The selective 1D TOCSY (HOHAHA) experiment has become one of the most important NMR techniques for establishing ¹H-¹H connectivity via scalar coupling in small and medium-size molecules. Magnetization transfer between protons within the same coupling network affords 1D proton subspectra of individual spin systems.  Improved results are obtained from the gradient-based selective ge-1D TOCSY experiment.

Easy implementation on AVANCE spectrometers with selective excitation using shaped pulses.

The selective 1D TOCSY experiment ( 85JACS7197 ) consists of the following parts:

Selective excitationof the selected resonance.

Mixing period to achieve in-phase polarization transfer to other spins. This is usually achieved applying some isotropic mixing sequence like MLEV, WALTZ or DIPSI pulse trains. This in-phase transfer avoids possible cancellation when the coupling is poorly resolved (see MLEV Block and DIPSI-2 Block).

Proton detection as usual.

Several approaches have been reported:

• Selective excitation using a gaussian shape ( 86JMR106-70 ), half-gaussian shape ( 89JMR1-85 ), a DANTE ( 91JACS363 , 92JMR185-96 and 96CONC119 ) and DANTE-z ( 90JMR221-90 and 95JMRA292-117 ) have also been used.
• Generation of pure phase spectra by incorporating a z-filter before acquisition ( 87JMR325-71 ).
• Use of pulsed-field gradients (see  selective ge-1D TOCSY experiment).
• Sensitivity improvement using multiple selective excitation ( 90JMR146-89 and 93JMRA310-105 ).
• Selective TOCSY transfer between J-coupled spins ( 90JMR146-89 ) using selective spin-locking. This idea can be extended by adding consecutive selective spin-lock transfers ( 92JACS10671 , 92JMR208-100 , 93JMRA225-101 , 93JMRA349-103 , 93CPL524 , 94JMRA262-110 , and 95MRC308 ).
• 1D TOCSY experiments can also be applied on overlapped resonances by applying some pseudo-3D experiment as, for instance, the selective 1D NOESY-TOCSY experiment ( 94JMRB289-104 ).

The selective 1D TOCSY experiment can be run with minor changes from a predefined parameter set. Detailed description of the experiment can be found in the original publication ( 86JMR106-70 ). Two important parameters to consider are:

Selectivity of the selective excitation pulse: the user must define the shape, the duration and the power level needed for a defined excitation profile.

Optimization of the mixing period (as a function of 1/(J(HH)). When long mixing times are employed, magnetization is transferred to the whole spin subsystem, similar to the multiple-step RELAY experiment.

For further details on practical implementation of selective 1D TOCSY experiments on AVANCE spectrometers see Tutorial: selective 1D TOCSY experiment.

In 1D TOCSY spectra, only protons belonging to the same spin subsytem appear as in-phase multiplets. The use of gradients allows to obtain a clean, artefact-free spectrum in a short time from which careful analysis of the multiplets can be done.

An excellent review describing selective excitation in 1D and multidimensional NMR experiments was published ( 91MRC527 ).

The selective 1D TOCSY experiment can be the starting block of more sophisticated pseudo-3D experiments as:

• Selective 1D TOCSY-COSY experiment ( 89JMR186-81 ).
• Selective 1D TOCSY-TOCSY experiment ( 90JMR199-86 ).
• Selective 1D TOCSY-NOESY experiment  ( 90JMR221-90 , 92JMR185-96 , 93JMRB107-102 , and 94JMRB289-104 ).
• Selective 1D TOCSY-ROESY experiment  ( 92JMR185-96 , 93JMRB107-102 , and 95JMRB186-107 ).
• Selective 1D TOCSY-INEPT experiment ( 92JMR178-99 , and 93MRC403 ).