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。     

C59XH(X=N,B)自由基加成区域选择性的理论研究

用半经验的AMl方法,对C59XHCl2n(X=N,B;n=1～2)和C60H2Cl2n(n=1～2)的异构体进行几何构型全优化和振动频率计算,结合密度泛函B3LYP／6—31G^*单点能计算确定各异构体的相对稳定性．对比C59XH(X=N,B)和C60H2的H2加成方式,计算结果表明H2或Cl2加在碳笼官能化部分的邻近位置在能量上都是有利的：C59NH和C59BH自由基多加成物区域选择性的差别可归因于N原子和B原子电子性质的不同;立体效应是导致H2和Cl2加成方式不同的主要原因．     

C59XH (X＝N, B)自由基加成区域选择性的理论研究

用半经验的AM1方法, 对C₅₉XHCl_2n (X＝N, B; n＝1～2)和C₆₀H₂Cl_2n (n＝1～2)的异构体进行几何构型全优化和振动频率计算, 结合密度泛函B3LYP/6-31G*单点能计算确定各异构体的相对稳定性. 对比C₅₉XH (X＝N, B)和C₆₀H₂的H₂加成方式, 计算结果表明H₂或Cl₂加在碳笼官能化部分的邻近位置在能量上都是有利的; C₅₉NH和C₅₉BH自由基多加成物区域选择性的差别可归因于N原子和B原子电子性质的不同; 立体效应是导致H₂和Cl₂加成方式不同的主要原因.     

富勒烯衍生物(C36OH)+异构体间的相互转化机理──羟基(OH)的分子内迁移

用从头算HF/STO-3G方法对(C36OH)+的3种异构体之间的重排机理进行了理论研究.计算结果表明,异构体2的热力学稳定性最强;从动力学角度考虑,由异构体1和3转化为2比反方向转化容易得多.结合电荷在碳笼表面的分布,预计动力学上最终在C7和C26位置上发生羟基加成的几率最大,该结论与热力学上预计的跨赤道六元环内羟基1,4-加成所得到的C36(OH)2异构体最稳定的结果一致.     

C78(CH2)2结构和光谱的半经验和密度泛函研究

用INDO系列方法研究C₇₈(CH₂)₂的18种可能异构体，表明最稳定异构体是42,43,62,63-C₇₈(CH₂)₂,其中CH₂加在C₇₈（C_2V）椭球长轴所穿过的同一六员环的两个6/6键上，形成类环丙烷结构。并对最稳定的四种异构体用B3LYP/3-21G方法进行了结构优化,在此基础上, 用INDO/CIS方法计算的C₇₈(CH₂)₂稳定异构体的电子光谱的第一吸收峰和用AM1方法计算的碳笼上的C-C键的主要红外振动频率与C₇₈（C_2V）相比发生兰移，原因是C₇₈(CH₂)₂具有较大的LUMO-HOMO能隙和由于加成带来的共轭体系变小。在B3LYP/3-21G水平上计算的¹³C NMR谱表明,被加成的C-C键上的C原子化学位移向高场移动, 这是因为sp²杂化的C 原子被转化为 sp³杂化的C 原子.     

C36H2异构体的稳定性及其加成位置选择性的研究

使用AM1和PM3两种半经验方法,对所有的C₃₆H₂异构体实行非对称性限制的全优化,并结合频率分析及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.在此基础上,通过分析加成位置与异构体稳定性之间的关系,得出三条加成位置选择性的规律.最后,利用π-轨道轴矢量(POAV)方法计算了反应前后碳笼中张力的变化.张力与键级分析的结果表明加成位置选择性的规律不是由碳笼释放的张力决定的,而是由C₃₆H₂体系的总共轭性质决定的.     

富氧条件下Cu/Al2O3催化剂上C3H6选择性还原NO的研究

以Cu/Al2O3为催化剂,对富氧条件下C3H6为还原剂选择性催化还原NO反应进行了研究.活性评价结果表明,与高活性的Ag/Al2O3催化剂相比,Cu/Al2O3催化剂选择性还原NO的活性较低,NO的最高转化率仅为40%.在所考察的温度范围(473～723K)内,红外谱图中不存在有机含氮化合物(R—ONO和R—NO2)的特征振动吸收峰.作为反应中间体—NCO的前驱体,有机含氮化合物在Cu/Al2O3催化剂表面难以生成是造成催化剂选择性还原NO活性低的直接原因.在Cu/Al2O3催化剂上,NO2吸附能够优先发生,并以NO3-物种的形式覆盖在大部分催化剂表面.动态原位红外光谱实验发现,这种NO3-表面物种与C3H6的反应性较差,使生成有机含氮化合物的关键反应难以发生,但此时的催化剂表面有利于C3H6和O2的完全氧化反应,这是导致Cu/Al2O3催化剂选择性较低的根本原因.     

C70S可能异构体的结构与稳定性的理论研究

分别用半经验的AMl，PM3及MNDO方法研究了富勒烯衍生物C70S的12种可能异构体的结构和稳定性．计算结果表明：S原子加成在4种6-6键上的稳定构型中，非赤道带6-6键加成的三个异构体为闭环结构，赤道带6-6键加成的一个异构体为开环结构；S原子加成在4种6-5键上均可产生开环和闭环两种稳定构型．加成在6-5双键的异构体其闭环构型更稳定，加成在6-5单键的异构体其开环构型更稳定．闭环异构体中S原子加成在碳球极处6-6键上的构型1，2最稳定，开环异构体中S原子加成在赤道带6-6键上的构型8最稳定．     

自由基C59N及双体(C59N)2的理论研究

用INDO系列方法对自由基C59N及双体(C59N)2进行了理论研究,结果表明: N的掺入使C60笼发生畸变, N向笼外突出, 碳氮6-6键上的C自旋密度较大, 两C59N自由基在这个碳上以C-C单键连接形成双体为C2h, C2v对称性。其中C2v构型更稳定, 且N与附近的三个碳均以单键连接。理论计算的电子光谱与实验吻合较好。(C59N)2易分解为单体C59N。     

C_(70)PH可能异构体的结构与稳定性的理论研究

分别用半经验的AM1, PM3及MNDO方法研究了富勒烯衍生物C_(70)PH的12种可能异构体的结构和稳定性。计算结果表明: -PH基团加成在4种6-6键上的稳定构型中,非赤道带6-6键加成的三个异构体为闭环结构,赤道带6-6键加成的一个异构体为开环结构;-PH基团加成在4种6-5键上均可产生开环和闭环2种稳定构型。加成在6-5双键的异构体其闭环构型更稳定,加成在6-5单键的异构体其开环构型更稳定。闭环异构体中-PH基团加成在碳球极处6-6键上的构型1,2最稳定,开环异构体中-PH基团加成在赤道带6-6键上的构型8最稳定。     

Structure and stability of the defect fullerene clusters of C60: C59, C58, and C57

We have performed density functional calculations for the structures and stabilities of various isomers of the defect fullerene clusters of C(60): C(59), C(58), and C(57). The C(59_)5-8, C(58_)5-5-7, and C(57_)4-5-9 clusters were calculated to be the most stable isomers of the C(59), C(58), and C(57) clusters, respectively. There are obvious relationships between structure and stability of the defect fullerene clusters. First, an unsaturated carbon atom favors being located at a 6-membered ring rather than a 5-membered ring. Second, the most stable isomers prefer to have newly formed 5-membered rings, rather than newly formed 4-membered rings.     

(MN)nHm(M=Ga,In; n=1-4; m=1, 2)团簇的结构与稳定性

采用密度泛函理论(DFT)的B3LYP方法, 在6-31G**和Lanl2dz水平上分别对(MN)nHm(M=Ga, In; n=1-4; m=1, 2)进行了优化和振动频率计算. 得到了上述团簇的最稳定构型、H原子的结合能以及它们的能隙. 结果表明, (MN)nH(M=Ga, In; n=1-4)的基态构型均为双重态, (MN)nH2(M=Ga, In; n=1-4)的基态构型均为单重态; 当氢的个数为1时, 加在N原子上比加在M(M=Ga, In)原子上稳定, 如有N3单元, 那么加在N3单元两侧的构型是相同的, 且它是最稳定的; 当氢的个数为2时, 除n=1外, 分别加在两个N原子上的构型是最稳定的, 如有N3单元, 那么分别加在N3单元分离最远的两个N原子的构型是最稳定的. GaNH、(GaN)3H 和InNH的结合能和能隙都很大, 说明这些团簇都有很高的稳定性.     

异质富勒烯C58BN的结构与光谱研究

用AM1、MNDO和INDO半经验方法研究了异质富勒烯C₅₈BN各异构体的结构、稳定性和电子光谱.所有这些半经验方法给出了相似的稳定性顺序.结果表明,在6-6位置取代的异构体是最稳定的,异构体的稳定性随杂原子间距离的增加而降低;与C₆₀相比,硼氮杂富勒烯C₅₈BN具有较低的前线轨道能级差、较小的电离势和较低的稳定化能.C₅₈BN很可能具有与C₆₀分子相似的反应活性,易发生亲核反应,但比C₆₀更易失去电子形成正离子.以AM₁优化构型为基础,利用INDO/CIS方法计算了各异构体的电子光谱.     

Ab initio study of the structures and stabilities of the dimer of ethyl cation, (C(2)H(+)(5))(2) and related C(4)H(10)(2+) isomers.

Ab initio calculations at the MP4(SDTQ)/6-311G//MP2/6-31G level were performed to study the structures and stabilities of the dimer of ethyl cation, (C(2)H(+)(5))(2), and related C(4)H(10)(2+) isomers. Two doubly hydrogen bridged diborane type trans 1 and cis 2 isomers were located as minima. The trans isomer was found to be more favorable than cis isomer by only 0.6 kcal/mol. Several other minima for C(4)H(10)(2+) were also located. However, the global energy minimum corresponds to C-H (C(4) position) protonated 2-butyl cation 10. Structure 10 was computed to be substantially more stable than 1 by 31.7 kcal/mol. The structure 10 was found to be lower in energy than 2-butyl cation 13 by 34.4 kcal/mol.     

On the structure and relative stability of C50 fullerenes

The complete set of 271 classical fullerene isomers of C50 has been studied by full geometry optimizations at the SAM1, PM3, AM1, and MNDO quantum-chemical levels, and their lower energy structures have also been partially computed at the ab initio levels of theory. A D(5h) species, with the least number of pentagon adjacency, is predicted by all semiempirical methods and the HF/4-31G calculations as the lowest energy structure, but the B3LYP/6-31G* geometry optimizations favor a D3 structure (with the largest HOMO-LUMO gap and the second least number of adjacent pentagons) energetically lower (-2 kcal/mol) than the D(5h) isomer. To clarify the relative stabilities at elevated temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the HF/4-31G level for the first time. The computed relative-stability interchanges show that the D3 isomer behaves more thermodynamically stable than the D(5h) species within a wide temperature interval related to fullerene formation. According to a newly reported experimental observation, the structural/energetic properties and relative stabilities of both critical isomers (D(5h) and D3) are analyzed along with the experimentally identified decachlorofullerene C50Cl10 of D(5h) symmetry. Some features of higher symmetry C50 nanotube-type isomers are also discussed.     

Theoretical investigation of C56 fullerene isomers and related compounds

All the 924 classical isomers of fullerene C(56) have been investigated by PM3, and some most stable isomers are refined with HCTH/3-21G and B3LYP6-31G(d) methods. D(2):003 with the least number of adjacent pentagons is predicted to be the most stable isomer at B3LYP/6-31G(d) level, while C(s):022 and C(2):049 possess nearly degenerate energies with relative energies of 0.03 and 3.90 kcal/mol, respectively. However, as to dianionic C(56)(2-) fullerene, C(2v):011 is predicted to be the most stable isomer. Investigations also show that the encapsulation of Ca atom in C(56) fullerene is exothermic and the metallofullerenes Ca@C(56) can be described as Ca(2+)@C(56)(2-). The computed relative stabilities show that the D(2):003 behaves more thermodynamically stable than other isomers in a wide temperature interval, and C(2v):011 should also be an important component. The electronic isomerization of C(56) (C(2v):011) and C(50) (D(5h):002) indicates that this phenomenon might be rather general in fullerenes and causes different properties, thus bringing about new possible applications of fullerenes. The static second-order hyperpolarizabilities of the three most stable isomers are slightly larger than that of C(60).     

Proton Migration in Benzene Complexes of Methyl and Silyl Cations

Quantum-chemical calculations at the B3LYP/6-31G(d,p) level of theory were used to optimize stationary points in the C₆H₆ + H₃X⁺ (X = C, Si) systems. At X = Si, the adduct of the cation with benzene is the most stable isomer, whereas at X = C, the para isomer is more stable than the adduct (ipso isomer). This difference is explained in terms of charge distribution in the benzene ring in toluene and phenylsilane: In the latter, the negative charge on the carbon atom attached to silicon is much higher than on the other carbon atoms, unlike toluene in which the highest negative charge is on the carbon atom para to the methyl group. Proton migration from the ipso to para position requires the lowest (X = C) and highest (X = Si) barriers to be overcome compared with the other barriers to proton migration over the benzene ring. These barriers and relative stabilities of the isomers correlate well with the charge distribution on benzene carbon atoms in toluene and phenylsilane.     

N5H5异构体的结构与稳定性的理论研究

采用密度泛函理论的B3LYP方法在6-311++G**基组水平上对N5H5氮氢化合物异构体可能存在的构型进行了几何优化, 得到23种稳定异构体, 并研究了这些异构体间可能的互变异构情况. 为了讨论N5H5异构体作为含能材料候选物质的可能性, 还采用了G3B3方法计算了能量, 并且计算了异构体的生成热(⊿Hf,298).结果表明, 在23种异构体中链状异构体最稳定, 四元环四氮烷异构体最不稳定, 存在一个N=N双键的异构体较同类异构体能量低, 较为稳定; N5H5氮氢化合物的生成热均为正, 其中异构体E1生成热最高. 估算了N5H5的摩尔体积, 由密度公式ρ=MT/Vmol,得到E1 的密度最大.