Electronic and Spectroscopic Properties of La2@C112 Isomers

Among the 3352 isolated pentagon rule(IPR) isomers and 129073 non-IPR isomers satisfying adjacent pentagon pairs(APPs) ≤ 2 of fullerene C₁₁₂, the lowest-energy IPR and non-IPR isomers of C₁₁₂ and C₁₁₂^6- have been fully screened by the density functional tight-binding(DFTB) and density functional theory(DFT) methods for stu-dying the electronic and spectroscopic properties of La₂@C₁₁₂. The structural features and infrared and absorption spectra of those isomers were analyzed in detail, and the characteristic fingerprint absorption peaks were assigned. To clarify the relative stabilities of La₂@C₁₁₂ isomers at high temperature, entropy contributions were determined at the B3LYP level. IPR isomer La₂@C₁₁₂(C₂:860136) is not the lowest-energy isomer but is one of the most important isomers. This is the first work that considers non-IPR C₁₁₂ isomers when exploring the structure and properties of La₂@C₁₁₂.     

Pyridyl 'ring-flipping' in the dimers [Me2E(2-py)]2 (E=B, Al, Ga; 2-py=2-pyridyl)

The boron and aluminium dimers [Me2E(micro-py)]2 [E=B (1); Al (2)] are formed as mixtures of two isomers in which the group 13 centres are coordinated by the bridging 2-py ligands in a cis or trans manner, however, in contrast to previous studies, we find that simply heating the mixtures of these isomers of and gives the more thermodynamically stable (synthetically useful) trans isomers exclusively (the trans isomer being the only product in the case of the gallium analogue ).     

Structures, stabilities, electronic, and optical properties of C64 fullerene isomers, anions (C64(2-) and C64(4-)), metallofullerene Sc2@C64, and Sc2C2@C64

The 3465 classical isomers of C(64) fullerene have been investigated by quantum chemical methods PM3, and the most stable isomers have been refined with HCTH/3-21G//SVWN/STO-3G, B3LYP/6-31G(d)//HCTH/3-21G, and B3LYP/6-311G(d)//B3LYP/6-31G(d) level. C(64)(D(2):0003) with the lowest e(55) (e(55) = 2), the number of pentagon-pentagon fusions, is predicted to be the most stable isomer and it is followed by the C(64)(C(s):0077) and C(64)(C(2):0103) isomers within relative energy of 20.0 kcal/mol. C(64)(D(2):0003) prevails in a wide temperature range according to energy analysis with entropy contribution at B3LYP/6-31G(d) level. The simulated IR spectra and electronic spectra help to identify different fullerene isomers. All the hexagons in the isomers with e(55) = 2 display local aromaticity. The relative stabilities of C(64) isomers change with charging in ionic states. Doping also affects the relative stabilities of fullerene isomers as demonstrated by Sc(2)@C(64)(D(2):0003) and Sc(2)@C(64)(C(s):0077). The bonding of Sc atoms with C(64) elongates the C-C bond of two adjacent pentagons and enhances the local aromaticity of the fullerene cages. Charging, doping, and derativization can be utilized to isolate C(64) isomers through differentiating the electronic and steric effects.     

Ab initio investigation of the potential energy surfaces of C2H2F2 and C2H2F2+

Ab initio MO calculations have been performed for neutral and cationic C₂H₂F₂ structures. Olefinic and carbene structures are investigated for the neutral isomers, while olefinic, carbene, and fluoronium-type cations are found. Stability orders and rotational barriers are discussed in terms of orbital and Coulomb interaction. Contrary to previous studies, the higher stability of the geminal isomers is interpreted to be caused by Coulomb attraction.     

Theoretical study of isomerism in the molecules N2O,PNO, P2O,N2S,PNS, and P2S

We have carried out nonempirical calculations of the potential surface for isomeric rearrangements of the molecules N₂O, N₂S, PNO, PNS, P₂O, and P₂S. It was found that for the molecules N₂O and N₂S a linear structure is considerably more favorable than a cyclic one, which lies 60 kcal·mole^–1 higher and has low stability. For P₂O and P₂S the linear and cyclic isomers have similar energies. For PNO and PNS there are two linear isomers and one cyclic isomer. The isomers are separated by appreciable barriers and can exist independently. It is predicted for the ABC molecules with 16 valence electrons that if two or all three of the atoms belong to the third or a later period, then the cyclic isomers should be favored to at least the same extent as the linear isomers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 794–802, April, 1990.     

A DFT study on the dimerization of C62, H2-C62, and F2-C62

On the basis of calculations using the density functional theory, we show that C(62), a recently synthesized nonclassical fullerene, will presumably undergo dimerization with various isomers at elevated temperatures. This is shown by calculating the dimerization energy and the activation barrier of the dimerization. Eight possible isomers of the dimer were identified, all of which are more stable than the two isolated monomers. The relative stability of various isomers depends upon the kind of C=C bonds within the four-membered carbon ring involved in the dimerization. In addition, similar calculations were performed for the monomers and dimers of H(2)-C(62) and F(2)-C(62). Six isomers were identified for each of the dimers. Although less pronounced than the case of the C(62) dimer, all isomers of the H(2)-C(62) dimer are appreciably more stable than the individual monomers. Although a large steric repulsion due to F atoms significantly reduces the stability of F(2)-C(62) dimer, its two isomers are still more stable than separate monomers.     

三重态SiCP2异构体的结构和稳定性的理论研究

采用DFT,QCISD和CCSD(T)等理论计算方法对三重态SiCP2异构体的结构和稳定性进行了理论研究.在B3LYP/6-311G(d)水平下,共计算得到由17个过渡态相连接的15个异构体.在CCSD(T)/6-311 +G(2df)//QCISD/6-311G(d)水平下,考虑重点振动能相对能量最低的三元环状异构体P-cCSiP 8(0.0 kJ/mol)及四元环状结构的cPCSiP 4具有相当大的动力学稳定性,在一定的实验室和星际条件下可能被检测到.另外,对它们的成键性质也进行了分析.     

Excited electronic states of the cyclic isomers of O2 and SO2

The low-lying electronic states of O3 and SO2 in their bent and cyclic isomers up to about 10 eV are calculated using the multireference configuration interaction (MRCI) method with a standard Gaussian correlation consistent polarized triple-zeta (cc-pVTZ) basis set. The vertical excitation energies, electron configurations, and oscillator strengths of these states are reported. The molecular orbital structures and excited states of the cyclic isomers are discussed in relation to the bent ones. Coherent anti-Stokes Raman spectroscopy (CARS) schemes for detecting the synthesis of the cyclic isomers are suggested.     

Synthesis and structure of 2-ethoxy- and 2-aminomethylidene-3-fluoroalkyl-3-oxopropionates

Condensation of ethyl 3-polyfluoroalkyl-3-oxopropionates with excess triethyl orthoformate gave ethyl 3-polyfluoroalkyl-2-ethoxymethylidene-3-oxopropionates which reacted with primary aliphatic, aromatic, and heterocyclic amines to form ethyl 2-alkyl(aryl, hetaryl)aminomethylidene-3-polyfluoroalkyl-3-oxopropionates. According to the X-ray diffraction and IR data, the latter exist in the crystalline state as the corresponding E isomers, while in solution (NMR data), as mixtures of Z and E isomers. Condensation of ethyl 2-ethoxymethylidene-3-oxopropionates with secondary heterocyclic amines (morpholine and pyrrolidine) led to the formation of 2-morpholino(pyrrolidin-1-yl)methylidene-3-fluoroalkyl-3-oxopropionates which were shown to exist as Z isomers both in the crystalline state and in solution.     

Si_2C_(m-2)(m=4～15)团簇的结构与稳定性

用密度泛函理论(DFT)的B3LYP/6-31G*方法, 对Si2Cm-2(m = 4~15)团簇的几何构型、电子结构、振动频率等性质进行了研究, 讨论了化学键的特征和热力学稳定性, 比较了Si2Cm-2团中环状和线状结构的差异。结果表明, m = 4~13的团簇为线状结构, m=14~15的团簇为环状结构。在线状结构中, 随着m增大, 自旋多重度出现1、3交替变化, 并且Si原子倾向于在C链端部成键;环状结构中, C原子形成环状, 2个Si原子处于椭圆环状构型的两端。m 为奇数的Si2Cm-2团簇比m为偶数的更为稳定。     

Synthesis and characterization of bispyrrolidine derivatives of H2@C60: differentiation of isomers using 1H NMR spectroscopy of endohedral H2

Bisadduct isomers of a H(2)@C(60) derivative with nitroxide addends have been synthesized, isolated and characterized. The (1)H NMRs of endohedral H(2) of the major isomers show well-separated chemical shifts, which could be useful for structural assignment and identification of the purity of the C(60) bisadduct isomers.     

2-氨基-3-硝基吡啶和2-氨基-5-硝基吡啶的EI/MS/MS分析

2 氨基 3 硝基吡啶和2 氨基 5 硝基吡啶的一级质谱图接近,单纯通过一级质谱图较难区分这两种异构体,利用离子阱质谱的串联质谱技术对2 氨基 3 硝基吡啶和2 氨基 5 硝基吡啶在离子阱内以He作碰撞气进行碰撞诱导裂解,所得的二级质谱图表明,两者之间存在明显的差别,可用于2 氨基 3 硝基吡啶和2 氨基 5 硝基吡啶的鉴别。     

NC2S+离子的结构和稳定性的理论研究

在密度泛函和从头算理论水平下计算了单重态的NC2S+离子的结构、能量、光谱以及稳定性. 在B3LYP/6-311G(d)水平下, 得到8个异构体, 它们由15个过渡态相连接. 在CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE水平下, 得到能量最低的异构体是直线型的具有1Σ电子态的NCCS+(1)(0.0 kJ/mol), 其次是直线型的异构体CNCS+(2)(54.8 kJ/mol). 两个低能量的异构体1和2及另外一个高能量的直线型异构体CCNS+(3)(323.8 kJ/mol)都具有相当大的动力学稳定性, 这三个异构体在具备一定条件的实验室和星际条件下是可以进行观测的. 分析了这3个异构体的成键性质.     

Regioselective sulfonation of 2-porphyrinylthiophene under kinetic and thermodynamic control

Sulfonation of meso-tetra(thien-2′-yl)porphyrin with concentrated sulfuric acid was found to produce several tetrasulfonated meso-tetra(thien-2′-yl)porphyrin isomers, where sulfonic acid groups were substituted at the 5- or the 4-positions of the thienyl groups, and the tetrasodium salts of the isomers were successfully isolated by reversed-phase HPLC. Temperature dependence of the production ratio of the isomers revealed that sulfonation reactions at the 5- and the 4-positions of 2-porphyrinylthiophene occur under kinetic and thermodynamic control, respectively.     

2-氨基-3-硝基吡啶和2-氨基-5-硝基吡啶的CI-MS-MS分析

二氨基-3-硝基吡啶和2_氨基-5-硝基吡啶的EI—MS质谱图接近，单纯通过Ⅱ-MS质谱图较难区分这两种异构体，作者以甲烷为反应气对2-氨基-3-硝基吡啶和2-氨基-5-硝基吡啶进行化学电离，并利用离子阱质谱的串联质谱技术在离子阱内以He作碰撞气进行碰撞诱导裂解，所得的CI—MS—MS质谱图表明，两者之间存在明显的差别，可用于2-氨基-3-硝基吡啶和2-氨基一5一硝基吡啶的鉴别。     

Theoretical study of isomerism of compounds of N2 and N2H2 molecules with aluminum clusters Al13 and Al12Ti

Segments of the potential energy surfaces corresponding to successive elementary stages of multistep fragmentation of nitrogen and diimine molecules upon their reaction with the aluminum cluster Al₁₃ and its doped analogue Al₁₂Ti have been calculated by the density functional theory method. The minimum energy pathways of these reactions have been calculated for the stages of physisorption, chemisorption, and N₂ and N₂H₂ fragmentation with different ways of insertion of fragments into the Al₁₃ and Al₁₂Ti cages. Relative energies, structural characteristics, and vibrational frequencies of coordinated and fragment isomers have been calculated, the barriers separating these isomers have been evaluated, and molecular diagrams of the reactions have been constructed. The effect of doping on the relative energies of intermediates and activation barriers has been considered. A conclusion has been drawn that doping with titanium should facilitate the reactions of molecular nitrogen with aluminum clusters. Unusual isomers with a five- and six-coordinate nitrogen atom N* have been localized. The results are compared with the data of analogous previous calculations of the PES of isomers corresponding to stepwise fragmentation of an acetylene molecule in related Al₁₃C₂H₂ and Al₁₂TiC₂H₂ derivatives.     

Theoretical study on stability and properties of NC2O isomers

The structures, energetics, spectroscopies, and stabilities of the doublet NC(2)O radical are explored at density functional theory and ab initio levels. Nine minimum isomers are located connected by 22 interconversion transition states. At the CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest-lying isomer is bent NCCO 1 (0.0 kcal/mol) with (2)A' state followed by bent isomer CNCO 2 (16.7). Two isomers (1 and 2) and another high-lying species CCNO 4 (99.4) with bent structure are considerably stabilized by a barrier of at least 20 kcal/mol. All of the three isomers should be experimentally or astrophysically observable. This result is consistent with their indication of neutralization-reionization mass spectrometry experiments. Also, the calculated spectroscopic properties and bond distances of known NCCO 1 are consistent with recent experimental observations and theoretical studies. The bonding natures of the isomers 1, 2, and 4 are analyzed. Their molecular properties including the heats of formation, adiabatic ionization potentials, and adiabatic electronic affinities are calculated at the higher levels G3//B3LYP, G3(MP2)//B3LYP, QCISD, and CCSD(T) (single-point). Possible formation strategies of the isomers 1, 2, and 4 in laboratory and space are also discussed in detail.     

C_(59)F_(2n)HN(n=1,2)异构体的结构与稳定性的理论研究

分别用MNDO和AM1两种半经验方法,对C59F2nHN (n = 1, 2) 的异构体进行几何构型全优化,结合频率分析及HF/6-31G单点能计算,确定了各异构体的基态结构及其相对稳定性。计算结果表明,C59HN的F加成物的立体选择性规律与C60的不同,最稳定异构体不是1-2加成物。C59F2HN的最稳定异构体是1-4加成的6, 18-或12, 15-异构体; C59F4HN的最稳定异构体是1-4,1-4加成的6, 18; 12, 15-异构体,其能量远小于其它各异构体的能量。N原子取代碳笼骨架C原子后,改变了碳笼F加成物的立体选择性规律。     

Esters of 2,5-multisubstituted-1,3-dioxane-2-carboxylic acid: their conformational analysis and selective hydrolysis

The carbomethoxy group at the C2 position of the 2,5-multisubstituted 1,3-dioxanes prefers the axial conformation rather than the equatorial one due to an anomeric effect. The trans isomers of the 5-monosubstituted compounds are more selectively hydrolyzed than the cis isomers. Based on the calculated results, hydrolysis to the trans isomers is attributed to the larger carbonyl charges of the trans than those of the cis isomers. The anomeric and homoanomeric effects will explain the axial preference of the carbomethoxy group and selective hydrolysis to the trans isomers. Furthermore, the calculated stability between the cis and trans isomers is in good agreement with the experimental results in the equilibrium state.     

Double silyl migration converting ORe[N(SiMe(2)CH(2)PCy(2))(2)] to NRe[O(SiMe(2)CH(2)PCy(2))(2)] substructures

The reaction of (R(2)PCH(2)SiMe(2))(2)NM (PNP(R)M; R = Cy; M = Li, Na, MgHal, Ag) with L(2)ReOX(3) [L(2) = (Ph(3)P)(2) or (Ph(3)PO)(Me(2)S); X = Cl, Br] gives (PNP(Cy))ReOX(2) as two isomers, mer,trans and mer,cis. These compounds undergo a double Si migration from N to O at 90 degrees C to form (POP(Cy))ReNX(2) as a mixture of mer,trans and fac,cis isomers. Additional thermolysis effects migration of CH(3) from Si to Re, along with compensating migration of halide from Re to Si. DFT calculations on various structural isomers support the greater thermodynamic stability of the POP/ReN isomer vs PNP/ReO and highlight the influence of the template effect on the reactivities of these species.