Department of Physics, Banaras Hindu University, Varanasi, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2010 Jan;75(1):267-76. doi: 10.1016/j.saa.2009.10.022. Epub 2009 Oct 21.
DFT calculations at the B3LYP/6-311++G** level have been carried out to study the vibrational characteristics of the neutral molecules, anionic and cationic radicals of uracil, 2-thiouracil and 4-thiouracil. In the U molecule, C=C bond loses its double bond character and magnitude of the C=C stretching frequency decreases significantly as a result of radicalization. Frequency for the in-plane deformation mode of C=O increases when a sulfur atom is substituted for the oxygen atom at the site C(2) in the uracil molecule but decreases when a sulfur atom is substituted for the oxygen atom at the site C(4). The magnitude of both the N-H stretching frequencies decreases in all the radical cations as compared to their neutral molecules. Radicalization leads to significant changes in the magnitudes and intensities corresponding to some of the normal modes for all the three cases. Removal of an electron leads to decrease in the electronic charge mainly from the sulfur atom in the case of 2-TU and 4-TU, whereas it is distributed over the sites N(1), C(5), O(8) and O(10) in case of the U molecule.
在 B3LYP/6-311++G** 水平上进行了 DFT 计算，以研究尿嘧啶、2-硫代尿嘧啶和 4-硫代尿嘧啶的中性分子、阴离子和阳离子自由基的振动特性。在 U 分子中，C=C 键失去双键特征，C=C 伸缩频率显著降低，因为发生了自由基化。当在尿嘧啶分子中 C(2)位的氧原子被硫原子取代时，C=O 的面内变形模式的频率增加，但当 C(4)位的氧原子被硫原子取代时，频率降低。与中性分子相比，所有自由基阳离子的 N-H 伸缩频率都减小。自由基化导致所有三种情况下一些正则模式的幅度和强度发生显著变化。对于 2-TU 和 4-TU，去除一个电子会导致电子电荷主要从硫原子中减少，而对于 U 分子，电子电荷分布在 N(1)、C(5)、O(8)和 O(10)位置上。
