Double quantum transfer

INADEQUATE Incredible natural abundance double quantum transfer experiment, segregates AB or AX systems due to homonuclear one-bond couplings of less abundant nuclei, e.g. 

The NMR techniques discussed so far provide information about proton-proton interactions (e.g., COSY, NOESY, SECSY, 2D y-resolved), or they allow the correlation of protons with carbons or other hetero atoms (e.g., hetero COSY, COLOC, hetero /resolved). The resulting information is very useful for structure elucidation, but it does not reveal the carbon framework of the organic molecule directly. One interesting 2D NMR experiment, INADEQUATE (Incredible Natural Abundance Double Quantum Transfer Experiment), allows the entire carbon skeleton to be deduced directly via the measurement of C- C couplings. 

INADEQUATE stands for Incredible Natural Abundance DoublE QUAntum Transfer Experiment. Again, we refer you to NMR textbooks for an explanation of the principles. Here we only present the result, which is shown in Fig. 20 for the diester 2. 

There is also the rather famous experiment known as 2D INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment) which allows us to correlate carbon-13 with carbon-13. Potentially this experiment is very useful, since it allows us to see directly which carbon atoms are directly bonded. However, you will remember that the natural abundance of carbon-13 is only 1.1%, so a carbon-13/carbon-13 correlation requires us to detect only about 0.01% of the carbon nuclei present. Thus the experiment is very insensitive and requires large amounts of both sample and measuring... 

High on any NMR spectrocopist s wish list would be a technique that could be used to establish connectivities directly between carbon atoms. Such a technique does exist and it goes by the name of INADEQUATE (incredible natural abundance double quantum transfer experiment). Whilst this might sound fantastic in theory, everything in the garden is far from rosy. 

A study of the NMR spectra was carried out, and the shifts of the olefinic carbon atoms of 18 2 (9Z,1 E) (36) and (9/i, 11Z) (43) were readily identified by a combination of incredible natural abundance double quantum transfer experiment (INADEQUATE),... 

Incredible natural abundance double quantum transfer experiment... 

INADEQUATE involves effective suppression of the strong central signal. The process (d) -> (e) in Fig. 2.48, denoted as double quantum transfer, does not at all enhance the 13C—13C satellites. Their signafnoise ratio remains at 0.5% of the normal carbon-13 NMR sensitivity. 

The AB and AX systems of all 13C —13C bonds appear in one spectrum when the INADEQUATE pulse sequence (Fig. 2.48) is applied. Complete interpretation usually becomes difficult in practice due to signal overlapping, isotope shifts and AB effects (Section 2.9.4). A separation of the individual 13C— 13C two-spin systems by means of a second dimension would be desirable. It is the frequency of the double quantum transfer (d e) in Fig. 2.48 which introduces a second dimension to the INADEQUATE experiment. This double quantum frequency vDQ characterizes each 13CA — I3CX bond, as it depends on the sum of the individual carbon shieldings vA and vx in addition to the frequency v0 of the transmitter pulse located in the center of the spectrum if quadrature detection is applied [69c, 71] ... 

The incredible natural abundance double quantum transfer experiment (INADEQUATE) was proposed by Ray Freeman in 1980.1 2 The acronym of this remarkable technique sat high among the many NMR acronyms since, at the time of its birth, it accurately described all its attributes. INADEQUATE was seen as an incredible experiment with vast potential its widespread applications are dwarfed only by its inadequate sensitivity. Depending on the equipment available, an ovemight-to-weekend INADEQUATE experiment on a medium-sized molecule would typically require hundreds of milligrams of sample. Only recently have such unfavourable requirements been addressed with advent of cryogenically cooled probes. Now, INADEQUATE experiments using samples of 5-10 mg have become realistic propositions. 

Whereas the structural assignment by one-dimensional 13C NMR spectroscopy is unambiguous in the case of D2-Cj(,2,51 Achiba and co-workers were able to determine the carbon atom connectivity by 2D 13C NMR INADEQUATE (incredible natural abundance double-quantum transfer experiment) analysis performed on an isotopically enriched sample (20% 13C).58 In particular, they found that the observed chemical shifts correlate well with the curvature of the spheroid, the more strongly pyramidalized carbon atoms being shifted toward lower magnetic field. 

ID INADEQUATE (Incredible Natural Abundance Double Quantum Transfer Experiment)... 

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