Palladium-triethylborane-triggered direct and regioselective conversion of allylic alcohols to allyl phenyl sulfones

A combination of Pd(OAc)2 (5 mol %), PPh3 (10 mol %), and Et3B (200 mol %) promotes the formation of allyl phenyl sulfones from the allylic alcohols directly with excellent yields under mild conditions. The activation of an alcohol group is not necessary which is achieved in situ. The conjugated dienols also were equally effective for the said transformation.     

Density functional theory studies on ice nanotubes

The structure and stability of quasi one-dimensional (1D) ice nanotubes (INTs) have been investigated using Density Functional Theory (DFT) based Becke's three parameter Lee-Yang-Parr exchange and correlation functional (B3LYP) method employing various basis sets. Four different INTs, namely, (4,0)-INT, (5,0)-INT, (6,0)-INT, and (8,0)-INT with different lengths have been considered in this study. The calculated stabilization energies (SEs) illustrate that the stability of INT is proportional to its length and diameter. Further, the encapsulation of various gas molecules (CO(2), N(2)O, CO, N(2), and H(2)) inside the INTs has also been investigated. The calculated SEs of different endohedral complexes reveal that all these gas molecules are stable inside the tubes. The Bader's theory of atoms in molecule (AIM) has been used to characterize intra- and inter-ring H-bonding interactions. The electron density topological parameters derived from AIM theory brings out the difference between the intra- and inter-ring H-bonds of INTs.     

Density functional theory studies on copper phenanthroline complexes

Density functional theory calculations have been employed to investigate the role of structural properties of copper phenanthroline complexes for DNA-cleavage activity. Structural changes imposed on the coordination geometries of Cu(phen)(2)(+,2+) (phen = 1,10-phenanthroline) linked by a serinol bridge (abbreviated as Clip) were studied, as well as their energetic profiles. Our calculations show that structures of these copper complexes (in this work named as clipped complexes) strongly depend on the position of the link, rather than on the copper oxidation state. Ionization energies slightly differ among the three selected complexes, while inner-sphere reorganization energies more markedly depend on the serinol link. However, the relative rates of the redox reaction of Cu(phen)(2), Cu(2-Clip-phen), and Cu(3-Clip-phen) were found not to correlate with their relative DNA-cleavage activity experimentally observed. Thus, the serinol link mainly affects the structural properties of copper phenanthroline complexes rather than their electronic properties. Docking simulations of clipped and nonclipped Cu(I) phenanthroline complexes on a DNA 16mer, d[CGCTCAACTGTGATAC](2), were finally performed to assess how different structural properties could affect the formation of DNA adducts. This analysis revealed that the most stable adducts of Cu(phen)(2+) and Cu(3-Clip-phen)(+) with DNA bind in the minor groove, whereas Cu(2-Clip-phen)(+) binds preferentially into the major groove.     

Density functional theory study of the photosensitization mechanisms of indigo

The triplet excited state properties and photosensitization mechanisms of indigo were investigated based on density functional theory calculations. The solvent effects on the photosensitization mechanisms of indigo have also been considered. The thermodynamic feasibility of the possible ¹O₂ and O₂·⁻-photogeneration pathways by triplet excited state indigo in different solvents was explored, in order to gain some deeper insights into the photosensitization characters of the dye.      

全氟化合物热力学性质的密度泛函理论研究

用密度泛函理论B3LYP方法,在6-31G基组水平上,对12个全氟化合物分子进行了全优化计算,得到其分子零点振动能EZPV、热能校正值Eth、恒容热容CVΦ、标准熵SΦ以及配分函数lgQ等热力学参数,并计算了这些分子的电性拓扑状态指数Em.通过最佳变量子集回归建立了电性拓扑状态指数与热力学参数之间的QSPR模型,模型的相关系数R2分别为1.000,1.000,1.000,0.999和1.000,采用逐一剔除法得到的交叉验证相关系数R2cv分别为0.999,1.000,1.000,0.999和1.000,利用建构的数学模型得到热力学性质的相对平均误差分别为0.43%,0.41%,0.46%,0.41%和0.71%.从方程可以看出,F原子取代基数量是影响全氟化合物分子热力学参数大小的主要因素,检验证明所建模型具有良好的稳定性和预测能力.     

Density functional theory studies on the reagent Ph3PBr2

We report density functional theory geometry optimizations at the B3LYP/6-311G(d,p) level of theory for the title reagent. Four stationary points on the molecular potential energy surface were located and characterized. Three of these stationary points are energy minima, one a saddle point. The minima correspond to the conventional Ph3PBr2 (three-fold Br-P-Br axis with twisted phenyl rings), the ion-pair [Ph3PBr]+Br- and a four-coordinated Ph3PBr2 spoke structure that can best be described as charge transfer on account of the substantial charge transfer from the Ph3P fragment to Br2 (as determined by a standard Mulliken population analysis and other considerations). The particular saddle point found corresponds to a three-fold Br-P-Br structure with coplanar phenyl rings. Single point B3LYP/6-311+g(3d,2p) calculations were done at the stationary point geometries in order to investigate possible deficiencies in the basis set. Solvent effects for the three solvents water, dichloroethane and cyclohexane were modelled using the self consistent reaction field Onsager method at the single point B3LYP/6-311+g(3d,2p) level of theory. In the gas phase, the charge transfer complex is the most stable of the four; in solution it is the least stable.     

Stannylated allyl carbonates as versatile building blocks for the diversity oriented synthesis of allylic amines and amides

Stannylated allylic carbonates are suitable substrates for Pd-catalyzed allylic aminations. In DMF and with [allylPdCl](2) as catalyst the stannylated allyl amines formed can be directly coupled with electrophiles according to the Stille protocol, giving rise to highly functionalized building blocks in excellent yields.     

Density functional theory studies on the electronic and vibrational spectra of octaethylporphyrin diacid

The ground-state structure and electronic and vibrational spectra of octaethylporphyrin diacid (H4OEP2+) have been studied with the density functional theory. The geometrical parameters computed with B3LYP, PBE1PBE and mPW1PW91 functionals and 6-31G* basis sets are well consistent with the experimental values. Electronic absorption spectrum of H4OEP2+ has been studied with the time-dependent DFT method, and the calculated excitation energies and oscillator strengths are compared with the experimental results. The Raman and IR spectra of H4OEP2+ and the Raman spectrum of its N-deuterated analogue (D4OEP2+) were measured. The observed Raman and IR bands have been assigned based on the frequency calculations at the B3LYP/6-31G* level of theory.     

Density functional theory studies on the Raman and IR spectra of meso-tetraphenylporphyrin diacid

The vibrational spectra of meso-tetraphenylporphyrin diacid (H4TPP2+) have been studied with the density functional theory. Raman and IR spectra of H4TPP2+ and its N-deuterated analogue (D4TPP2+) are measured and compared with the computational results. Complete assignments of observed IR and Raman bands were proposed on the bases of calculation results. The DFT calculations reproduce 140 observed fundamentals with the RMS 8.6 cm-1. The computational as well as the experimental results reveal that the saddle-distortion of porphyrin macrocycle for the diacid leads to a significant effect on its vibrational spectra. Especially, several out-of-plane skeletal modes, which were either unobserved or very weak in the Raman spectra of CuTPP and H2TPP, are activated in the Raman spectra of the diacids. In addition, enhancement for the Raman bands of phenyl CC stretching modes were observed and attributed to the conjugation effect of pi-systems of the phenyl and the porphyrinato macrocycles.     

青蒿素及其衍生物抗疟活性的密度泛函理论研究

为了深入研究青蒿素及其衍生物的抗疟活性和分子结构之间的关系,运用密度泛函理论B3LYP方法,以6-31G*为基组对青蒿素及其衍生物二氢青蒿素、蒿甲醚和青蒿琥酯进行了优化计算.从分子的几何构型、NBO电荷及前线轨道能等方面分析了青蒿素及其衍生物的抗疟活性与结构之间的关系.青蒿素及其衍生物结构中的过氧桥键是其抗疟作用的活性位,O17和O_20带负电荷越多、ΔE_(LUMO-HOMO)越低、E_(HOMO)能级越高,分子的抗疟活性越强.结果表明,4种化合物的抗疟活性顺序为:青蒿素二氢青蒿素蒿甲醚青蒿琥酯,与临床实验结果相吻合.     

Density functional theory studies of N-protonation of the free base phthalocyanine

The structures and relative energies of twenty-two N-protonated species of the free base phthalocyanine (H₂Pc) have been systematically studied with the density functional theory at the B3LYP/6-31G(d) level of theory. The calculations demonstrated that the N-protonation tends to increase the N–C bonds and the C–N–C angles on the protonation sites. The inner protonation at the isoindole-nitrogen atoms causes significant out-of-plane deformation of the macrocycle, ascribed to the steric hindrance of the central cavity. The relative energies of various protonated species were calculated and compared to deduce the preferred sites for protonation. It was revealed that the outer protonation at the meso-nitrogen atoms is energetically more favorable than the inner protonation at the isoindole-nitrogen atoms. Among the studied twenty-two protonated species, the most stable one is H₆Pc⁴⁺(IS1), for which all the outer meso-nitrogen atoms are protonated. TDDFT calculations have been performed for selected species, and the results were used to analysis the UV–visible spectrum of the concentrated sulfuric acid solution of the free base phthalocyanine.     

丁基乙烯基醚和臭氧反应机理的DFT研究

本文采用BHandHLYP和MPWB1K方法结合6-31+G(d,p)基组,对臭氧与丁基乙烯基醚三种同分异构体(n-Bve、i-Bve和t-Bve)的反应机理进行了研究,优化了反应势能面上各驻点的几何构型,用内禀反应坐标(IRC)计算和频率分析方法对过渡态进行了验证.结果表明,在臭氧与丁基乙烯基醚反应中,随着丁基基团空间位阻的变化,生成OH自由基的几率发生改变.臭氧与丁基乙烯基醚之间具有较高的反应活性,二者反应很容易生成较稳定的环合中间体,且为放热反应.其中臭氧化异丁基乙烯基醚的活化能最高,臭氧化正丁基乙烯基醚的活化能最低,理论计算得到的反应势垒与相应的实验值相吻合.     

Density functional theory study on mechanisms of epoxy‐phenol curing reaction

A comprehensive picture on the mechanism of the epoxy‐phenol curing reactions is presented using the density functional theory B3LYP/ 6‐31G(d,p) and simplified physical molecular models to examine all possible reaction pathways. Phenol can act as its own promoter by using an addition phenol molecule to stabilize the transition states, and thus lower the rate‐limiting barriers by 27.0–48.9 kJ/mol. In the uncatalyzed reaction, an epoxy ring is opened by a phenol with an apparent barrier of about 129.6 kJ/mol. In catalyzed reaction, catalysts facilitate the epoxy ring opening prior to curing that lowers the apparent barriers by 48.9–50.6 kJ/mol. However, this can be competed in highly basic catalysts such as amine‐based catalysts, where catalysts are trapped in forms of hydrogen‐bonded complex with phenol. Our theoretical results predict the activation energy in the range of 79.0–80.7 kJ/mol in phosphine‐based catalyzed reactions, which agrees well with the reported experimental range of 54–86 kJ/mol. © 2014 Wiley Periodicals, Inc.     

Density functional theory studies on tautomeric stability and infrared spectra of 2-chloroadenine

The tautomeric stability and vibrational IR spectrum of 2-chloroadenine were studied using density functional theory (DFT) at B3LYP/6-31G* level. The amino N(9)H tautomer of 2-chloroadenine was predicted to be most stable. A scaled quantum mechanical (SQM) force field approach was used to calculate the vibrational frequencies of amino N(9)H form of 2-chloroadenine. The force constant scale factors were transferred from those of purine. The mean deviation between the predicted vibrational frequencies and the observed ones is 8.0 cm(-1). The results made it possible to give complete assignments of the IR spectrum of this molecule.     

Palladium-pincer complex catalyzed C-C coupling of allyl nitriles with tosyl imines via regioselective allylic C-H bond functionalization

A mechanistically new palladium-pincer complex catalyzed allylation of sulfonimines is presented. This reaction involves C-H bond functionalization of allyl nitriles under mild conditions. The reaction proceeds with a high regioselectivity, without allyl rearrangement of the product. Modeling studies indicate that the carbon-carbon bond formation process proceeds via (eta (1)-allyl)palladium pincer complex intermediates.     

Density functional theory studies on the structures and vibrational spectra of 3,6-dichlorocarbazole and 3,6-dibromocarbazole

Becke 3-Lee-Yang-Parr density functional theory (DFT) calculations using 6-311G** and 6-311G(2df,p) basis sets were carried out to study molecular structures and vibrational spectra of 3,6-dichlorocarbazole and 3,6-dibromocarbazole. The optimized geometries, vibrational frequencies, IR intensities, and Raman activities have been obtained. On the basis of B3LYP calculations, a normal mode analysis was performed to assign the vibrational fundamental frequencies according to the potential energy distributions. The computational frequencies are in good agreement with the observed results.     

Palladium-catalyzed highly regioselective and stereoselective arylation of electron-rich allylamines with aryl bromides

A palladium-catalyzed, highly efficient Heck arylation of electron-rich N,N-diprotected allylamine derivatives with a wide range of aryl bromides under ligand-free conditions has been developed. In the presence of Pd(OAc)₂ and an appropriate additive, the reaction proceeds with excellent regioselectivity and stereoselectivity, leading exclusively to the γ-arylated (E)-allylamine products in good to excellent yields. It was found that the choice of solvent, olefin, additive and temperature has an important influence on the reaction. Worthy of note is that good results were observed only when using N,N-diprotected allylamines containing carbamate moiety, and the steric properties of allylamines also have important impacts on the regiocontrol. The use of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) or HQ (hydroquinone) as the additive is also crucial for securing a faster reaction rate. This method provides a straightforward approach for the efficient synthesis of various γ-arylated, linear (E)-allylamines.     

Density functional theory studies on vibrational and electronic spectra of 2-chloro-6-methoxypyridine

The Fourier transform infrared (FTIR) and FT-Raman spectra of 2-chloro-6-methoxypyridine have been recorded in the range 3700-400 and 3700-100 cm(-1), respectively. The complete vibrational assignment and analysis of the fundamental modes of the compound was carried out using the observed FTIR and FT-Raman data. The vibrational frequencies determined experimentally were compared with the theoretical frequencies computed by DFT gradient calculations (B3LYP method) employing the 6-31G(d,p), cc-pVTZ and/6-311++G(d,p) basis sets for the optimised geometry of the compound. The geometry and normal modes of vibration obtained from the DFT methods are in good agreement with the experimental data. The normal co-ordinate analysis was also carried out using DFT force fields utilising Wilson's FG matrix method. The influence of the substituents bulky chlorine atom and the methoxy group on the spectral characteristics of the compound has been discussed. The electronic spectrum determined by TD-DFT method is compared with the observed electronic spectrum.     

Density functional theory on phase space

Forty‐five years after the point de départ [Hohenberg and Kohn, Phys Rev, 1964, 136, B864] of density functional theory, its applications in chemistry and the study of electronic structures keep steadily growing. However, the precise form of the energy functional in terms of the electron density still eludes us—and possibly will do so forever [Schuch and Verstraete, Nat Phys, 2009, 5, 732]. In what follows we examine a formulation in the same spirit with phase space variables. The validity of Hohenberg–Kohn–Levy‐type theorems on phase space is recalled. We study the representability problem for reduced Wigner functions, and proceed to analyze properties of the new functional. Along the way, new results on states in the phase space formalism of quantum mechanics are established. Natural Wigner orbital theory is developed in depth, with the final aim of constructing accurate correlation‐exchange functionals on phase space. A new proof of the overbinding property of the Müller functional is given. This exact theory supplies its home at long last to that illustrious ancestor, the Thomas–Fermi model. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Density functional theory and post-Hartree-Fock studies on molecular structure and harmonic vibrational spectrum of formaldehyde

Density functional theory (DFT) with the Becke's three-parameter exchange correlation functional and the functional of Lee, Yang and Parr, gradient-corrected functionals of Perdew, and Perdew and Wang [the DFT(B3LYP), DFT(B3P86) and DFT(B3PW91) methods, respectively], and several levels of conventional ab initio post-Hartree-Fock theory (second- and fourth-order perturbation theory M?ller-Plesset MP2 and MP4(SDTQ), coupled cluster with the single and double excitations (CCSD), and CCSD with perturbative triple excitation [CCSD(T)], configuration interaction with the single and double excitations [CISD], and quadratic configuration interaction method [QCISD(T)], using several basis sets [ranging from a simple 6-31G(d,p) basis set to a 6-311+ +G(3df, 2pd) one], were applied to study of the molecular structure (geometrical parameters, rotational constants, dipole moment) and harmonized infrared (IR) spectrum of formaldehyde (CH₂O). High-level ab initio methods CCSD(T) and QCISD(T) with the 6-311+ +G(3df, 2pd) predict correctly molecular parameters, vibrational harmonic wavenumbers and the shifts of the harmonic IR spectrum of ¹²CH₂ ¹⁶O upon isotopic substitution. Received: 30 January 1997 / Accepted: 7 May 1997