180º pulses placed into heteronuclear pulse sequences can be used to refocuse 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.

A particular case of this example should be the variable ¹H-decoupled X-evolution t₁ period.

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 standard way to implement a ¹H-decoupled X-evolution period in a ¹H-detected experiment is:

... d2 (p2 ph1) d2 ...

in which:

• d2 is the evolution 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.

For a X-detected experiment should be:

... d2 (p4 ph1):f2 d2 ...