The TANGO cluster ( 84JMR348-58 ) is a group of pulses that permit discrimination on the basis of the size of proton-carbon (J_CH) coupling constants. Differentiation is based on the fact that the ¹J_CH values are in the range from 125-220 Hz while ⁿJ_CH values are generally less than 15 Hz. There are basically two alternatives:

• All protons directly bonded are excited while protons long-range coupled are unaffected.
 
• The protons long-range coupled are excited and the direclty-bonded are inverted.

The difference between these two versions of the TANGO cluster lies in the manipulation of the direct components relative to the long-range components of magnetization by means of the proton pulse lengths and their phases. the TANGO cluster has been used as a building block in both preparation and evolution periods.

Applications:

• Suppression of ¹²C-attached protons using a TANGO-gradient block in a 3D HCPCH experiment.

Easy implementation on AVANCE spectrometers.

The standard way to implement a TANGO cluster is:

... (p3*1.5 ph1):f2 d2 (p3*2 ph2):f2 (p2 ph4) d2 (p3*0.5 ph3):f2 ...

in which p3 is the 90 degree decoupler 1H pulses, p2 is the 180 degree transmitter 13C pulse, d2 is the delay optimized to 1/(2J(XH)) and all the phases are set to x.