1. Purpose

The basic HMQC sequence as described in Experiment 10.13 gives rather poor signal suppression for protons bonded to ¹³C or ¹⁴N. A considerable improvement can be achieved by using the BIRD sandwich (see Exp. 10.14) prior to the HMQC sequence. Furthermore, the use of an additional purging scheme with a spin-lock (see Exp. 6.17) reduces unwanted signals nearly to the level obtainable using pulsed field gradients (see Exp. 12.4) and allows the use of a higher receiver gain. Since this technique can be performed on older instruments not equipped with a field gradient unit, it was termed PMG (Poor Man's Gradient) [2]. Here we show a phase-sensitive version with ¹³C-GARP decoupling using ethyl crotonate. The method shown currently seems to be the best for routine H,C-correlation under the above-mentioned instrumental restrictions. The basic idea has now also been applied within the HSQC and HMBC pulse techniques [3].

2. Literature

G. Otting, K. Wüthrich, J. Magn. Reson. 1988, 76, 569-574.
J.-M. Nuzillard, G. Gasmi, J.-M. Bernassau, J. Magn. Reson. Ser. A 1993, 104, 83-87.
G. Gasmi, G. Massiot, J.-M. Nuzillard, Magn. Reson. Chem. 1996, 34, 185-190.

3. Pulse Scheme and Phase Cycle

Poor Man's Gradient HMQC pulse sequence with GARP decoupling

4. Acquisition

Time requirement: 10 min

Sample: 5% ethyl crotonate in CDCl₃.