Experimental information must be provided to enable other researchers to reproduce the work accurately. Figures should include error bars where appropriate and results should be accompanied by analyses of experimental uncertainty.
The experimental details and the characterisation data should be provided preferably as electronic supplementary information (ESI) although on occasion it may be appropriate to include some or all of this within the body of the article. This will depend on the nature of the research being reported.
Characterisation of new compounds
It is the responsibility of authors to provide fully convincing evidence for the homogeneity, purity and identity of all compounds they claim as new. This evidence is required to establish that the properties and constants reported are those of the compound with the new structure claimed. Referees will assess, as a whole, the evidence presented in support of the claims made by the authors. The requirements for characterisation criteria are detailed below.
Inorganic and organometallic compounds
A new chemical substance (molecule or extended solid) should have a homogeneous composition and structure. New chemical syntheses must unequivocally establish the purity and identity of these materials. Where the compound is molecular, minimum standards have been established.
For manuscripts that report new compounds or materials, data must be provided to establish unequivocally the homogeneity, purity and identification of these substances. In general, this should include elemental analyses that agree to within ±0.4% of the calculated values. In cases where elemental analyses cannot be obtained (for example, for thermally unstable compounds), justification for the omission of this data should be provided.
Note that an X-ray crystal structure is not sufficient for the characterisation of a new material, since the crystal used in this analysis does not necessarily represent the bulk sample. In rare cases, it may be possible to substitute elemental analyses with high-resolution mass spectrometric molecular weights. This is appropriate, for example, with trivial derivatives of thoroughly characterised substances or routine synthetic intermediates.
In all cases, relevant spectroscopic data (NMR, IR, UV-vis, etc) should be provided in tabulated form and as reproduced spectra; reproduced spectra should be included in the electronic supplementary information (ESI).
Mass spectrometric and spectroscopic data do not constitute proof of purity, and in the absence of elemental analyses additional evidence of purity should be provided (melting points, PXRD data, etc).
Experimental data for new substances should also include synthetic yields, reported in terms of grams or moles, and as a percentage. Where the compound is an extended solid, it is important to establish unequivocally the chemical structure and bulk composition.
Single crystal diffraction does not determine the bulk structure. Referees will normally look to see evidence of bulk homogeneity.
A fully indexed powder diffraction pattern, which agrees with single crystal data, may be used as evidence of a bulk homogeneous structure and chemical analysis may be used to establish purity and homogeneous composition.
The synthesis of all new compounds must be described in detail. Synthetic procedures must include the specific reagents, products and solvents and must give the amounts (g, mmol, for products: %) for all of them, as well as clearly stating how the percentage yields are calculated.
It should be unambiguous whether yields pertain to a crude product (specify purity if possible) or a purified product. They must also include all the characterisation data for the prepared compound or material. For a series of related compounds, at least one representative procedure that outlines a specific example that is described in the text or in a table and which is representative for the other cases, must be provided.
If a known compound is prepared by a new or modified synthetic procedure, the types of physical and spectroscopic data that were found to match cited literature data should be identified, and purity documentation should be provided as indicated in the previous paragraph for new compounds.
For all compounds, even when the isolation of a pure compound is not being claimed, the degree of purity must still be estimated and, at least for diamagnetic compounds, NMR spectroscopic data included in the electronic supplementary information as described above.
Peaks appearing in the provided spectra that do not belong to a compound of interest should be designated and assigned as much as possible.
Nano-sized materials (such as quantum dots, nanoparticles, nanotubes, nanowires)
For nano-sized materials it is essential that the authors not only provide detailed characterisation on individual objects (see above) but also a comprehensive characterisation of the bulk composition.
Characterisation of the bulk of the sample require determination of the chemical composition and size distribution over large portions of the sample.
The syntheses of all new compounds must be described in detail.
Synthetic procedures must include the specific reagents, products and solvents and must give the amounts (g, mmol, for products: %) for all of them, as well as clearly stating how the percentage yields are calculated. It should be unambiguous whether yields pertain to a crude product (specify purity if possible) or a purified product. They must also include all the characterisation data for the prepared compound or material.
For a series of related compounds, at least one representative procedure, which outlines a specific example that is described in the text or in a table and which is representative for the other cases, must be provided.
Organic compounds
Authors are required to provide unequivocal support for the purity and assigned structure of all compounds using a combination of the following characterisation techniques: analytical, physical, spectroscopic.
Analytical
Elemental analysis (within ±0.4% of the calculated value) is required to confirm 95% sample purity and corroborate isomeric purity. Authors are required to provide copies of 1H,13C NMR spectra and/or GC/HPLC traces in the electronic supplementary information (ESI) especially if satisfactory elemental analysis results cannot be obtained. For libraries of compounds, HPLC traces should be submitted as proof of purity.
The determination of enantiomeric excess of nonracemic, chiral substances should be supported with either SFC/GC/HPLC traces with retention times for both enantiomers and separation conditions (that is, chiral support, solvent and flow rate) or for Mosher Ester/Chiral Shift Reagent analysis, copies of the spectra.
Physical
Important physical properties - for example, boiling or melting point, specific rotation, refractive index, etc - including conditions and a comparison to the literature for known compounds should be provided. For crystalline compounds, the method used for recrystallisation should also be documented (that is, solvent, etc).
Spectroscopic
Mass spectra and a complete numerical listing of 1H,13C NMR peaks in support of the assigned structure, including relevant 2D NMR spectra and related experiments (that is, NOE, etc) is required. Authors are required to provide copies of these spectra. Infrared spectra that support functional group modifications, including other diagnostic assignments should be included.
High-resolution mass spectra are acceptable as proof of the molecular weight provided the purity of the sample has been accurately determined as outlined above.
The syntheses of all new compounds must be described in detail. Synthetic procedures must include the specific reagents, products and solvents and must give the amounts (g, mmol, for products: %) for all of them, as well as clearly stating how the percentage yields are calculated. It should be unambiguous whether yields pertain to a crude product (specify purity if possible) or a purified product. They must include the 1H,13C NMR spectra and MS data of this specific compound.
For multistep synthesis papers: spectra of key compounds and of the final product should be included. For a series of related compounds, at least one representative procedure, which outlines a specific example that is described in the text or in a table and which is representative for the other cases, must be provided.
Polymers
For all soluble polymers an estimation of molecular weight must be provided by a suitable method - for example, size exclusion chromatography, including details of columns, eluents and calibration standards, intrinsic viscosity, MALDI TOF, etc in addition to full NMR characterisation (1H,13C) as for organic compound characterisation (see above).
The synthesis of all new compounds must be described in detail. Synthetic procedures must include the specific reagents, products and solvents and must give the amounts (g, mmol, for products: %) for all of them, as well as clearly stating how the percentage yields are calculated. It should be unambiguous whether yields pertain to a crude product (specify purity if possible) or a purified product. They must also include all the characterisation data for the prepared compound or material.
For a series of related compounds, at least one representative procedure, which outlines a specific example that is described in the text or in a table and which is representative for the other cases, must be provided.
Biomolecules (for example, enzymes, proteins, DNA/RNA, oligosaccharides, oligonucleotides)
Authors should provide rigorous evidence for the identity and purity of the biomolecules described.
The techniques that may be employed to substantiate identity include mass spectrometry, LC-MS, sequencing data (for proteins and oligonucleotides), high field 1H,13C NMR, X-ray crystallography.
Purity must be established by one or more of the following.
- HPLC
- Gel electrophoresis
- Capillary electrophoresis
- High field 1H,13C NMR.
Sequence verification also needs to be carried out for nucleic acid cases involving molecular biology. For organic synthesis involving DNA, RNA oligonucleotides, their derivatives or mimics, purity must be established using HPLC and mass spectrometry as a minimum.
For new derivatives comprising modified monomers, the usual organic chemistry analytical requirements for the novel monomer must be provided (see Organic compounds). It is not necessary to provide this level of characterisation for the oligonucleotide into which the novel monomer is incorporated.
Computational results
Authors should supply enough data in the electronic supplementary information (ESI) for others to be able to reproduce the results and/or to make the results usable without repeating the calculations.
A description of specific programs and versions is required. If the author’s own or a modified version of a commercially available program is used, it is required that the program/code/modification be made available to the scientific community (QCPE, publication in a computational journal, commercially, etc).
A clear exposition of any nonstandard equations and algorithms used and, where feasible, tests of the codes in various limiting cases should also be provided. Final optimised coordinates and keywords should be provided.
For DFT computations, the choice of functional must be justified or the validation of the functional provided. The choice of basis sets must be explicitly discussed, including any deviation from standard basis sets.
Convergence criteria, integration parameters, active space definition in multireference calculations, and for open-shell systems, how spin states are handled, should be mentioned explicitly.
The exact definition of any applied numerical or symmetry constraint should be indicated. When relevant to the results of the study, data such as absolute energies, gross orbital populations, atomic spin densities, etc, should be supplied.
Where feasible, critical checkpoint/restart files should be saved and made available upon request. Input files are recommended to be included in the ESI.
General
It is the responsibility of the author(s) to provide the reviewers with the necessary information to evaluate the merit of the manuscript in terms of its scientific content. Failure to provide the necessary experimental evidence and data may result in the manuscript being withdrawn by the editor.
