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 ¹³C nuclei. In this case, ¹³C chemical shift and ¹H-¹³C coupling constants are refocused at the end of the period while ¹H chemical shift  and ¹H-¹H coupling constants are not affected.

An example is the evolution period in the 2D HETCOR  experiment.

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 the variable X-decoupled ¹H-evolution t₁ period in a X-detected experiment is:

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

in which:

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

On the other hand, in a ¹H-detected experiment should be as:

... d0 (p4 ph1):f2 d0 ...

in which:

• d0 is the incremented delay (in seconds).
• p4 is the 180º X pulse (in microseconds) applied at a power level pl2 from the f2 channel.
• ph1 is the phase specified at the end of pulse program.