Coherence during data processing

To exploit the acquisition of both Jch and "Jch coherences, for each increment of the evolution time, t, two FIDs with phase 2 (> or -x, respectively) are acquired and stored in separate locations. In the first phase of data processing, each separately stored set of i data is processed separately. To disentangle the Jch and "Jch responses, the individually processed data are added and subtracted from each other to recover the individual spectra. Obviously, since broadband decoupling is not applied during the pulse sequence, the JcH spectrum will be fully coupled as was the data from the MBOB experiment (see Section 3.4.1). If X-decoupled direct correlation data are desired, the authors - note that a refocused variant of the experiment can be employed... 

The HMQC experiment gives exactly the same result as the HSQC, and the data is processed in the same way. There are some differences in sensitivity and peak shape that depend on the size and complexity of the molecule, and the pros and cons of the two experiments are the subject of some debate in the literature. Because it relies on double-quantum and zero-quantum coherences (DQC and ZQC) during the evolution (t ) period, the HMQC is more difficult to explain and understand than HSQC, which uses only the familiar singlequantum transitions that can be diagramed and analyzed using vectors. We discuss it here because it forms the basis of the HMBC (multiple-bond) experiment. 

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