The absorption spectra of some substituted pyrazines and their salts / by Frank Tutin and Frederic W. Caton.

  • Tutin, Frank.
Date:
[1910?]
Catalogue details

Licence: In copyright

Credit: The absorption spectra of some substituted pyrazines and their salts / by Frank Tutin and Frederic W. Caton. Source: Wellcome Collection.

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    region, blit one band shown by the corresponding hydrobromide just extends into the visible part of the spectrum, thus explaining the pale yellow colour of the salt in question. The shift of the absorp¬ tion bands towards the red end of the spectrum caused by the substitution of liydrobromic for hydrochloric acid is not nearly so great as that caused by the conversion of the base into its hydro¬ chloride, thus indicating that the alteration in position of the bands in the latter case must be due chiefly to salt-formation, and only in a minor degree to the weight or nature of the acid radicle attached. The di- and tetra-methoxy-bases of the 2: 6-series, and all of the salts show two absorption bands, but in the case of 2 : 6-diphenyl- Fig. 4. Oscillation frequencies. 2000 2500 3000 3500 4000 o % 2000 x I 1800 i rO 5 1600 * fO 1 1400 2 1200 <**«* | 1000 © 800 - 2 : 5-Diphenylpyrazine. . 2 : 5-Diphenylpyrazine hydrochloride. pyrazine only one band is seen. Nevertheless, it is considered most probable that the absorption of all three 2 : 6-substituted bases is, in reality, similar, the second absorption band of the last-mentioned base being lost owTing to the absorption shown by the chloroform which was used as a solvent. The curves yielded by 2 : 5-diphenylpyrazine and its monohydro¬ chloride, and by ;pp'-dimethoxy-2 : 5-diphenylpyrazine and the corre¬ sponding salt of this base, are shown in Figs. 4 and 5 respectively. It will be observed in the case of these 2: 5-substituted bases that the curves show only one absorption band, whilst two such are exhibited by the curves obtained from the salts. One possible