Gradient heteronuclear multiple spectrum

When we collect a 2-D NMR spectrum, both the second frequency dimension data (fj or Fj) and the first frequency dimension data (f2 or F2) may be phase sensitive. (Note that fj and f2 appear to be reversed but this naming convention derives from the order of their time domain precedents, tj and t2, in the NMR pulse sequence.) Zero-and first-order phasing of the second dimension of a 2-D NMR data set is required in many cases. Some experiments, most notably the gradient-selected heteronuclear multiple bond correlation (gHMBC) experiment, use the absolute value of the signal and hence do not require phasing. 

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