Infrared spectra pyridazines

However, in 2,3,5-trifluoro-6-hydroxypyrazine (47), the infrared spectrum of the solid was reported to show no absorption attributable to the carbonyl group, and its ultraviolet spectrum (in ethanol) was similar to that of 23,5-trifluoro-6-methoxypyrazine, thus indicating that it was a true hydroxy compound (851). A similar phenomenon has been observed in the pyridine (1087-1089) and pyrimidine (1090) series, but differs from observations in the pyridazine series (1091). 

Brown neutral polypyridazine can be prepared by electrochemical undoping of the oxidized polymer [198]. The undoped polymer has a band gap of about 1.8 eV. The infrared spectrum has features similar to that of the monomer, in addition to peaks that can be assigned to para-substituted pyridazine. Chemical analysis is consistent with the repeat formula, C4N2H2. 

Amino-pyrazines and -pyridazines have been shown to exist predominantly in the amino form by infrared spectroscopic studies (cf. Table VI). Ultraviolet spectral data have been interpreted to indicate that 4-aminocinnoline exists predominantly in the imino form 256, but this conclusion, which was based on comparison of its spectrum with those of cinnolin-4-one and 4-ethoxycinnoline, is probably incorrect. Ultraviolet spectroscopic data strongly support the predominance of amino structures for 2-aminopyrazine (257) and 2-aminoquin-oxaline how ever, the former compound was at first erroneously concluded to exist in the imino form from ultraviolet spectral evidence. Isolation of two isomers of 2-amino-8-dimethylamino-3-methylphenazine, assigned the amino and imino structures 258 and 259, respectively, has been claimed, but it is very unlikely that these assignments are correct. 

The association constant of pyridazine with ethanol was found to be 4.9 (from electronic absorption spectra) and 6.8 (infrared absorption spectra), and the corresponding values for the strength of the hydrogen bond are 4.2 and 4.6 kcal. The hydrogen-bonded form of P3n-idazine was considered to comprise one alcohol at one azine-nitrogen at small mole ratios of alcohol to azine and to involve the second nitrogen at high mole ratios (an additional shift in the electronic spectrum. The association constants (3.1-3.8) of pyridine, quinoline, and isoquinoline with methanol in carbon tetrachloride have been determined by infrared spectroscopy. 

Complete infrared and Raman data for pyridazine are given and assignments were made. A review by Katritzky and Ambler includes infrared data for pyridazine and other heteroaromatic compounds. Infrared spectroscopy has been applied also to the study of hydrogen-bonded complexes with phenol. Calculations on the vibrational spectrum of pyridazine have been performed. ... 

Assignments for pyridazine and pyrazine were suggested by Ito et al. [40], who noted that the latter differed from other heteroaromatics in having no infrarred absorptions above 1480 cm". However, this is a consequence of its symmetry and the usual four bands in the 1600—1400 cm" range are shown in the Raman spectrum. Several bands also appear in the infra-red when the symmetry is lost by substitution. Alkyl pyrazines show three or four bands in this range. Pyridazines have been studied as 3 6-substituted compounds and show two bands between 1600—1540 cm" and 1430— 1395 cm" [63]. Both series show medium to weak bands between 1300 and 1000 cm" from in plane CH bends and ring modes. These are better seen in the Raman spectra [44]. Below 1000 cm" the out of plane CH bends appear. Pyridazine has its as a band at 760 cm" which would correspond to four adjacent hydrogens, and pyrazine at 804 cm". ... 

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