Restructure calibration compound

[NRayya]

• [x] We should have the hierarchy:

  • calibration compound
  • chemical shift calibration compound
    • chemical shift reference compound
  • concentration calibration compound

• [x] Enhance definitions:

  • calibration compound: A molecular entity that is used as a calibration compound in nuclear magnetic resonance (NMR) spectroscopy.
  • chemical shift calibration compound: A molecular entity that is used as a chemical shift calibration compound in nuclear magnetic resonance (NMR) spectroscopy.
  • chemical shift reference compound: A molecular entity that is used as a chemical shift reference compound in nuclear magnetic resonance (NMR) spectroscopy.
  • concentration calibration compound: A molecular entity that is used as a concentration calibration compound in nuclear magnetic resonance (NMR) spectroscopy.
  • calibration compound role: A compound that produces one or more peaks used to calibrate the NMR spectrometer and/or the spectrum.
  • chemical shift calibration compound role: A compound that produces one or more peaks used for chemical shift calibration.
  • chemical shift reference compound role: A compound that produces the peak used as reference frequency in the δ chemical shift scale.
  • concentration calibration compound role: A compound of a known concentration that produces one or more peaks used to calibrate a spectrum for quantification.

• [x] Remove its synonyms of reference compound: "reference compound, reference standard".

• [x] Keep the classification by nucleus under the chemical shift reference and import compounds from CHEBI there according to IUPAC recommendations https://www.degruyter.com/document/doi/10.1351/pac200173111795/html

• [x] Rename chemical shift standard to chemical shift reference.

• [x] Remove children of concentration compound.

• [x] calibration compound and its children should be defined similarly to 'NMR solvent' according to the roles they bear.

  • For chemical shift standard this can be done by reusing CHEBI:'NMR chemical shift reference compound'.

• [ ] Update the import from CHEBI after closing #22

  • This should remove old reference compounds provided in nmrCV

[NRayya]

• Every shift reference can be used as calibration compound.
• There are no solvents that are used as shift references but as calibration compound.
• Chemical shift reference in NMR is always 0, while calibration compound can have different ppm.

[NRayya]

Nuclei in nmrCV that didn't get a reference compound from IUPAC:

• [ ] 2H

[NRayya]

What I have done so far in calibration

1. Enhance calibration compound annotations. We still need a precise definition --> done in be66814135bbcab51324345244cf1f3be3127769 & f169762e83f3de4190966f5070bb26d0587e55bb
2. Enhance chemical shift standard annotations. We still need a precise definition and to clean old nmrCV entries --> done in d208f755718b50e9594709f44be837100e5b28a9
3. Add new classes for grouping the references by the nuclei according to IUPAC recommendations in addition to enhancing the annotations of existing ones --> done in 113a2a0e47a16fb1071dbaf69be2b1fd14804d0a
4. Obsolete old nmrCV references in favour of imported CHEBI equivalent --> done in 75f3de33fe50fadeb212eda412e9d4f475245bf9
5. Move imported CHEBI references under the corresponding grouping parents. We still need to refresh CHEBI:229458 import --> done in 04bc1d7c27a691b5955e97520ba6ff0c8e68cc78
6. Obsolete old nmrCV references that are not recommended by IUPAC. These entities are still imported from IUPAC by having the role NMR chemical shift reference compound. We need to figure their actual roles and clean them in CHEBI. --> done in e68e9749e4a827d0c3ea82b210c25fc9d8a92151