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[[dipsi2etgpjcsix1, Sensitivity and Gradient- enhanced HETLOC|Bruker setup instructions]]

===What it does===
This 2D experiment measures remote CH J couplings at the natural abundance of <sup>13</sup>C isotope (mainly couplings between H and C atoms separated by two and three chemical bonds). Couplings are measured from the splitting of cross-peaks in the directly-detected F2 dimension (details described below).

Both F1 and F2 dimensions resolve <sup>1</sup>H chemical shifts. Dimension F1 (indirect) shows chemical shift of protons attached to <sup>13</sup>C atoms. Dimension F2 (direct) - chemical shift of "remote" <sup>12</sup>C-attached protons.

Cross peaks are <sup>1</sup>H-<sup>1</sup>H [[TOCSY]] signals. They are split in F1 dimension by <sup>1</sup>J<sub>CH</sub> coupling and in F2 dimension - by <sup>2,3</sup>J<sub>CH</sub> coupling.

Optionally, splitting in F1 can be scaled in the case when cross peaks overlap. In addition, in case of severe peak overlap, that splitting can be completely removed and sought couplings can be determined from two experiments: one with <sup>13</sup>C decoupling during [[FID]] acquisition and one - without.

===Reading data===
'''Reading <sup>2,3</sup>J<sub>CH</sub> couplings''': for a given [[TOCSY]] cross-peak at &delta;F1 corresponding to atom H<sub>a</sub> (attached to atom <sup>13</sup>C<sub>a</sub>) and &delta;F2 corresponding to atom H<sub>b</sub> (attached to NMR silent <sup>13</sup>C<sub>b</sub>), the coupling C<sub>a</sub>-H<sub>b</sub> will be equal the splitting of the peak in the directly detected F2 dimension.

===Overview===
A combined sequence made up by [[zz Filter|zz]] and [[X filter|X]] filter elements is used in the beginning of the pulse sequence ([[HETLOC]] experiment uses [[BIRD]] pulse for the same purpose). That sequence "selectively excites" <sup>13</sup>C-attached protons in the preparation phase.

The [[G-BIRD]] pulse in the middle of T<sub>1</sub> evolution does two things: (1) removes proton-proton coupling in F1 dimension, providing narrower, more intense lines compared to [[HETLOC]], also (2) this pulse insures that within T<sub>1</sub> period only <sup>13</sup>C-attached proton chemical shifts evolve. Magnetization of <sup>12</sup>C-attached is dephased by the combination of [[G-BIRD]] and the flanking opposing-strength pulsed field gradients.

An optional scaling of <sup>1</sup>J<sub>CH</sub> coupling is introduced to allow resolution of overlapping [[E.COSY]] multiplets.

Magnetization between the coupled nuclei is transferred via a sensitivity-enhanced [[TOCSY]] method.

Coupling values smaller then width of lines can be resolved in a single experiment because of splitting in F1 dimension.

<bibtex>
@article{uhri´n1998sag,
  title={Sensitivity-and Gradient-Enhanced Hetero ($\omega$1) Half-Filtered TOCSY Experiment for Measuring Long-Range Heteronuclear Coupling Constants},
  author={Uhr{\i}´n, D. and Batta, G. and Hruby, V.J. and Barlow, P.N. and K{\"o}v{\'e}r, K.E.},
  journal={Journal of Magnetic Resonance},
  volume={130},
  number={2},
  pages={155--161},
  year={1998},
  publisher={Elsevier},
  url={http://dx.doi.org/doi:10.1006/jmre.1997.1308}
}
</bibtex>

[[Category:Scalar Coupling]] [[Category:Small Molecule NMR]]

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