting mixture of conformers in solution. The conformational preferences of one such compound, 3-(trimethylsilyl)propionic acid, and its anion were studied in water, dimethyl sulfoxide, methanol, ethanol, isopropyl alcohol, tert-butyl alcohol, tetrahydrofuran, and toluene with 1H NMR spectroscopy. The conformational preferences were determined from the vicinal proton-proton coupling constants between the hydrogen nuclei of the CH(2)CH(2) group with the aid of the Altona equations to derive the equilibrium anti and gauche percentages of rotamers from the averaged NMR-time scale couplings. Conformational analyses of 4,4-dimethylpentanoic acid and its anion as well as 2-(trimethylsilyl)ethanesulfonate anion were also conducted to compare the relative structural influences on the conformational preferences of silicon and carbon.

Published 24 August 2007 in J Org Chem, 72(18): 6956-60.
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