Abstract The present work reports an experimental and theoretical study of molecular structure of 4-Amino-2-chloropyrimidine-5-carbonitrile (ACPC) in solid phase. Raman and infrared (IR) spectra of ACPC have been recorded in the region of 3600–100 cm −1 and 4000–200 cm −1 , respectively. Calculations with the methods of B3LYP and Moller–Plesset second perturbation (MP2) were carried out for structural and vibrational predictions. The computational approaches were tested and adapted by comparing the predicted spectra to results obtained experimentally. In order to assign the calculated frequencies for the recorded ones, a normal coordinate analysis has been performed for vibrations with respect to the nuclei displacements for all the fundamental frequencies. By computing and analyzing, in detail, the infrared and Raman spectra of ACPC, the changes in the vibrational features were probed by identifying two tautomers of ACPC; (i) amino ACPC which could exist in two conformational structures, and (ii) imino ACPC which could exist in four conformational structures. Both computational and spectral results were in favor of the amino tautomer with no evidence for the existence of interconversion between amino and imino forms. Moreover, only one of the amino ACPC conformers was found to be the most stable one where the hybridization of amino group was found to be sp 3 . The theoretical predictions agree well with the available experimental data, accounting for the interconversion process in the amino / imino functional groups. We demonstrate that vibrational spectroscopy constitutes a powerful tool for studying molecular structure due to its high sensitivity to changes in molecular geometry.

中文翻译：

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4-Amino-2-chloropyrimidine-5-carbonitrile 的拉曼光谱和红外光谱、法向坐标分析和从头计算

摘要 本工作报告了固相4-氨基-2-氯嘧啶-5-甲腈(ACPC) 分子结构的实验和理论研究。ACPC 的拉曼光谱和红外 (IR) 光谱分别记录在 3600-100 cm -1 和 4000-200 cm -1 区域。使用 B3LYP 和 Moller-Plesset 二次扰动 (MP2) 方法进行计算以进行结构和振动预测。通过将预测光谱与实验获得的结果进行比较，对计算方法进行了测试和调整。为了为记录的频率分配计算的频率，已经对所有基本频率的核位移的振动进行了法向坐标分析。通过对ACPC的红外光谱和拉曼光谱进行详细的计算和分析，通过鉴定ACPC的两个互变异构体来探测振动特征的变化；(i) 可以存在于两种构象结构中的氨基 ACPC，以及 (ii) 可以存在于四种构象结构中的亚氨基 ACPC。计算和光谱结果都支持氨基互变异构体，没有证据表明氨基和亚氨基形式之间存在互变。此外，只有一种氨基 ACPC 构象异构体被发现是最稳定的，其中氨基的杂交被发现是 sp 3 。理论预测与可用的实验数据非常吻合，说明了氨基/亚氨基官能团中的相互转化过程。