Experimental and DFT study of the aza-Diels-Alder reaction between cyclopentadiene and protonated benzylimine derivated from glyoxylates

The Diels-Alder reaction of protonated N-benzyl imine of methyl glyoxylate with cyclopentadiene in different solvents gave mixtures of exo/endo adducts. The exo/endo selectivity of the reaction was elucidated by NMR experiments. Theoretical calculations by means of density functional theory (DFT) at the B3LYP/6-31G(d) level have also been performed to elucidate the molecular mechanism of this reaction. The DFT results suggest a highly asynchronous concerted mechanism, which in turn can explain the preferred exo stereoselectivity of the reaction. Inclusion of solvent effects enhances the exo selectivity, and this effect increases with the polarity of the solvent, in good agreement with the experimental findings.     

DFT Study on the Structural, Electronic, and Spectroscopic Properties of the Highest Epoxygenated Fullerene C36O18

Theoretical investigation on the highest epoxygenated fullerene C36O18 formed from the initial C36 fullerene with D6h symmetry has been performed at the B3LYP/6-31G(d) level. Their equilibrium structures, thermal stabilities, electronic structures, vertical ionization potentials, vertical electron affinities, vibrational frequencies and 13C NMR chemical shifts have been studied. The calculation results showed that C36O18 isomers have higher LUMO-HOMO energy gaps than the fullerene C36 and should be more stable. Compared with C36 , it is less possible for C36O18 to accept or donate electrons from reduced VEAs and enhanced VIPs. It has been found that C36O18 isomers are not aromatic at all or antiaromatic on analyzing the NICS values. The present study will encourage further theoretical and experimental analyses of this system in future.     

Structure and stability of B+13 clusters

The structures and energies of B⁺₁₃, observed experimentally to be an unusually abundant species among cationic boron clusters, have been studied systematically with B3LYP/6–31G* density functional theory. The most thermodynamically stable B⁺₁₂ and B⁺₁₃ clusters are confirmed to have planar or quasiplanar rather than globular structures. However, the computed dissociation energies of the 3-dimensional B⁺₁₃ clusters are much closer to the experimental values than those of the planar or quasiplanar structures. Hence, planar and 3-dimensional B⁺₁₃ may both exist. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 203–214, 1998     

二氯甲基硅烷醇解的量化计算

采用溶剂法和B3LYP/6-31G(d)基组研究了甲基含氢二氯硅烷的醇解反应.结果表明，反应分二步进行，其一步和二步醇解均为放热反应，并得出了反应的最佳温度、醇与硅烷的最佳配比、最佳进样方式、主反应和副反应的活化能及其可能的反应途径曲线.计算结果和实验结果较为一致.     

2,2-二氟-1-溴-1-锂乙烯的结构及重排反应的理论研究

用量子化学中的密度泛函DFT方法,在B3LYP／6-31G(d,p)水平上研究了2,2-二氟-1-溴-1-锂乙烯F2C—CLiBr的结构．结果表明,F2C=CLiBr有2种平衡结构,其中只有1种是稳定的．对稳定的平衡结构,找到了其可能的重排反应过渡态,根据计算得到的重排反应势垒,解释了氟原子只从溴原子对位发生迁移的原因．     

DFT Study on the Heterofullerene C48O12 with Rare Th Symmetry

The molecule with T_h symmetry is rare. A novel C60-like molecule C48O12 with rare Th symmetry has been studied at the B3LYP/6-31G(d) level of theory. Its structural, electronic, vibrational, NMR, and thermodynamic properties have been calculated at the B3LYP/6-31G(d) level of theory. Vibrational modes have been assigned according to their symmetry. There are 73 independent vibrational modes: 22 IR-active modes with T u symmetry and 37 Raman-active modes with Ag , Eg and Tg symmetry, respectively. The heat of formation has been calculated by using isodesmic reactions, 765.7 kJ mol-1 . According to the heat of formation and the HOMO-LUMO gap, C48O12 with rare Th symmetry is more stable than C60 .     

基于不同功能的苯并噻二唑为受体单元和低聚噻吩为给体单元的D-A-D-A-D型有机小分子光伏材料的理论计算研究

设计了四个以四联噻吩为中心给电子单元,联二噻吩为末端给电子单元,不同功能的苯并噻二唑(DOBT,BT,FBT和FFBT)为吸电子单元的有机小分子太阳能电池给体材料,分别称为DOBT-8T,BT-8T,FBT-8T和FFBT-8T.在B3LYP/6-31G(d)基组的水平上利用密度泛函和含时密度泛函理论对四个小分子进行了理论计算.详细分析了吸电子单元苯并噻二唑的结构修饰对小分子给体材料性能的影响.理论计算结果显示,不同功能的苯并噻二唑单元的引入对小分子给体材料的几何结构、禁带宽度、HOMO与LUMO能级、轨道电子密度分配、能量驱动力、开路电压和分子中的原子电荷(NPA)都有重要调节作用.相比于其它分子,以FBT为吸电子单元的FBT-8T,显示了最窄的带隙和较低的HOMO能级值.以FFBT为吸电子单元的FFBT-8T,获得了最低的HOMO能级和较为合适的禁带宽度.利用Scharber模型分别计算了基于小分子/PC61BM为活性层的光伏器件的能量转换效率(PCE),基于FBT-8T/PC61BM和FFBT-8T/PC61BM的光伏器件,将获得的PCE分别高达约4.7%和5.2%.在以上研究的基础上,推测FBT-8T和FFBT-8T是潜在的高性能的有机小分子体异质结光伏给体材料.     

DFT Studies on Thermal Stabilities,Electronic Structures,and ~（13）C Chemical Shifts of C_（24）O_2 Based on Fullerene C_（24）（D_6）

Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 (D6) and C24O have been performed using density functional theory (DFT) method. The geometric and electronic structures as well as the relative energies and thermal stabilities of various C24O2 isomers at the ground state have been calculated at the B3LYP/6-31G(d) level of theory. And the 1,4,2,5-C24O2 isomer was found to be the most stable geometry where two oxygen atoms were added to the longest carbon-carbon bonds in the same pentagon from a thermodynamic point of view. Based on the optimized neutral geometries, the vertical ionization potential and vertical electron affinity have been obtained. Meanwhile, the vibrational frequencies, IR spectrum, and 13C chemical shifts of various C24O2 isomers have been calculated and analyzed.     

DFT Study on the Bilayer Pentaprismane C15H10

1INTRODUCTIONInrecentyears,agreatnumberofachievementshavebeenacquiredforthemoleculeswithcage-likestructures,suchasfullerenesandpolyhedralhydro-carbon.Pentaprismane,firstlysynthesizedbyEaton,OrandBranca[1]in1981,isatypicalpolyhedralhy-drocarbon.Owingtoitssymmetricalandstrainedstructure,manystudiesincludingMM2andMM3molecularmechanicscalculations[2,,semi-empiri-3]calMNDOandAM1molecularorbitalcalcula-tions[4],abinitioHFcalculations[5～7]andDFTcal-culation[8]havebeencarriedoutonit.Recen…     

DFT Study on the Electronic and Structural Properties of ReO5-/0 Clusters

The electronic and structural properties of ReO5 and ReO5 clusters are investigated using density functional theory (DFT) calculations. The lowest energy structures for both the anionic and neutral clusters are determined, and the corresponding photoelectron spectrum is simulated. Our results show that ReO5 can be described as an unusual peroxo molecule, Re(O)3(η2-O2) , while ReO5 is found to be exhibiting the O2 o radical character. Molecular orbital analyses and spin density analyses are performed to elucidate the chemical bonding and the electronic and structural properties in these two rhenium oxide clusters.     

Photo‐physical Properties of N‐methyl‐3,4‐fulleropyrrolidine and Its Derivatives: A DFT and TD‐DFT Investigation

A series of N‐methyl‐3,4‐fulleropyrrolidine (NMFP) derivatives were designed by selecting different π‐conjugated linkers and electron‐donating groups as D‐π‐A and D‐A systems. The optimised structures and photo‐physical properties of NMFP and its derivatives have been determined using density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods with the B3LYP functional and the 6‐31G basis set. According to the computation analysis, both the π‐conjugated linkers and the electron‐donating groups can influence the electronic and photo‐physical properties of the NMFP derivatives. Our calculated results demonstrated that the electron‐donating groups, with significant electron‐donating ability, had the tendency to increase the highest occupied molecular orbital (HOMO) energy. The π‐conjugated linkers with lower resonance energy decreased the lowest occupied molecular orbital (LUMO) energy and caused a significant decrease in the energy gap (E_g) between the E_HOMO and E_LUMO. A Natural Bond Orbital (NBO) analysis examines the effect of the electron‐donating group, π conjugated linker, and electron‐withdrawing group for these NMFP derivatives. For the NMFP derivatives, a projected density of state (PDOS) analysis demonstrated that the electron density of HOMO and LUMO are concentrated on the electron‐donating group and the π‐conjugated linker, respectively. A TD‐DFT/B3LYP calculation was performed to calculate the electronic absorption spectra of these NMFP derivatives. Both the electron‐donating group and the π‐conjugated linker contribute to the major absorption peaks, which are assigned as HOMO to LUMO transitions and are red‐shifted relative to those of non‐substituted NMFP.     

The Combination and Disproportionation of Ethyl,n-Propyl,and sec-Propyl Radicals: A DFT Study

Density functional theory (B3LYP) has been applied to the problem of free radical combination and disproportionation reactions. These have been examined for the ethyl, n-propyl, and sec-propyl radicals. For the combination reactions, the enthalpy of activation fell in the range of 5 to 7 kcal/mol, which is within the limits of computational error. The transition structure of disporportionation reaction each displayed a bent C...H...C angle for the transfer of the hydrogen in contrast to earlier reports done at the semiempirical level. The activation enthalpies for the hydrogen transfer process increased with the number of attached methyl groups on the donor radical.     

戊烯自由基阳离子的密度泛函理论研究

使用密度泛函理论B3LYP方法和6-31G(d,p)、6-31＋G(d,p)、6-311G(d,p)及6-311＋G(d,p)基组，分别对2-C5H10＋和1-C5H10＋的各种构象进行了几何构型优化，并用B3LYP/6-311G(d,p)进行了频率分析计算.计算预言1-C5H10＋具有非平面构型，与以往报导的从头算计算结论相反.在两个自由基阳离子的各种构象的B3LYP几何构型上，进行了B3LYP和UMP2(full)方法的超精细偶合常数计算，得到了比以往更好的结果.     

呋喃分子链式加聚物(C4H4O)n(n = 1～8)的密度泛函理论研究

采用B3LYP/6-31G方法对呋喃分子链式加聚物(C4H4O)n(n=1~8)体系进行了全优化,在进行结构优化的同时得到链式加聚物的总能量(ET)、零点能(ZPE)、热容(opC)和熵(oS)。通过对体系的能量分析,确定得到的结构是体系的稳定构型;分析了ZPE、opC和oS与n的关系,并在能量的基础上得到呋喃分子以不同方式聚合成链式加聚物时的生成焓,并由此确定链式加聚物系列的聚合过程和相对稳定性。     

Site-selective formation of N-arylmethylimidazoles and C-arylimines in the reaction of 4,5-diamino-2,1,3-benzothiadiazole with aromatic aldehydes

Regioselective formation of N-arylmethylimidazoles and C-arylimines was found in the reaction of 4,5-diamino-2,1,3-benzothiadiazole with selected aromatic aldehydes. The regiochemistry of the reaction products was confirmed by single crystal X-ray analysis. Gibbs free energy calculation using DFT method at the B3LYP/6-31G(d) level supports the regio-selectivity observed. The 4-imine obtained in the reaction of 4,5-diamino-2,1,3-benzothiadiazole with pyrene-1-carboxaldehyde showed an unusually low magnetic field shift of the imine proton that was reproduced by molecular calculations.     

Facile Separation,Spectroscopic Identification,and Electrochemical Properties of Higher Trifluoromethylated Derivatives of [70]Fullerene

We survey the structure and electronic properties of the family of higher trifluoromethylated C₇₀(CF₃)_n molecules with n=14, 16, 18, and 20. Twenty‐two available compounds, of which thirteen are newly obtained and characterized, demonstrate the broad diversity of π‐system topologies, which enabled us to study the interplay between the CF₃ addition pattern and the electronic properties. UV/Vis spectroscopic and cyclic voltammetric studies demonstrate the importance of the exact addition pattern rather than the plain number of addends. Of particular interest is the skew pentagonal pyramid (SPP) addition pattern, which enables formation of closed‐shell cyclopentadienyl anions C₇₀(CF₃)_{n? 1} ^? through CF₃ detachment upon electron transfer. A detailed study of the process is presented for a SPP‐C₇₀(CF₃)₁₆ where potentiostatic electrolysis at the second reduction potential gives C₇₀(CF₃)₁₅^? oxidizable to a persistent C₇₀(CF₃)₁₅^· radical. Together with the literature data for the lower C₇₀(CF₃)_n compounds with n=2–12, the present results show good correlation between the experimental boundary level positions and the DFT predictions. The compounds turn out to be electron acceptor molecular semiconductors with experimental LUMO energies and HOMO–LUMO gaps within the ranges of ?4.3 to ?3.7 eV and 1.6 to 3.3 eV, respectively, depending on the shape of the conjugated fragments. The HOMO levels fall within the range of ?5.6 to ?6.9 eV and show linear correlation with the number of addends.     

1－甲氧基－1－锂乙烯的结构及其分解反应的DFT研究

用量子化学中的密度泛函DFT方法，在B3LYP／631G（d,p）水平上研究了－甲 氧基－1－锂乙烯的结构。结果表明，1－甲氧基－1－锂乙烯有4种平衡结构，其中 只有1种是稳定的。对稳定的平衡结构，找到了分解反应的过渡态。在得到分解反 应过渡态的基础上，根据Eyring过渡态理论，计算了不同温度下1-甲氧基－1-钾乙 烯分解反应的速率常数，并根据速率常数计算了其平均寿命τ，根据平均寿命τ讨 论这类物质的稳定性问题。     

Comparative analysis of a full-electron basis set and pseudopotential for the iodine atom in DFT quantum-chemical calculations of iodine-containing compounds

A systematic study was performed to examine the possibilities of the B3LYP DFT method in a dgdzvp full-electron basis and of the method including a pseudopotential for iodine compounds. The full-electron basis generally gives better agreement for X-I bond lengths and reaction enthalpies of iodination of organic compounds and equally good agreement in calculations of the IR vibrations of the X-I bond length compared with the studies using the pseudopotential. The full-electron basis also allows adequate calculations of the quadrupole coupling constants of iodine atoms and is generally characterized by smaller computing times.