A PROPOSED STANDARD SAMPLE FOR NUCLEAR OVERHAUSER EFFECT MEASUREMENTS

A standard sample for the measurement of proton-proton nuclear Overhau ser effects (NOE) is proposed. 1,5-Dichloro-2,4-dimethoxybenzene (DCDM B) shows an essentially full (50%) enhancement of the proton H-3 when the protons of the flanking methoxyl groups are saturated. The molecul e is appropriate as a standard for the following reasons. The molecule is stable and easily synthesized. All the lines in the spectrum appea r as singlets, so selective population transfer effects cannot obscure the NOE. The proton at position 6 provides a monitor of other relaxat ion mechanisms that would reduce the NOE. The NOE was verified by two complementary experiments. One is the standard technique of measuring the intensity with and without irradiation. A second method, based on spin-lattice relaxation rate experiments, provides unbiased data and g ives an statistical estimate of the errors. Within experimental error, the NOE for DCDMB is 50%. (C) 1998 John Wiley & Sons, Ltd.