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3.0 Presentation of experimental data

3.1 Physical characteristics of compounds

Data associated with particular compounds should be listed after the name of the compound concerned, following the description of its preparation. The following is suggested as the order in which the most commonly encountered data for a new compound should be cited: yield, melting point, optical rotation, refractive index, elemental analysis, UV absorptions, IR absorptions, NMR spectrum, mass spectrum. Appropriate formats for the citation of each are as follows.

3.1.1 Yield. In parentheses after the compound name (or its equivalent). Weight and percentage are separated by a comma, e.g. the lactone (7.1 g, 56%).

3.1.2 Melting point. In the form mp 75 °C (from EtOH), i.e. the crystallization solvent in parentheses. If an identical mixed melting point is to be recorded, the form mp and mixed mp 75 °C is appropriate.

3.1.3 Optical rotation. The units should be stated in the preamble to the Experimental section, e.g. []_D values are given in 10^-1 deg cm² g^-1. Shown in the form []_D²² -22.5 (c 0.95 in EtOH), i.e. concentration and solvent in parentheses.

3.1.4 Refractive index. Given in the form n_D²² 1.653.

3.1.5 Elemental analysis. In the presentation of elemental analyses, both forms (Found: C, 63.1; H, 5.4. C₁₃H₁₃NO₄ requires C, 63.2; H, 5.3%) and (Found: C, 62.95; H, 5.4. Calc. for C₁₃H₁₃NO₄: C, 63.2; H, 5.3%) are acceptable. Analyses are normally quoted to the nearest 0.1%, but a 5 in the second place of decimals is retained. For identification purposes for new compounds, an accuracy to within ±0.3% is expected, and in exceptional cases, to within ±0.5% is required. If a molecular weight is to be included, the appropriate form is: [Found: C, 63.1; H, 5.4%; M (mass spectrum), 352 (or simply M⁺, 352). C₁₃H₁₃NO₄ requires C, 63.2; H, 5.3%; M, 352].

3.1.6 UV absorptions. These are given in the form _max(EtOH)/nm 228 (/dm³ mol^-1 cm^-1 40 900), 262 (19 200) and 302 (11 500). Inflections and shoulders are specified as 228infl or 262sh. Alternatively the following form may be used: _max (EtOH)/nm 228, 262 and 302 (/dm³ mol^-1 cm^-1 40 900, 19 200 and 11 500). log  may be quoted instead of .

3.1.7 IR absorptions. As follows: _max/cm^-1 3460 and 3330 (NH), 2200 (conj. CN), 1650 (CO) and 1620 (CN). The type of signal (s, w, vs, br) can be indicated by appended letters (e.g. 1760vs).

3.1.8 NMR data. For all spectra  values should be used, with the nucleus indicated by subscript if necessary (e.g. _H, _C). A statement specifying the units of the coupling constants should be given in the preamble to the Experimental section, e.g. J values are given in Hz. Instrument frequency, solvent, and standard should be specified. For example: _H(100 MHz; CDCl₃; Me₄Si) 2.3 (3 H, s, Me), 2.5 (3 H, s, COMe), 3.16 (3 H, s, NMe) and 7.3-7.6 (5 H, m, Ph). A broad signal may be denoted by br, e.g. 2.43 (1 H, br s, NH). Order of citation in parentheses: (i) number of equivalent nuclei (by integration), (ii) multiplicity (s, d, t, q), (iii) coupling constant, e.g. J_1,2 2, J_AB 4, (iv) assignment; italicisation can be used to specify the nuclei concerned (e.g. CH₃CH₂). The proton attached to C-6 may be designated C(6)H or 6-H; the methyl attached to C-6, 6-Me or C(6)Me. Mutually coupled protons in ¹H NMR spectra must be quoted with precisely matching J values, in order to assist thorough interpretation. In instances of any ambiguities when taking readings from computer print-outs, mean J values should be quoted, rounded to the nearest decimal point.

3.1.9 Mass spectrometry data. Given in the form: m/z 183 (M⁺, 41%), 168 (38), 154 (9), 138 (31) etc. The molecular ion may be specified as shown if desired. Relative intensities in parentheses (% only included once). Other assignments may be included in the form m/z 152 (33, M - CH₃CONH₂). Metastable peaks may be listed as: M* 160 (189174), 147 (176161), etc. The type of spectrum (field desorption, electron impact, etc.) should be indicated. Exact masses quoted for identification purposes should be accurate to within 5 ppm (EI and CI) or 10 ppm (FAB or LSIMS).

3.1.10 Literature citations. If comparison is to be made with literature values, these should be quoted in parentheses, e.g. mp 157 °C (from chloroform) (lit.,¹⁹ 156 °C), or _max/cm^-1 2020 and 1592 (lit.,²⁴ 2015 and 1600).

3.1.11 Experiments involving microorganisms. For work involving microorganisms, sufficient detail should be provided to identify the species being used.

3.1.12 A typical experimental section. The paragraph below exemplifies many of the points made in the preceding sections.

3.2 Characterisation of new compounds

It is the responsibility of authors to provide fully convincing evidence for the homogeneity and identity of all compounds they claim as new. Evidence of both purity and identity is required to establish that the properties and constants reported are those of the compound with the new structure claimed.

A compound is considered as new (a) if it has not been prepared before, (b) if it has been prepared before but not adequately purified, (c) if it has been purified but not adequately characterized, (d) if, earlier, it has been assigned an erroneous constitution, or (e) if it is a natural product isolated or synthesized for the first time. In preliminary communications compounds are often recorded with limited characterizing data; in spite of (c) above later preparations of such compounds are not considered as new if the properties previously reported are confirmed; the same applies to patents.

Referees will assess, as a whole, the evidence in support of the homogeneity and structure of all new compounds. No hard and fast rules can be laid down to cover all types of compound, but evidence for the unequivocal identification of new compounds should wherever possible include good elemental analytical data; an accurate mass measurement of a molecular ion does not provide evidence of purity of a compound and must be accompanied by independent evidence of homogeneity e.g. HPLC. Low-resolution mass spectrometry must be treated with even more reserve in the absence of firm evidence to distinguish between alternative molecular formulae. Where elemental analytical data cannot be obtained, appropriate evidence which is convincing to an expert in the field may be acceptable, but authors should include, for the referees, an explanation of the special nature of their problem.

Spectroscopic information necessary to the assignment of structure should be given. Just how complete this information should be must depend upon the circumstances; the structure of a compound obtained from an unusual reaction or isolated from a natural source needs much stronger supporting evidence than one derived by a standard reaction from a precursor of undisputed structure. Authors are reminded that full spectroscopic assignments may always be treated as Supplementary Data (see Section 3.5) where their importance does not justify their inclusion in the published paper.

Particular care should be taken in supporting the assignments of stereochemistry (both relative and absolute) of chiral compounds reported, for example by NMR spectroscopy, X-ray crystallography, polarimetry or correlation with known compounds of undisputed configuration. In cases where mixtures of isomers are generated (e.g. E/Z isomers, enantiomers, diastereoisomers), the constitution of the mixture should usually be established using appropriate analytical techniques (e.g. NMR spectroscopy, GLC, HPLC) and reported in an unambiguous fashion. In the case of asymmetric reactions in which enantiomeric mixtures are prepared, the direct measurement of the enantiomer ratio and its reporting expressed as an enantiomeric excess (ee) is recommended, and is preferred to (less reliable) polarimetry methods.

3.3 Characterisation within chemical biology

Where compounds are synthesised for testing in biological systems, sufficient evidence for purity and identity must be provided such that the results of the experiment may be trusted.

The homogeneity of oligomeric compounds (peptides, saccharides, nucleotides etc.) should be determined by HPLC analyses or by other appropriate analytical methods (e.g. capillary electrophoresis) with a purity of not less than 95%.