白藜芦醇顺反异构体及第一三重激发态结构的理论研究

在B3LYP/6-311++G(d,p)水平对白藜芦醇顺反异构体及第一三重激发态进行了结构优化、频率计算和自然键轨道(Natural Bond Orbital,NBO)分析.在MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p)水平比较了白藜芦醇顺反异构体的能量.反式白藜芦醇整个分子呈平面结构,顺式白藜芦醇两苯环之间存在约30o扭角.第一三重激发态中两苯环几乎处于互相垂直的关系,C7-H5与C8-H6键也是几乎互相垂直的关系.顺式和反式白藜芦醇C7-C8的σ键成键情况分别为sp1.53-sp1.53和sp1.59-sp1.60,C7与C8各自提供p轨道形成π键,即形成C7=C8双键.三重态中,C7-C8的成键情况为sp1.92-sp1.89,没有p-pπ键,C7、C8均还有一个2p轨道未参与杂化,NBO分析证实C7、C8的各自剩下的2p轨道均几乎独立形成了高能量的反键轨道,分别垂直于单羟基和双羟基苯环,C7-C8键长明显长于白藜芦醇顺反异构体.顺式白藜芦醇比反式白藜芦醇的自由能高约1.3-2.5 kcal/mol,反式构型是热力学稳定构型.含时密度泛函方法(Time-Dependent Density Functional Theory,TD-DFT)方法,B3LYP/6-311++G(d,p)水平计算得反式和顺式白藜芦醇最强紫外吸收峰分别在330 nm和319 nm.     

Synthesis and NMR spectra of the syn and anti isomers of substituted cyclobutanes—evidence for steric and spatial hyperconjugative interactions

The syn and anti isomers of cis,cis-tricyclo[5.3.0.0^2,6]dec-3-ene derivatives have been synthesized and their ¹H and ¹³C NMR spectra unequivocally analyzed. Both their structures and their ¹H and ¹³C NMR chemical shifts were calculated by DFT, the latter two calculations employing the GIAO perturbation method. Additionally, calculated NMR shielding values were partitioned into Lewis and non-Lewis contributions from the bonds and lone pairs involved in the molecules by accompanying NBO and NCS analyses. The differences between the syn and anti isomers were evaluated with respect to steric and spatial hyperconjugation interactions.     

Thermal Decomposition Kinetics of Ethane Halides and Derivatives（C_2H_（6-n）X_n（n = 1～3）;X = F,Cl,Br）：DFT Study and NBO Analysis

A theoretical study of the thermal decomposition kinetics of ethane halides(C2H6-nXn(n = 1～3);X = F,Cl,Br) has been carried out at the B3LYP/6-31++G** and B3PW91/631++G** levels of theory.Among these methods and comparison of activation parameters with available experimental values,the B3PW91/6-31++G** method is in good agreement with the experimental data.The analysis of bond order and natural bond orbital(NBO) charges,bond indexes,and synchronicity parameters suggest the elimination of HX in reactions 1～9(HF:compounds 1～3,HCl:compounds 4～6,and HBr:compounds 7～9) occur through a concerted and slightly asynchronous four-membered cyclic transition state type of mechanism.     

Reinvestigation of intramolecular hydrogen bond in malonaldehyde derivatives: An ab initio,AIM and NBO study

The RAHB systems in malonaldehyde and its derivatives at MP2/ 6‐311++G(d,p) level of theory were studied and their intramolecular hydrogen bond energies by using the related rotamers method was obtained. The topological properties of electron density distribution in O? H···O intramolecular hydrogen bond have been analyzed in term of quantum theory of atoms in molecules (QTAIM). Correlations between the H‐bond strength and topological parameters are probed. The results of QTAIM clearly showed that the linear correlation between the electron density distribution at HB critical point and RAHB ring critical point with the corresponding hydrogen bond energies was obtained. Moreover, it was found a linear correlation between the electronic potential energy density, V(r_cp), and hydrogen bond energy which can be used as a simple equation for evaluation of HB energy in complex RAHB systems. Finally, the similar linear treatment between the geometrical parameters, such as O···O or O? H distance, and Lp(O)→σ*_OH charge transfer energy with the intramolecular hydrogen bond energy is observed. © 2010 Wiley Periodicals, Inc., Int J Quantum Chem, 2011     

A novel single‐electron sodium bond system of H3C···Na?Y (YH,OH, F,CCH, CN,and NC)

A novel single‐electron sodium bond system of H₃C···Na? H (I), H₃C···Na? OH(II), H₃C···Na? F(III), H₃C···Na‐CCH(IV), H₃C···Na? CN (V) and H₃C···Na? NC (VI) complexes has been studied by using MP2/6‐311++G** and MP2/aug‐cc‐pVTZ methods for the first time. We demonstrated that the single‐electron sodium bond H₃C···Na? Y formed between H₃C and Na? Y (Y?H, OH, F, CCH, CN, and NC) could induce the Na? Y increased and stretching frequencies of I–IV and VI are red‐shifted, including the Na? N bond in complex V is blue‐shifted abnormally. The interaction energies are calculated at two levels of theory [MP2, CCSD(T)] with different basis. The results shows that the strength of binding bond in group 2 (IV–VI) with π electrons are stronger than that of group 1 (I–III) without π electrons. For all complexes, the main orbital interactions between moieties H₃C and Na? Y are LP₁(C)→LP*₁(Na). By comparisons with some related systems, it is concluded that the strength of single‐electron bond is increased in the order: hydrogen bond < bromine bond < sodium bond < lithium bond. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Influence of substitution on the strength and nature of CH···N hydrogen bond in XCCH···NH3 complexes

The effect of substitution on the strength and nature of CH···N hydrogen bond in XCCH···NH₃ (X = F, Cl, Br, OH, H, Me) and NCH···NH₃ complexes were investigated by quantum chemical calculations. Ab initio calculations were performed using MP2 method with a wide range of basis sets. With tacking into account the BSSE and ZPVE, the values of BEs decrease. Replacement of the nonparticipatory hydrogen atom of HCCH by the electronegative atoms (F, Cl, and Br), lead to the BEs increases. The BE corresponding to the replacement of the nonparticipatory hydrogen atom of HCCH by the OH and CH₃ groups decreases. A far greater enhancement of the interaction energy arises from replacement of HCCH by the more acidic HCN. The natural bond orbital analysis and the Bader's quantum theory of atoms in molecules were also used to elucidate the interaction characteristics of these complexes. The electrostatic nature of H‐bond interactions is predicted from QTAIM analysis. In addition, the relationship between the isotropic and anisotropic chemical shifts of the bridging hydrogen and binding energy of complexes as well as electron density at N···H BCPs were investigated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

N?H···S and S?H···N intramolecular hydrogen bond in β‐thioaminoacrolein: A quantum chemical study

The conformational study of β‐thioaminoacrolein was performed at various theoretical levels, HF, B3LYP, and MP2 with 6‐311++G(d,p) basis set, and the equilibrium conformations were determined. To have more reliable energies, the total energies of all conformers were recomputed at high‐level ab initio methods, G2MP2, G3, and CBS‐QB3. According to these calculations, the intramolecular hydrogen bond is accepted as the origin of conformational preference in thialamine (TAA) and thiolimine groups. The hydrogen bond strength in various resonance‐assisted hydrogen bond systems was evaluated by HB energy, geometrical parameters, topological parameters, and charge transfers corresponding to orbital interactions. Furthermore, our results reveal that the TAA tautomer has extra stability with respect to the other tautomers. The population analyses of the possible conformations by NBO predict that the origin of this preference is mainly due to the π‐electron delocalization in framework of TAA forms, especially usual π_C?C → π*_C?S and Lp (N) → π*_C?C charge transfers. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

FT-Raman, FT-IR spectra and total energy distribution of 3-pentyl-2,6-diphenylpiperidin-4-one: DFT method

FT-Raman and FT-IR spectra were recorded for 3-pentyl-2,6-diphenylpiperidin-4-one (PDPO) sample in solid state. The equilibrium geometries, harmonic vibrational frequencies, infrared and the Raman scattering intensities were computed using DFT/6-31G(d,p) level. Results obtained at this level of theory were used for a detailed interpretation of the infrared and Raman spectra, based on the total energy distribution (TED) of the normal modes. Molecular parameters such as bond lengths, bond angles and dihedral angles were calculated and compared with X-ray diffraction data. This comparison was good agreement. The intra-molecular charge transfer was calculated by means of natural bond orbital analysis (NBO). Hyperconjugative interaction energy was more during the π–π* transition. Energy gap of the molecule was found using HOMO and LUMO calculation, hence the less band gap, which seems to be more stable. Atomic charges of the carbon, nitrogen and oxygen were calculated using same level of calculation.     

Density functional theory calculations and vibrational spectral analysis of 3,5-(dinitrobenzoic acid)

The FT-IR and Raman spectra of 3,5-dinitrobenzoic acid (DNBA) have been recorded and analyzed. The equilibrium geometry, various bonding and harmonic vibrational wavenumbers have been calculated with the help of density functional theory (DFT) method. Most of the vibrational modes are observed in the expected range. Mulliken population analysis shows the interactions C-N-O?H-C and C-O?H-C. The most possible interaction is explained using natural bond orbital (NBO) analysis. The strengthening and polarization of the CO bond increases due to the degree of conjugation. HOMO-LUMO energy and the thermodynamic properties are also evaluated.     

Physicochemical studies of molecular hyperpolarizability of imidazole derivatives

A series of substituted imidazoles have been synthesized in very good yield under solvent free condition by grinding 1,2-diketone, arylaldehyde, arylamine and ammonium acetate in the presence of molecular iodine as the catalyst. The short reaction time, good yield and easy workup make this protocol practically and economically attractive and the imidazoles are characterized by NMR spectra, X-ray, mass and CHN analysis. The push-pull character of series of imidazoles have been analyzed by the quotient of the occupations of the bonding (π) and anti-bonding (π*) orbitals of the central linking -N=C-C=C- unit. Excellent correlation of the push-pull parameter with the corresponding bond lengths d(CN) and d(CC) strongly recommend both the occupation quotients (π*/π) and the corresponding bond lengths are reasonable sensors for quantifying the push-pull character and for the molecular hyperpolarizability ?(0) of these compounds. To support the experimental results, theoretical calculations (heat of formation, NLO, NBO and vibrational analysis) were also made. Within this context, reasonable conclusions concerning the steric hindrance in the chromospheres, push-pull character, hyperpolarizability of the imidazoles and their application as NLO materials will be drawn.