Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt.
Spectrochim Acta A Mol Biomol Spectrosc. 2014 Jan 3;117:587-97. doi: 10.1016/j.saa.2013.09.057. Epub 2013 Sep 19.
The electronic absorption spectra of 6-ethyl-4-hydroxy-2,5-dioxo-pyrano[3,2-c] quinoline 1, 6-ethyl-4-hydroxy-3-nitro-2,5-dioxo-pyrano[3,2-c] quinoline 2, 6-ethyl-4-chloro-2,5-dioxo-pyrano[3,2-c] quinoline 3, 6-ethyl-3-nitro-4-chloro-2,5-dioxo-pyrano[3,2-c] quinoline 4, 6-ethyl-4,5-dioxopyrano[3,2-c] quinoline 5, and 6-ethyl-3-nitro-6H-pyrano [3,2-c]quinoline-4,5-dione 6, were measured in polar (methanol) as well as nonpolar (dioxane) solvents. The geometries were optimized using B3LYB/6-311G (p,d) method. The most stable geometry of the studied compounds, 1-6, is the planar structure as indicates by the values of the dihedral angles. The insertion of a nitro group in position 3 in both α- and γ-pyrone ring decreases the energy gap and hence increases the reactivity of 3 and 6 compounds. Assignment of the observed bands as localized, delocalized and/or of charge transfer (CT) has been facilitated by TD-DFT calculations. The correspondences between the calculated and experimental transition energies are satisfactory. The solvent and substituent effects have been investigated. Chloro-substituent has a higher band position and intensity effects on the spectra more than hydroxyl or nitro groups.
6-乙基-4-羟基-2,5-二氧代吡喃并[3,2-c]喹啉 1、6-乙基-4-羟基-3-硝基-2,5-二氧代吡喃并[3,2-c]喹啉 2、6-乙基-4-氯-2,5-二氧代吡喃并[3,2-c]喹啉 3、6-乙基-3-硝基-4-氯-2,5-二氧代吡喃并[3,2-c]喹啉 4、6-乙基-4,5-二氧代吡喃并[3,2-c]喹啉 5 和 6-乙基-3-硝基-6H-吡喃并[3,2-c]喹啉-4,5-二酮 6 的电子吸收光谱在极性（甲醇）和非极性（二氧六环）溶剂中进行了测量。采用 B3LYB/6-311G（p，d）方法对几何形状进行了优化。研究化合物 1-6 的最稳定几何形状是平面结构，这表明二面角的值。在α-和γ-吡喃酮环的 3 位插入硝基基团会降低能隙，从而增加 3 和 6 化合物的反应性。通过 TD-DFT 计算，有助于将观察到的带分配为局域化、离域化和/或电荷转移（CT）。计算和实验跃迁能量之间的对应关系令人满意。研究了溶剂和取代基的影响。氯取代基对光谱的带位置和强度影响比羟基或硝基基团更高。
