180º pulses placed into heteronuclear pulse sequences can be used to refocus a desired chemical-shift, homo- or heteronuclear J-coupling information, depending of the position into the pulse sequence and on the nuclei that they are applied.

If a single refocusing 180º pulse is applied on ¹H nuclei, ¹H chemical shift and ¹H-¹³C coupling constants are refocused at the end of the echo period while ¹³C chemical shift and ¹H-¹H coupling constants are not affected.

An example is the variable evolution period of the 2D HMQC experiment. In the case  of the 2D HSQC experiment, ¹H nuclei does not evolve during the variable evolution period and, therefore, ¹H-¹H coupling constants don't appear (only appears ¹³C chemical shift) in the F₁ dimension of this  spectrum.

Easy implementation on AVANCE spectrometers.

There are 32 duration parameters, d0-d31,  to be specified in seconds. They are executed as delays without any further actions by the pulse program commands d0. They can be incremented or decremented using the pulse program commands id0-id31 or dd0-dd31, respectively. The changes are given by the parameters IN0-IN31. The pulse program commands rd0-rd31 reset a respective delay to its original value. The delays may also be changed by means of arithmetic expressions during pulse program execution.

The most standard way to implement the variable ¹H-decoupled X-evolution t₁ period in a ¹H-detected experiment is:

... d0 (p2 ph1) d0 ...

in which:

• d0 is the incremented delay (in seconds).
• p2 is the 180º ¹H pulse (in microseconds) applied at a power level pl1 from the f1 channel.
• ph1 is the phase specified at the end of pulse program.

It is also possible to decouple more than one heteronuclear coupling: