Near Infrared Absorption Spectra of Uracil, 5-Chlorouracil, and Thymine

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Abstract
Absorption spectra of approx. 0.2 [image] solns. of these pyrimidines in fused SbCl3 at 100[degree]C in the range between 1.3 and 2.4u are descr. and compared with those of phenol and acetamide. All 3 pyrimidines show bands at 1.5 u corresponding with that of acetamide, and probably due to the first N-H overtone. Since phenol absorbs strongly at 1.43 u corresponding, to the first O-H overtone while the pyrimidines do not, it is concluded that the pyrimidines are in the keto form when dissolved in SbCl3. Characteristic absorption at 1.65 u is attributed to the first C-H overtone characteristic of ring compounds. The pyrimidines and acatamide but not phenol show absorption at 1.99-2.00 u, probably due to the second carbonyl overtone; all but acetamide absorb at 2.13 u, possibly due to a combination of the fundamental valence and deformation vibrations of a ring C-H group.