IR spectra of 18 kinds of substituted fluoropyrimidines and 20 kinds of substituted chloropyrimidines were measured, and discussion was made on the C-F stretching vibration, skeletal and ring vibration of fluoropyrimidine derivatives, and the C-Cl stretching vibration of chloropyrimidine derivatives. Sharp absorption bands appeared at 1029 and 1034 cm
-1 in the spectra of 2-fluoropyrimidines (I, II), in the 1047-1015 cm
-1 region of 4-fluoro- and 6-fluoropyrimidine derivatives (III-XI), at 1030 and 1042 cm
-1 of 2, 4-difluoropyrimidines (XII, XIII), at 1045 cm
-1 of 2-amino- and 2-amino-5-methyl-4, 6-difluoropyrimidine (XIV, XV), and at 1029 and 1026 cm
-1 of 2-phenyl- and 5-phenyl-4, 6-difluoropyrimidine (XVI, XVII), and these were assigned to the C-F stretching vibrations. A weak band was observed in the region of 713-694 cm
-1 in the spectra of all the fluoropyrimidine derivatives examined, which was presumed to be attributable to the ring vibrations, and it was possible to distinguish fluoropyrimidine derivatives from chloropyrimidine derivatives by the presence of this band. The skeletal vibrations of fluoropyrimidine derivatives were found in the region of 1626-1418 cm
-1, viz., in higher frequency region than those of the corresponding chloropyrimidine derivatives. Absorption bands in the region of 786-743 cm
-1 in chloropyrimidine derivatives were assigend to the C-Cl stertching vibrations.
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