Experimental determination of the nuclear Overhauser effect

Abstract

Discusses procedures used to obtain experimental intramolecular nuclear Overhauser effect (NOE) enhancements on commercial student spectrometers.

Conjugate addition of trimethysilyllithium. A preparation of 3-silyl ketones

“…The regiochemistry of the alkylation follows from mechanistic considerations and from the observation of a 12% NOE enhancement of the trimethylsilyl grouping (relative to tetramethylsilane) on irradiation of the 2-methyl signal in the NMR. 12 The equatorial nature of the methyl group (and therefore the trans disposition of the two substituents) is indicated by the stability of 4 to epimerizing conditions (NaOMe, MeOH, 1 hr, 25 °C) and by a half-height peak width for each member of the methyl doublet which is only 0.3 hertz broader than tetramethylsilane. 13 Reaction of the intermediate enolate with less reactive halides (e.g., npropyl iodide) gives rise to complex mixtures.…”

Nuclear magnetic resonance spectrometry

“…Reports of the intermolecular nuclear Overhauser effect (576,577), influence of paramagnetic species on the internuclear Overhauser effect (578), determination of nuclear Overhauser enhancement factors from NMR spinlattice relaxation rates (579), the Overhauser effect in a weak or quasinull field (580) as well as quantitive application of the determination of molecular structure (581) are available. An experiment suitable for demonstration of the nuclear Overhauser effect at the undergraduate level has been described (582).…”