1. Purpose

Even in these days of high-field NMR spectroscopy, it often happens that proton spectra show higher-order effects because of small chemical shift differences. In these cases a simple change of solvent, especially from chloroform to aromatic solvents (e.g. benzene or pyridine), can cause a dramatic simplification of the spectrum due to a better separation of the signals. This effect is called aromatic solvent-induced shift (ASIS). The effect is usually strong in ¹H NMR spectroscopy but only weak in ¹³C NMR. In this experiment we demonstrate ASIS with ethyl anthranilate.

2. Literature

P. Laszlo, Prog. NMR Spectrosc. 1967, 3, 231–402.
J. Ronayne, D. H. Williams, Annu. Rep. NMR Spectrosc. 1969, 2, 83–124.
F. H. A. Rummens, R. H. Krystynak, J. Am. Chem. Soc. 1972, 94, 6914–6921.
H. Stamm, H. Jäckel, J. Am. Chem. Soc. 1989, 111, 6544–6550.
K. Nikki, Magn. Reson. Chem. 1990, 28, 385–388.

3. Pulse Scheme and Phase Cycle

ASIS experiment pulse sequence and phase cycle

4. Acquisition

Time requirement: 10 min

Sample: 3 % ethyl anthranilate, (a) in CDCl₃ and (b) in [D₆]benzene with 0.1% TMS.

Load standard ¹H NMR acquisition parameters (see Exp. 3.1). Record the spectra of the compound dissolved in both solvents.