Conformational Analysis of 3-(Trimethylsilyl)propionic Acid by NMR Spectroscopy: An Unusual Expression of the β-Silyl Effect

Abstract

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_2CH_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 -(trimethylsilyl)ethanesulfonate anion were also conducted to compare the relative structural influences on the conformational preferences of silicon and carbon.