HMQC and HSQC NMR data are commonly used to correlate the chemical shifts of protons and 13C (or 15N) across one chemical bond via the J coupling interaction. The data are 1H detected, with the 1H chemical shift in the horizontal F2 domain and the 13C (or 15N) chemical shift in the vertical F1 domain. In the case of 1H and 13C, the technique depends on protons bonded to 13C. 1H–12C spin pairs provide no coupling information and are suppressed by the method. If one is to observe the 1H signal of a 1H-13C spin pair, one expects to observe a doublet with splitting 1JH-C (i.e. the 13C satellites). Likewise, if one is to observe the 13C signal of a 1H-13C spin pair, one expects to observe a doublet with the same splitting. 2D HSQC spectra are normally presented with both 1H and 13C decoupling yielding a simplified 1H-13C chemical shift correlation map over one chemical bond. The figure below shows one of the most commonly used gradient HSQC pulse sequences. The 1H and 13C decoupling elements of the sequence are highlighted in yellow and pink, respectively.