Infrared (IR) and Raman spectra of 5-aminouracil were recorded in the region 200–4,000 cm − 1. Assuming under the Cs point group that the distribution of the normal mode of vibrations between the two species are planar (a′) and non-planar (a″), given by 25a′ + 11a″ of which 30 modes (21a′ + 9a″) correspond to the uracil moiety and six modes (4a′ + 2a″) correspond to the NH2 group, with a comparison of theoretically ab initio calculated frequencies, the results are in reasonably good agreement with the experimental IR and Raman spectra. Consistent assignments have been made for the internal modes of the NH2 group, especially for the anti-symmetric NH2 stretching and bending modes. The non-equivalence of the two NH bonds of the NH2 group suggests a difference in the strength of the two hydrogen bonds on the pyrimidine ring. Symmetry and anti-symmetry NH stretching modes of the NH2 group show the invalidity of the empirical relationship. These two NH2 stretching frequencies are distinctly separated from the CH/NH ring stretching frequencies. A strong and sharp IR band that acts at 3,380 cm − 1 could be identified as the anti-symmetric NH2 mode whereas the band at 3,290 cm − 1 smaller density could be identified as the symmetric NH2 stretching mode.

中文翻译：

---

5-氨基尿嘧啶的 FTIR 和拉曼光谱与从头计算频率模式的比较


5-氨基尿嘧啶的红外 (IR) 和拉曼光谱记录在 200–4,000 cm - 1 区域。假设在 Cs 点组下，两种物质之间的正则振动模式分布为平面 (a') 和非平面-平面（a”），由25a' + 11a”给出，其中30个模式（21a' + 9a”）对应于尿嘧啶部分，6个模式（4a' + 2a”）对应于NH2基团，比较理论上从头计算频率，结果与实验红外和拉曼光谱相当吻合。对NH2基团的内部模态进行了一致的分配，特别是对反对称NH2拉伸和弯曲模态。 NH2 基团的两个 NH 键不等价表明嘧啶环上两个氢键的强度不同。 NH2基团的对称性和反对称性NH伸缩模式表明经验关系的无效性。这两个 NH2 伸缩频率与 CH/NH 环伸缩频率明显分开。在 3,380 cm - 1 处作用的强而尖锐的红外谱带可以被识别为反对称 NH2 模式，而在 3,290 cm - 1 处较小密度的谱带可以被识别为对称 NH2 拉伸模式。