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．     

Sm金属富勒烯的高效提取和电化学性质研究

在金属富勒烯 [1]的形成过程中 ,存在从金属到碳笼的电子转移 .La系金属富勒烯中 ,金属原子转移 2或 3个电子给碳笼形成 + 2或 + 3价的金属离子和带有大量负电荷的碳笼 .尽管如此 ,金属富勒烯仍具有良好的接受电子的能力 [2 ,3] .大多数的 La系金属富勒烯 ( Y,La,Ce,Pr,Nd,Gd,Tb,Dy,Ho,Er,L u)的电化学方法研究表明 ,它们可以接受 5到 6个电子 ,但是 ,Sm的金属富勒烯的氧化还原性质尚未见报道 ,其主要原因是 Sm金属富勒烯的合成产率低 ,仅是 La金属富勒烯的 7% ,从而使得其分离非常困难 ,需要通过多步 HPLC循环才能得到 [4 ,5] ,高…     

C59H3N异构体的结构与稳定性的理论研究

分别用MNDO,AM1和PM3三种半经验方法对C59HN所有1-2,1-4和1-6氢加成物C59H3N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氢加成物的立体选择性规律与C60和C60H2的不同,最稳定异构体不是1-2加成物,而是1-4加成的6,18-或12,15-异构体,次稳定异构体为1-2加成物,三种半经验方法计算得到的两者能量差为13～15kJ/mol,N原子取代碳笼骨架C原子后,改变了碳笼氢加成物的立体选择性规律.     

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。     

苯二酚异构体双电荷离子和单电荷离子的动能谱研究

本文利用质量分析离子动能谱(MIKES)、碰撞诱导解离(CID)技术和电子捕获诱导解离(ECID)技术, 研究了邻、间、对苯二酚分子在电子轰击质谱(EIMS)中产生的双电荷离子[C6H6O2]^2^+, [C6H4O]^2^+和单电荷离子[C6H6O2]^+。根据测定的电荷分离反应动能释放值T和由此计算出的两电荷间距R, 推测出过渡态的结构。有趣的是, 可利用单电荷离子[C6H6O2]^+的MIKES/CID谱区分苯二酚异构体。     

异质富勒烯C58P2的理论研究

用ＭＮＤＯ半径能方法研究了异质富勒烯Ｃ５８Ｐ２各异构体的结构和相对稳定性。结果表明,１,４－位取代的异构体最稳定,异构体的稳定性随杂原子同距离的增加而降低。Ｃ５５８Ｐ２分子和稳定性比全碳富勒烯Ｃ６０低,但仍具有相当的稳定性,是潜在的合成目标。杂原子磷的掺杂改善了富勒烯的氧化还原性能。考察了各异构体的整体硬度和绝对电负性,产根据绝对电负性的差异预测了富勒烯和异质富勒烯间形成聚合物时的电子转移。     

富勒烯C_(36)等电子体C_(34)BN异构体的结构及其相对稳定性理论研究

用半经验的AM1和MNDO方法优化了富勒烯C_(36)的等电子体C_(34)BN所有可能 异构体的构型,分析了各异构体相对稳定性与杂原子取代位置间的关系。另外,比 较了C_(36)碳笼上同位置地取代杂原子形成的C_34BN,C_(34)B_2和C_(34)N_2间的 电子结构,并分析了C_(34)BN最稳定异构体的振动模型。结果表明以C_(36):A (D_(6h))为母体形成的最稳定C_(34)BN异构体对应于碳笼赤道位置六元环中1,4- 取代产物,而以C_(36):B(D_(2d))为母体形成的最稳定C_(34)BN异构体对应于碳笼 近赤道位置的1,2-取代产物.C_(34)BN各异构体的稳定性可能主要由体系的共轭性 质决定。前线轨道能级表明B,N原子取代所得异构体的氧化-还原活性按以下顺序 递增：C_(34)B_2相似文献   

二甲苯异构体双电荷离子和单电荷离子的动能谱研究

利用质量分析离子动能谱和碰撞诱导解离技采研究了邻、间、对二甲苯分子在电子轰击质谱中产生的双电荷离子[C8H10]2+、[C8H9]2+和单电荷离子[C8H10]+。根据测定的电荷分离反应的释放动能T和由此估算的双电荷离子电荷分离反应过渡态两电荷间距R,推测出过渡态的结构,利用单电荷离子[C8H10]+的MIKES/CID谱可区分邻二甲苯与间、对二甲苯异构体.     

骨架掺硼富勒烯的合成及表征

在富勒佛被合成后不久，Smalley等人就开始利用B、N、St等元素制备非碳富勒烯和骨架掺杂富勒烯的研究，合成出了骨架掺氮富勒佛一C59N，在质谱中观察到了微观量的骨架接棚富勒烯C。。B等［’－’］，但迄今尚未见非碳富勒烯和骨架掺棚富勒烯宏观是合成的报导．用础部分取代富勒     

DBU及DBN与丙炔酸甲酯的迈克尔型加成及其产物的核磁共振谱学研究

1,8-二氮杂二环[5,4,0]十一碳-7-烯(DBU及1,5-二氮杂二环[4,3,0]壬碳-5-烯与丙炔酸甲酯反应可生成成环化合物。通过对成环产物的^1H NMR、^1H-^1H COSY、^13C NMR谱的分析,讨论了其化学位移及J-偶合特征。同时研究了整个反应可能的历程和机理。     

C77N+异构体的稳定性和电子光谱研究

All of the possible 21 isomers for C77N+, an isoelectronic molecule of C78, were investigated by the INDO methods based on C78(C2V). It indicates from optimization that the most stable isomer is that the nitrogen atom substitutes C(78) located at the C(78)-C(73) bond passed through by the Y shortest axis and the atoms near the Z longest axis are also easy to substitute, whereas the atoms near the X shortest axis are relatively difficult to substitute. At the same time, C78 was compressed a little and ready to perform the further reaction to form C77 NR at the location of substitution. Electronic spectra of C77N+ were calculated by INDO/SCI method and electronic transition was theoretically assigned. The red shift of absorption peaks for electronic spectra of C77N+ took place compared with that of C78(C2V) because of its narrower LUMO HOMO energy gap. There are great differences in characteristic absorptions among C77N+ isomers, which can be considered as evidence of the formation for each isomer.     

Crystal structures of the NO and N2O4 sorption complexes of fully dehydrated fully Cd2+-exchanged zeolite X (FAU): coordination of neutral NO and N2O4 to Cd2+

The structures of the nitric oxide and dinitrogen tetroxide sorption complexes of dehydrated fully Cd2+-exchanged zeolite X (FAU) have been determined using single-crystal X-ray diffraction in the cubic space group Fdm at 21(1) degrees C. Ion exchange was accomplished by allowing an aqueous stream 0.05 M in Cd2+ to flow past each crystal for 5 days. Each crystal was then dehydrated at 500 degrees C and 2 x 10(-6) Torr for 2 days, followed by exposure to 100 Torr of zeolitically dry NO or NO2/N2O4 gas. The structures were determined in these atmospheres. The unit cell constants at 21(1) degrees C are 24.877(2) A for the dark-yellow NO complex, |Cd46(NO)16|[Si100Al92O384]-FAU, and 24.735(2) A for the black N2O4 complex, |Cd46(N2O4)25.5|[Si100Al92O384]-FAU. The structure of the NO complex was refined to R1 = 0.072 and wR2 = 0.134. In this structure, Cd2+ ions occupy four crystallographic sites. Fifteen Cd2+ ions occupy site I (at the centers of the double 6-rings (D6Rs)), and one occupies site I' (in the sodalite cavity opposite a D6R). The remaining 30 Cd2+ ions occupy two different sites II (near 6-rings in the supercages): 16 coordinate to nitric oxide molecules and 14 do not. Sixteen NO molecules lie in the supercage where each interacts weakly with a Cd2+ ion: Cd-N = 2.57(22) A. The observed N-O bond distance is 1.28(25) A and Cd-N-O is 118(10) degrees. The structure of the N2O4 complex was refined to R1 = 0.084 and wR2 = 0.216. In this structure, Cd2+ ions occupy only three crystallographic sites. The 16 D6Rs per unit cell are filled with 11.5 Cd2+ ions at site I and 9 Cd2+ ions at site I': 11.5 + 9/2 = 16. The remaining 25.5 Cd2+ ions occupy site II where each coordinates at 2.43(8) A to a nitrogen atom of a N2O4 molecule. At the coordinating nitrogen atom, O-N-O is 147(10) degrees and the N-O bond lengths are 1.07(9) and 1.23(10) A. At the second nitrogen atom, O-N-O is 140(10) degrees, and the N-O bond lengths are 1.03(13) and 1.42(12) A. The imprecisely determined N-N bond length, 2.74(17) A, appears to be very much lengthened by coordination to Cd2+. The Cd-N-N angle is 144(10) degrees. This appears to be the first crystallographic report of the coordination of N2O4 to a cation.     

1H, 13C and 15N NMR studies on adducts formation of rhodium(II) tetraacylates with some azoles in CDCl3 solution

Adduct formations of rhodium(II) tetraacetate and tetratrifluoroacetate with some 1H-imidazoles, oxazoles, thiazoles, 1H-pyrazoles and isoxazole have been investigated by the use of 1H, 13C, 15N NMR and electronic absorption spectroscopy (VIS) in the visible range. Azoles tend to form axial adducts containing rhodium(II) tetraacylates bonded via nitrogen atom. Bulky substituents close to the nitrogen atom prevent the Rh--N bond formation, and in several cases switch over the binding site to the oxygen or sulphur atoms. The (15)N adduct formation shift Deltadelta(15N) (Deltadelta = delta(adduct) - delta(ligand)) varied from ca - 40 to - 70 ppm for the nitrogen atom involved in complexation, and of a few parts per million only, from ca - 6 to 3 ppm, for the non-bonded nitrogen atom within the same molecule. The Deltadelta(1H) values do not exceed one ppm; Deltadelta(13C) ranges from - 1 to 6 ppm. Various complexation modes have been proved by electronic absorption spectroscopy in the visible region (VIS). For comparison purposes, some adducts of pyridine, thiophene and furan derivatives have been measured as well. The experimental findings were compared with calculated chemical shifts, obtained by means of DFT B3LYP method, using 6-311 + G(2d,p), 6-31(d)/LanL2DZ and 6-311G(d,p) basis set.     

Halogen Bonds in Adenine-5-Bromouracil Complexes

Ab initio and density functional calculations were employed to investigate the bonding patterns in theadenine-5-bromouracil (AT+) complexes. It is shown that the Br atom in 5-bromouracil (T+) is involved in bonding both with the hydrogen atom of the amino group of adenine (A) and with N7(A) (or N1(A)). With this motif, the Br atom interacts with a nucleophile (H) in a "head-on" fashion and an electrophile(N) in a "side-on" fashion, forming both hydrogen and halogen bonds. Electrostatic attraction between the Br atom in T+ and N7 (or N1) of adenine was found via the electrostatic potential analysis. The existence of the Br···N interactions in the pairs was further conˉrmed by means of Bader's atoms in molecules theory. A bond critical point is identiˉed for the halogen bonds and the topological parameters at the bond critical point indicate the typical closed-shell interactions in the pairs. Natural bond orbital analysis suggests that the charge transfer from the lone pair of the nitrogen atom of adenine is mainly directed to the C-Br antibonding orbital. Finally, halogen bonds in the T+AT+A tetrads were also explored.     

胞嘧啶…NO复合物结构与性质的理论研究

用密度泛函理论在BL3YP/6-311＋G*基组水平上对胞嘧啶…NO复合物体系进行了理论计算, 发现了6个能量极小的复合物. 其结合方式是NO的N或O原子与胞嘧啶的N—H键形成氢键, 最稳定的复合物的结合能为－9.65 kJ/mol. NO的N原子与胞嘧啶的结合具有更强的优势, N结合的复合物中NO的键长缩短, 而O结合的复合物中NO键长伸长. 同时, 对复合物的振动分析发现, 在胞嘧啶中所有的与NO结合的N—H键的伸缩频率下降, 而所有氨基的面内弯曲振动频率是增加的.     

胞嘧啶与一氧化碳复合物的结构与性质

在B3LYP/6-311+G**水平上对胞嘧啶…CO复合物体系进行了理论计算, 发现了6个能量极小的复合物. 其结合方式是CO的C或O原子与胞嘧啶的N—H键形成氢键, 最稳定的复合物的结合能为-8.72 kJ·mol-1. CO的C原子与胞嘧啶的结合具有更强的优势, C原子结合的复合物中CO的键长缩短, 而O结合的复合物中CO键长伸长. 同时, 对复合物的振动分析发现, 在C原子结合的复合物中CO的伸缩频率蓝移, 而O结合的复合物中CO伸缩频率是红移的.     

Bond Energy Scheme for Estimating Heats of Formation of Monomers and Polymers. VII. Nitrogen Compounds

The bond energy scheme is extended to nitrogen compounds by correlating experimental thermochemical data reviewed to 1980. Heats of formation and atomization energy terms are provided for bonds of nitrogen with other elements: H, C, O, N, S, and halogens. An overall precision of 3 kcal/mol was attainable at the best, which is rather low for chemical reaction kinetics purpose. This is attributable mainly to the intrinsically unpredictable bond energies of the nitrogen atom due to the “lone-pair” electrons participation in the valence bonding, rendering nitrogen bonds specific and less transferable. The nearest-neighbor interactions on nitrogen atom are also severe but predictable if sufficient energy terms are generated. The concept of ring strain in five-membered rings (about 5 × 2 kcal/mol in the background of thermochemical data) has been reviewed and amended by providing a special set of energy terms for the (C, O, N, S) -ring skeleton which is considered strain-free if the hydrogen atom is the only substituent. Heats of formation of some common molecular structures are predicted.

Heats of formation of nitrogen-containing polymers and heats of polymer-forming and polymer-modification reactions are estimated and compared with available calorimetric data.     

1-Fluoro-2-hydrostibatrane

1-Fluoro-2-hydrostibatrane was synthesized by the reaction of antimony trifluoride with triethanolamine. The molecular structure of the compound was studied by X-ray diffraction and multinuclear magnetic resonance. The coordination polyhedron of the Sb atom is intermediate between a distorted tetrahedron (AX₄E type of molecule) and a tetrahedral pyramid (AX₄DE type of molecule). Diastereotopism of the geminal protons of each methylene group in the half-rings of the heterocycle, observed in the NMR spectra, vanishes at 65°C because of reversible cleavage of the N → Sb coordination bond and inversion of the nitrogen atom. The chemical environment of the OCH₂ and NCH₂ protons of the heterocycle and 2-hydroxyethyl protons is averaged due to the fast prototropic tautomerism at 75–120°C (in DMSO-d ₆).     

Modeling a central ligand in the nitrogenase FeMo cofactor

In very recent work by Einsle et al. (Science 2002, 297, 1696), a new X-ray crystallographic structure of the FeMo cofactor of nitrogenase with a central ligand was presented. The central ligand is a light atom (N, O, or C), and Einsle et al. suggest that it is nitrogen. We present density functional calculations on the FeMo cofactor, and we investigate N, O, and C as central ligands. We show that both N and O lead to energetically stable FeMo cofactor structures, whereas C is energetically unfavorable. By comparison of bond geometries with the crystallographically determined values, we show that the central ligand is most likely nitrogen.     

A computational study of the reaction of ground-state nitrogen atoms with chloromethyl radicals

A computational study of the N(4S) + CH2Cl reaction has been carried out. The first step of the reaction is the formation of an initial intermediate (NCH2Cl), which is relatively stable and does not involve any energy barrier. The two most exothermic products are those resulting from the release of a chlorine atom, H2C=N + Cl and trans-HC=NH + Cl. A kinetic study within the framework of the statistical theories suggests that the kinetically preferred product is also the most exothermic one. This is in contrast with the analogue reaction of nitrogen atoms with CH2F, where the preferred product from both thermodynamic and kinetic points of view is HFCN + H. Therefore, reactions of nitrogen atoms with chloromethyl radicals release chlorine atoms as major products. The rate coefficient for the title reaction is estimated to be about 3.09 x 10(-13) cm3 s(-1) molecule(-1) at 300 K, a value four times smaller than the rate coefficient for its fluorine analogue.