C59XH（X=N,B）与1,3-丁二烯Diels-Alder环加成反应的区域选择性

应用半经验的AMI和密度泛函B3LYP/6-31G*方法对1,3-丁二烯与C59XH(X=N,B)Diels-Alder环加成反应的区域选择性进行理论研究,选择一些有代表性的C59XH(X=N,B)的6-16键探讨环加成反应的机理.1,3-丁二烯与C59NH进行的Diels-Alder反应,随着加成位置远离C59NH的N原子,活化能越来越低,但都比1,3-丁二烯与C60相应反应的活化能高.与此相反,对于1,3-丁二烯与C59BH进行的环加成反应.加成位置最靠近B原子的2,12/r-和2,12/f-过渡态的势垒最低,并且比1,3-丁二烯与C60进行环加成反应的活化能约低18 kJ·mol-1,其产物也是热力学最稳定的.与C60相应的反应相比,C59NH和C59BH中N和B原子不同的电子性质对其邻位双键进行Diels-Alder环加成反应的活性产生了不同影响,前者使反应活性降低,后者使反应活性增强.     

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．     

C60富勒烯-哌啶硫代荒酸酯稠合体的合成与三线态特征

C₆₀富勒烯与2-(哌啶-硫代荒酸酯)-1,3-丁二烯通过Diels-Alder环加成反应得到C₆₀富勒烯-哌啶硫代荒酸酯稠合体,运用现代波谱技术等确定了产物结构;用半经验方法PM3和AM1计算预测环加成反应性和C₆₀富勒烯-哌啶硫代荒酸酯稠合体的性能.激光光解时间分辨技术初步探究了单加成的C₆₀富勒烯-哌啶硫代荒酸酯稠合体(C₆₀-PX)三线态特征以及与四-(2-噻吩基)-四硫富瓦烯(TT-TTF)分子间的光诱导电子转移反应.     

2,5-二甲基噻吩硫氧化物与C60的Diels-Alder反应研究

通过2,5-二甲基噻吩硫单氧化物(亚砜)和2,5-二甲基噻吩硫二氧化物(砜)与C60的Diels-Alder环加成反应,分离获得了稳定加成产物。     

现行高中化学课本有机化学部分几个值得商榷的问题

关于1,3-丁二烯的亲电加成反应 1,3-丁二烯跟卤素、卤化氢等试剂容易发生亲电加成反应。当它跟一分子卤素或一分子卤化氢等发生亲电加成时,一般既可得到1,4-加成产物,也可得到1,2-加成产物,而两种产物的比例,则取决于反应温度、试剂和溶剂的性质、产物的稳定性等诸因素。     

C_(60)与N-羧甲基脱氢枞胺的1,3-偶极环加成反应研究

以脱氢枞胺的衍生物N-羧甲基脱氰枞胺与C60及多聚甲醛为原料,于N2保护下在甲苯中回流48h,经1,3-偶极环加成反应,得到脱氢枞胺基团加成度不同的三种C60吡咯烷衍生物,并对它们的结构进行了表征.     

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.     

炔烃与[Cp*Ru(H2O)(NBD)]BF4的[2+2+2]Diels-Alder反应

过渡金属催化的[2 2 2]环加成反应由于没有原子损失和较高的立体选择性,在合成不饱和多环化合物中已经被广泛应用[1].但一般反应时间较长,反应时常需要加热.我们发现金属有机化合物[Cp*Ru(H2O)(NBD)]BF4(Cp*是五甲基环戊二烯基,NBD是降冰片二烯)中的NBD与甲基苯基乙炔在室温就可发生[2 2 2]Diels-Alder反应[2].进一步研究发现,在室温下,炔烃PhC三CR(R=H,COOEt,Ph)和双炔烃HC三CC6H4C6H4C三CH与[Cp*Ru(H2O)-(NBD)]BF4中的NBD也能进行Diels-Alder反应,30 min即以较高产率生成[2 2 2]环加成产物.     

氯化锌催化下C60与枞酸的反应

拟利用枞酸分子中的非同环共轭二烯在氯化锌作用下异构化成具有同环共轭二烯的海松酸结构, 再与C₆₀进行Diels-Alder加成反应, 预测可以得到Diels-Alder加成产物. C₆₀、枞酸及氯化锌在邻二氯苯溶剂中, 在氮气保护下于175～180 ℃反应8 h, 将反应物洗涤后进行硅胶柱层析分离, 采用FT-IR, ¹³C NMR, ¹H NMR和MALDI-TOF-MS等分析方法对反应主要产物进行结构测定, 却意外发现得到C₆₀与枞酸的加成过程中发生了脱羧脱氢反应且产物含有芳环的化学结构.     

[60]富勒烯与1,1′-联茚的Diels-Alder加成物的合成与结构表征

通过Diels-Alder环加成反应,发现可控制反应条件,使1,1′-联茚与C60反应,并高产率地得到具有新颖结构的单加成物.用HPLC,FT-IR,FD-MS及1H NMR,13C NMR,HMQC,HMBC等多种波谱技术对其结构进行表征,测得它的两个sp3杂化的桥头碳的化学位移为δC:70.91,证明生成的衍生物为[6,6]闭式环加成.13C NMR谱共给出38个信号,表明C601,1′-联茚衍生物分子具有Cs对称性;此外,还发现单加成衍生物C601,1′-联茚热稳定性好,在四氢呋喃、丙酮等极性溶剂中溶解性好,很适合于在LB膜及光限幅性能方面的研究.     

Regioselectivity of 1,3-Butadiene Diels-Alder Cycloaddition to C59XH (X=N, B)

The regioselectivity of Diels-Alder cycloaddition of 1,3-butadiene to C₅₉XH (X=N, B) has been studied theoretically by means of the semiempirical AM1 and DFT (B3LYP/6-31G^*) methods. The mechanisms of the cycloaddition on some selected 6.6 bonds of C₅₉XH (X=N, B) have been analyzed. For C₅₉NH, the activation energies become lower with the addition site increasingly farther from the N atom; however, they are all higher than that of the reaction of 1,3-butadiene with C₆₀. In contrast to C59NH, for the cycloaddition to C₅₉BH, the activation energies corresponding to 2,12/r- and 2,12/f-transition states, in which the addition sites are the nearest ones to the B atom, are the lowest ones, and are lower than that of the reaction of 1,3-butadiene with C₆₀ by over 18 kJ·mol⁻¹, and the products corresponding to these two transition states are the most stable ones. The different electronic natures of N and B atoms results in different effects on the Diels-Alder reactions of 1,3-butadiene with C₅₉NH and C₅₉BH; the former makes the reactivity of C₅₉NH reduced and the latter makes the reactivity of C₅₉BH enhanced, relative to that of C₆₀.     

Dispersion corrections essential for the study of chemical reactivity in fullerenes

In a previous paper (J. Phys. Chem. A2009, 113, 9721), we analyzed theoretically the Diels-Alder cycloaddition between cyclopentadiene and C(60) for which experimental results on energy barriers and reaction energies are known. One of the main conclusions reached was that the two-layered ONIOM2(B3LYP/6-31G(d):SVWN/STO-3G) method provides results very close to the full B3LYP/6-31G(d) ones. Unfortunately, however, both the exothermicity of the reaction and the energy barrier were clearly overestimated by these two methods. In the present work, we analyze the effect of the inclusion of Grimme's dispersion corrections in the energy profile of this reaction. Our results show that these corrections are essential to get results close to the experimental values. In addition, we have performed calculations both with and without dispersion corrections for the Diels-Alder reaction of C(60) and several dienes and for the Diels-Alder cycloaddition of a (5,5) single-walled carbon nanotube and 1,3-cis-butadiene. The results obtained indicate that inclusion of dispersion corrections is compulsory for the study of the chemical reactivity of fullerenes and nanotubes.     

Sigma- and pi-bond strengths in main group 3-5 compounds

The sigma- and pi-bond strengths for the molecules BH2NH2, BH2PH2, AlH2NH2, and AlH2PH2 have been calculated by using ab initio molecular electronic structure theory at the CCSD(T)/CBS level. The adiabatic pi-bond energy is defined as the rotation barrier between the equilibrium ground-state configuration and the C(s)symmetry transition state for torsion about the A-X bond. We also report intrinsic pi-bond energies corresponding to the adiabatic rotation barrier corrected for the inversion barrier at N or P. The adiabatic sigma-bond energy is defined as the dissociation energy of AH2XH2 to AH2 + XH2 in their ground states minus the adiabatic pi-bond energy. The adiabatic sigma-bond strengths for the molecules BH2NH2, BH2PH2, AlH2NH2, and AlH2PH2 are 109.8, 98.8, 77.6, and 68.3 kcal/mol, respectively, and the corresponding adiabatic pi-bond strengths are 29.9, 10.5, 9.2, and 2.7 kcal/mol, respectively.     

Organic functionalization of the sidewalls of carbon nanotubes by diels-alder reactions: a theoretical prediction

[structure: see text] The viability of the Diels-Alder (DA) cycloaddition of conjugated dienes onto the sidewalls of single-wall carbon nanotubes is assessed by means of a two-layered ONIOM(B3LYP/6-31G:AM1) approach. Whereas the DA reaction of 1,3-butadiene on the sidewall of an armchair (5,5) nanotube is found to be unfavorable, the cycloaddition of quinodimethane is predicted to be viable due to the aromaticity stabilization at the corresponding transition states and products.     

PAH formation under single collision conditions: reaction of phenyl radical and 1,3-butadiene to form 1,4-dihydronaphthalene

The crossed beam reactions of the phenyl radical (C(6)H(5), X(2)A(1)) with 1,3-butadiene (C(4)H(6), X(1)A(g)) and D6-1,3-butadiene (C(4)D(6), X(1)A(g)) as well as of the D5-phenyl radical (C(6)D(5), X(2)A(1)) with 2,3-D2-1,3-butadiene and 1,1,4,4-D4-1,3-butadiene were carried out under single collision conditions at collision energies of about 55 kJ mol(-1). Experimentally, the bicyclic 1,4-dihydronaphthalene molecule was identified as a major product of this reaction (58 ± 15%) with the 1-phenyl-1,3-butadiene contributing 34 ± 10%. The reaction is initiated by a barrierless addition of the phenyl radical to the terminal carbon atom of the 1,3-butadiene (C1/C4) to form a bound intermediate; the latter underwent hydrogen elimination from the terminal CH(2) group of the 1,3-butadiene molecule leading to 1-phenyl-trans-1,3-butadiene through a submerged barrier. The dominant product, 1,4-dihydronaphthalene, is formed via an isomerization of the adduct by ring closure and emission of the hydrogen atom from the phenyl moiety at the bridging carbon atom through a tight exit transition state located about 31 kJ mol(-1) above the separated products. The hydrogen atom was found to leave the decomposing complex almost parallel to the total angular momentum vector and perpendicularly to the rotation plane of the decomposing intermediate. The defacto barrierless formation of the 1,4-dihydronaphthalene molecule involving a single collision between a phenyl radical and 1,3-butadiene represents an important step in the formation of polycyclic aromatic hydrocarbons (PAHs) and their partially hydrogenated counterparts in combustion and interstellar chemistry.     

Diels-Alder Reaction of phosphaethene with 1,3-dienes: an ab initio study

Computations on Diels-Alder (DA) reactions of phosphaethene with 1,3-butadiene and with isoprene reveal asynchronous transition structures. The DFT (B3LYP/6-311+G) activation energies of these reactions, 12-14 kcal/mol, are much lower than that of the parent ethene-butadiene reaction, 28 kcal/mol, even though the exothermicities of all lie in the same range, from -29 to -33 kcal/mol. The transition states (TSs) for the phosphethene-butadiene or isoprene DA reactions are earlier than the TSs of the butadiene-ethene cycloaddition. Due to the weakness of the C=P pi bond compared to the C=C pi bonds, the energies required to reach the phosphaethene TSs are much less than the carbocyclic cases. The computed (1)H NMR chemical shifts and nucleus independent chemical shifts (NICS) quantify the aromatic character of the transition states. Regioselectivities of the neutral phosphaethene-isoprene DA reactions are modest, at best. However, computations on radical cation DA reactions of phosphaethene with isoprene, which proceed stepwise with open chain intermediates, can account for the high regioselectivities that have been observed in some cases.     

Theoretical study on the regioselectivity of the B80 buckyball in electrophilic and nucleophilic reactions using DFT-based reactivity indices

Density functional theory calculations at the B3LYP/SVP and B3LYP/6-311G(d) levels were carried out for a series of XH(3)B(80) complexes with X = {N, P, As, B, Al}. To probe the regioselectivity of B(80), the electronic Fukui function, the molecular electrostatic potential (MEP), and the natural bond orbital (NBO) were determined. These indices were shown to provide reliable guides to predict the relative reactivities of the boron buckyball sites. Thermodynamic stabilities of the complexes formed by the reaction of B(80) with nucleophiles (NH(3), PH(3), AsH(3)) and electrophiles (BH(3), AlH(3)) are in good agreement with the prediction of regioselectivity indicated on the basis of Fukui and MEP indices. The qualitative results suggest the boron buckyball to be an amphoteric and hard molecule. It has two distinct reactive sites localized on caps and frame, which act as acids and bases, respectively. Most of the complexes are stable with formation energies comparable to that of the analogous complexes of the borane molecule, BH(3)BH(3), BH(3)NH(3), and BH(3)AlH(3). The B-H-B bond characteristics of diborane are recovered in B(80)BH(3). Exohedral complexes are more stable than endohedral complexes. The most stable complexes are those with NH(3) on the caps and BH(3) on the pentagonal ring of B(80).     

Diverse Reactivity of Dienes with Pentaphenylborole and 1-Phenyl-2,3,4,5-Tetramethylborole Dimer

The reactions of a monomeric borole and a dimeric borole with 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene were investigated. The monomeric borole reacted at ambient temperature whereas heat was required to crack the dimer to form the monomer and induce reactivity. 2,3-Dimethyl-1,3-butadiene reacts to give diverse products resulting from a cycloaddition process with the B−C moiety of the boroles acting as a dienophile, followed by rearrangements to furnish bicyclic species. For 1,3-cyclohexadiene, a [4+2] process is observed in which 1,3-cyclohexadiene serves as the dienophile and the boroles as the diene partner. The experimental results are corroborated with mechanistic theoretical calculations that indicate boroles can serve as either a diene or dienophile in cycloaddition reactions with dienes.     

Conformational selectivity in the diels-alder cycloaddition: predictions for reactions of s-trans-1,3-butadiene

Diels-Alder cycloaddition of s-trans-1,3-butadiene (1) should yield trans-cyclohexene (7), just as reaction of the s-cis conformer gives cis-cyclohexene (9). Investigation of this long-overlooked process with Hartree-Fock, Moller-Plesset, CASSCF, and DFT methods yielded in every case a C(2)-symmetric concerted transition state. At the B3LYP/6-31G (+ZPVE) level, this structure is predicted to be 42.6 kcal/mol above reactants, while the overall reaction is endothermic by 16.7 kcal/mol. A stepwise diradical process has been studied by UBLYP/6-31G theory and found to have barriers of 35.5 and 17.7 kcal/mol for the two steps. Spin correction lowers these values to 30.1 and 13.0 kcal/mol. The barrier to pi-bond rotation in cis-cyclohexene (9) is predicted (B3LYP theory) to be 62.4 kcal/mol, with trans-cyclohexene (7) lying 53.3 kcal/mol above cis isomer 9. Results suggest that pi-bond isomerization and concerted reaction may provide competitive routes for Diels-Alder cycloreversion. It is concluded that full understanding of the Diels-Alder reaction requires consideration of both conformers of 1,3-butadiene.