The INADEQUATE (Incredible Natural Abundance Double Quantum Tranfer Experiment) experiment permits to obtain information derived from ¹³C-¹³C couplings and can be used to establish the identity of adjacent carbon atoms in a molecule. In addition, from INADEQUATE spectra, direct and long-range¹³C-¹³C coupling constants can be measured.

Easy implementation on AVANCE spectrometer. However, the signals due to ¹³C-¹³C couplings are 1/200 the intensity of the signal from a single ¹³C. For this reason, the INADEQUATE experiment has a very low sensitivity and high sample concentrations are usually required

The basic INADEQUATE pulse sequence ( 80JACS4849 ) consists of the following steps (see creation of homonuclear MQ coherences):

• Relaxation period (d1) to achieve a pre-equilibrium state for the ¹³C nuclei.
• 90º ¹³C pulse to create transverse ¹³C magnetization.
• An evolution delay optimized to 1/2*J(CC) to achieve antiphase ¹³C magnetization. A 180º ¹³C pulse is applied at the middle of this period in order to refocus ¹³C chemical shift while ¹³C-¹³C are not affected.
• A second 90º ¹³C pulse to create multiple-quantum (MQ) ¹³C magnetization.
• A third 90º ¹³C pulse to create single-quantum (SQ) ¹³C magnetization.
• ¹³C acquisition. Broadband proton decoupling is applied during the whole of the sequence. A variant using composite pulses: It is also possible to refocuse X-X coupling:

In modified sequences, INEPT ( 82JMR180-46 ), DEPT ( 85JMR1-62 and 90JMR129-89 ), or heteronuclear CP ( 94JMRA113-109 ) pulse trains have been incorporated as a preparation period. Improved sensitivity can be achieved due to polarization transfer and, in addition, the repetition rate can also be increased because the experiment starts from ¹H magnetization

Some applications: 90MRC33