Our long-term investigations have been devoted the characterization of intramolecular hydrogen bonds in cyclic compounds. Our previous work covers naphthazarin, the parent compound of two systems discussed in the current work: 2,3-dimethylnaphthazarin (1) and 2,3-dimethoxy-6-methylnaphthazarin (2). Intramolecular hydrogen bonds and substituent effects in these compounds were analyzed on the basis of Density Functional Theory (DFT), Møller–Plesset second-order perturbation theory (MP2), Coupled Clusters with Singles and Doubles (CCSD) and Car-Parrinello Molecular Dynamics (CPMD). The simulations were carried out in the gas and crystalline phases. The nuclear quantum effects were incorporated a posteriori using the snapshots taken from ab initio trajectories. Further, they were used to solve a vibrational Schrödinger equation. The proton reaction path was studied using B3LYP, $\omega$B97XD and PBE functionals with a 6-311++G(2d,2p) basis set. Two energy minima (deep and shallow) were found, indicating that the proton transfer phenomena could occur in the electronic ground state. Next, the electronic structure and topology were examined in the molecular and proton transferred (PT) forms. The Atoms In Molecules (AIM) theory was employed for this purpose. It was found that the hydrogen bond is stronger in the proton transferred (PT) forms. In order to estimate the dimers’ stabilization and forces responsible for it, the Symmetry-Adapted Perturbation Theory (SAPT) was applied. The energy decomposition revealed that dispersion is the primary factor stabilizing the dimeric forms and crystal structure of both compounds. The CPMD results showed that the proton transfer phenomena occurred in both studied compounds, as well as in both phases. In the case of compound 2, the proton transfer events are more frequent in the solid state, indicating an influence of the environmental effects on the bridged proton dynamics. Finally, the vibrational signatures were computed for both compounds using the CPMD trajectories. The Fourier transformation of the autocorrelation function of atomic velocity was applied to obtain the power spectra. The IR spectra show very broad absorption regions between 700 cm${}^{-1}$–1700 cm${}^{-1}$ and 2300 cm${}^{-1}$–3400 cm${}^{-1}$ in the gas phase and 600 cm${}^{-1}$–1800 cm${}^{-1}$ and 2200 cm${}^{-1}$–3400 cm${}^{-1}$ in the solid state for compound 1. The absorption regions for compound 2 were found as follows: 700 cm${}^{-1}$–1700 cm${}^{-1}$ and 2300 cm${}^{-1}$–3300 cm${}^{-1}$ for the gas phase and one broad absorption region in the solid state between 700 cm${}^{-1}$ and 3100 cm${}^{-1}$. The obtained spectroscopic features confirmed a strong mobility of the bridged protons. The inclusion of nuclear quantum effects showed a stronger delocalization of the bridged protons.

中文翻译：

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从分子内作用力和分子间作用力的角度看萘甲素衍生物

我们的长期研究一直致力于表征环状化合物中的分子内氢键。我们之前的工作涵盖了萘甲素，这是当前工作中讨论的两个系统的母体化合物：2,3-二甲基萘甲素 ( 1 ) 和 2,3-二甲氧基-6-甲基萘甲素 ( 2)）。基于密度泛函理论 (DFT)、Møller-Plesset 二阶微扰理论 (MP2)、单双峰耦合簇 (CCSD) 和 Car-Parrinello 分子动力学分析了这些化合物中的分子内氢键和取代基效应。 CPMD）。模拟是在气相和结晶相中进行的。核量子效应是使用从 ab initio 轨迹拍摄的快照后验合并的。此外，它们还用于求解振动薛定谔方程。使用 B3LYP 研究质子反应路径，$\omega$B97XD 和 PBE 泛函与 6-311++G(2d,2p) 基组。发现了两个能量最小值（深和浅），表明质子转移现象可能发生在电子基态。接下来，以分子和质子转移 (PT) 形式检查电子结构和拓扑。分子中的原子 (AIM) 理论被用于此目的。发现氢键在质子转移 (PT) 形式中更强。为了估计二聚体的稳定性和对其负责的力，应用了对称适应扰动理论 (SAPT)。能量分解表明分散是稳定两种化合物的二聚体形式和晶体结构的主要因素。CPMD 结果表明，质子转移现象发生在两种研究化合物中，以及在两个阶段。在复合的情况下如图2所示，固态中的质子转移事件更频繁，表明环境效应对桥接质子动力学的影响。最后，使用 CPMD 轨迹计算两种化合物的振动特征。应用原子速度的自相关函数的傅立叶变换来获得功率谱。红外光谱显示在 700 cm${}^{-1}$–1700 厘米${}^{-1}$ 和 2300 厘米${}^{-1}$–3400 厘米${}^{-1}$ 在气相和 600 cm${}^{-1}$–1800 厘米${}^{-1}$ 和 2200 厘米${}^{-1}$–3400 厘米${}^{-1}$化合物1为固态。发现化合物2的吸收区域如下：700 cm${}^{-1}$–1700 厘米${}^{-1}$ 和 2300 厘米${}^{-1}$–3300 厘米${}^{-1}$ 对于气相和固态的一个宽吸收区，在 700 cm${}^{-1}$ 和 3100 厘米${}^{-1}$. 获得的光谱特征证实了桥连质子的强迁移率。包含核量子效应表明桥接质子的离域更强。