Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nam. 2, 166 10 Prague, Czech Republic.
J Org Chem. 2013 Oct 18;78(20):10121-33. doi: 10.1021/jo401441z. Epub 2013 Sep 27.
The formation of strong intramolecular hydrogen bonds was observed in a series of 2-amino-5-nitrosopyrimidines with alkylamino and arylamino substituents at positions 4 and 6. Mixtures of two rotamers differing in the orientation of the nitroso group were observed in the NMR spectra of the compounds where two distinct intramolecular hydrogen bonds could be formed. The ratio of the two rotamers depends strongly on the character of the substituents at positions 4 and 6 and can be finely tuned over a broad range of conformation ratios. The experimental results were supported by DFT calculations, which also made it possible to explain the apparent contradiction in the experimental dependence of the rotamer ratio on the Hammett constants for the arylamino substituents. The UV/vis spectra of the compounds also significantly depend on the nature of the substituents; however, the orientation of the nitroso group does not have any influence on the position of the absorption bands in the spectra.
在一系列 2-氨基-5-硝基亚嘧啶中，观察到具有烷基氨基和芳氨基取代基的强分子内氢键的形成，这些取代基位于 4 位和 6 位。在化合物的 NMR 谱中观察到两种扭转异构体的混合物，它们在可以形成两个不同的分子内氢键的位置处存在硝基的不同取向。两种旋转异构体的比例强烈取决于 4 位和 6 位取代基的性质，并且可以在广泛的构象比例范围内进行精细调节。实验结果得到了 DFT 计算的支持，这也使得可以解释实验中旋转异构体比例对芳氨基取代基的 Hammett 常数的依赖性的明显矛盾。化合物的 UV/vis 光谱也明显取决于取代基的性质；然而，硝基的取向对光谱中吸收带的位置没有任何影响。
