The 2D Double-Quantum (ZQ) experiment is an example of multiple-quantum spectroscopy. It offers a homonuclear chemical shift correlation 2D map, alternatively to COSY-type experiments.

Easy implementation on any AVANCE spectrometer.

The basic DQ experiment can be obtained by replacing the first 90º 1H pulse of the basic two-pulse COSY sequence by a multiple-quantum preparation period (90º-delay-45º or 90º-delay-135º cluster) (see Homonuclear MQ coherences) ( 82JMR158-48 , 83MOP535 and 83JMR531-51 , and 88JMR241-76 ). In order to avoids undesirable chemical shift evolution, an spin-echo is used. Originally this pulse sequence was intended for the observation of 13C-13C couplings at natural abundance (see 2D INADEQUATE experiment). Modified 2D DQ sequences have been published ( 85JMR67-61 ). Pure-phase DQ spectra can be obtained as proposed in 87JMR493-73 and 90JMR150-88 . 2D Triple-Quantum (TQ) experiment has been reported ( 92MRCS74 ). Improved versions have been proposed using pulsed field-gradients (see ge-2D MQ experiment)

The 2D DQ experiment can be recorded in routine/automation modes. The most important parameter to consider is the delay of the MQ period which is optimized to 1/2JHH in order to obtain anti-phase coherence. The spectral width in F1 must be twice the largest possible DQ frequency.

The 2D matrix contains a series of correlation multiplets centered at the SQ chemical shift in F2 (as in COSY) and at the DQ frequencies (sum of chemical shifts between coupled spins) in F1. Some examples can be found in 88MRC839 , 90JMR150-88 , and 92MRC779 ).

Extensive description of the 2D DQ experiment is found in 88BOOK1 (pages 109-136)

Related experiments:

2D homonuclear experiments

2D gradient-based homonuclear experiments