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Next‐generation quantum theory of atoms in molecules for the ground and excited state of the ring‐opening of cyclohexadiene
摘要： The factors underlying the experimentally observed branching ratio (70:30) of the (1,3-cyclohexadiene) CHD ! HT (1,3,5-hexatriene) photochemical ring-opening reaction are investigated. The ring-opening reaction path is optimized by a high-level multi-reference DFT method and the density along the path is analyzed by the quantum theory of atoms in molecules (QTAIM) and stress tensor methods. The performed density analysis suggests that, in both S1 and S0 electronic states, there exists an attractive interaction between the ends of the fissile σ-bond of CHD that steers the ring-opening reaction predominantly in the direction of restoration of the ring. It is suggested that opening of the ring and formation of the reaction product (HT) can only be achieved when there is a sufficient persistent nuclear momentum in the direction of stretching of the fissile bond. As this orientation of the nuclear momentum vector can be expected relatively rare during the dynamics, this explains the observed low quantum yield of the ring-opening reaction.
关键词： QTAIM,ring-opening,cyclohexadiene,conical intersection,stress tensor
更新于2025-09-23 15:23:52
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Insight into the electron density distribution in an O,N-heterocyclic stannylene by means of high resolution x-ray diffraction analysis
摘要： In this paper we present the synthesis and results of a high-resolution single crystal X-ray diffraction experiment on the O,N-heterocyclic stannylene (t-BuAPSn) (1) containing the chelate 4,6-di-tert-butyl-N-tert-butyl-o-aminophenolate ligand. The experimental work is accompanied by a charge density study based on a topological analysis according to quantum theory of atoms in molecules (QTAIM) together with a NBO calculation of the crystal packing fragment containing a Sn-Sn bond. According to QTAIM, the Sn-Sn interaction is covalent (?2ρ(r)<0, he(r)<0). In the view of NBO analysis, there are two donor-acceptor bonding interactions between the tin atoms of adjacent molecules. The Sn-Sn bond energy evaluated by the Espinosa-Molins-Lecomte correlation is equal to ?9.1 kcal/mol. We carried out the investigation of source function not only in CP(3,-1) on the Sn-Sn bond but also on NCI-defined isosurface (λ2<0). The source function shows that the electron density from the Sn basins extensively contributes to the formation of this Sn–Sn bond in 1.
关键词： aminophenol,QTAIM theory,electron density distribution,stannylene,nature and energy of Sn-Sn interaction
更新于2025-09-23 15:19:57
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Synthesis, physicochemical and quantum chemical studies on a new organic NLO crystal: Cinnamoylproline
摘要： Cinnamoylproline was synthesized and the crystal was grown from solution by the slow evaporation method. The crystal belongs to the trigonal crystal system with non-centrosymmetric space group P31. The calculated geometry and experimental geometry from single crystal X-ray data were compared. Intermolecular interactions were studied using Hirshfeld surface analysis and its real space functions were calculated using Atoms In Molecules (AIM) and its isosurfaces were visualized using Non-covalent interaction analysis. Optical transparency of the crystal was analyzed by UV-Vis analysis and it was found that the crystal has good optical transparency in the visible range and the lower cut-off wavelength was found to be 326 nm. In the photoluminescence spectrum, a broad emission peak at 369 nm was observed. The functional groups were analyzed using FTIR techniques and the vibrational frequencies from experimental and theoretical values were compared. It was inferred from the TG-DTA studies that the crystal was thermally stable up to 375°C. Kurtz-Perry powder SHG analysis was also carried out with KDP as a reference. It showed that the crystal has 1.08 times greater efficiency than KDP. The first hyperpolarizability tensor of the molecule was calculated theoretically and theoretical second order susceptibility was obtained and compared with the experimental susceptibility.
关键词： Non Covalent Interaction (NCI),Crystal growth,Hirshfeld surface analysis,cinnamic acid,QTAIM,First hyperpolarizability
更新于2025-09-04 15:30:14