共查询到20条相似文献,搜索用时 31 毫秒
1.
The selectivity of attacking sites and the reaction mechanisms of the bis-addition of methyl azide with its corresponding azafulleroid (C 60NCH 3) have been investigated using AM1 semi-empirical and density functional methods. The whole reaction processes can be divided into two stages. The first stage is the 1,3-dipolar cycloaddition (1,3-DC) reaction of methyl azide with C 60NCH 3 giving rise to a triazoline intermediate and the second is the N 2 elimination. Based on the charge distributions, four patterns of the addition sites have been discussed. In view of the energy barriers, two kinds of 6–6 double bonds, which are in the most and the second vicinities of the –NCH 3 addend group of the C 60NCH 3, are the two most possible attack sites in the reaction of 1,3-DC. The analyses of the π-orbital axis vector (POAV) and the deformation and interaction energies indicate that it is the favorable interaction energy rather than the strain release that dominates the two preferential attacking patterns. The subsequent thermal elimination of N 2 takes place via two steps in which the breaking of N–N single bond precedes the cleavage of the C–N bonds of the unsubstituted N atom. The N 2 elimination occurs simultaneously with the formation of the new C–N bonds (corresponding to the substituted N atom), giving rise to two isomers of the bisadducts. One is a double azafulleroid with two N atoms bonding to two consecutive 5-6 junctions of the same pentagon, and the other with two N atoms bonding to two alternate 5-6 junctions of the same pentagon. The analysis of the energy results shows that although the former reaction is preferred to some extent, both of the two reactions can take place and both of the two bisadducts are in principle obtainable. 相似文献
2.
丁二烯-丙烯腈共聚物碳-碳双键的选择性加氢张邦华,王光,周庆业,郝广杰,宋谋道,张莹(南开大学高分子化学研究所,天津,300071)关键词丁二烯-丙烯腈共聚物,氯化三苯基膦铑,均相催化,选择性加氢通过催化加氢对不饱和高聚物进行化学改性是提高大分子的物... 相似文献
3.
The equilibrium structures and relative stabilities of BN-doped fullerenes C 70−2x(BN) x ( x=1–3) have been studied at the AM1 and MNDO level. The most stable isomers of C 70−2x(BN) x have been found out and their electronic properties have been predicted. The calculation results show that the BN substituted fullerenes C 70−2x(BN) x have considerable stabilities, though they are less stable than their all carbon analog. For C 68BN, the isomers whose BN is located in the most chemically active bonds of C 70 (namely B and A) are among the most stable species, of which B is predicted to be the ground state. The stabilities of C 68BN decrease and the dipole moments increase with increasing the distance between the heteroatoms. For C 66(BN) 2, the lowest energy species is the isomer in which the B–N–B–N bond is formed; For C 64(BN) 3, the most stable species should have three BN units located in the same hexagon to form B–N–B–N–B–N ring. The ionization potentials and the affinity energies of the most stable species of BN-doped C 70 are almost the same as those of C 70 because of the isoelectronic relationship. The ionization potentials and affinity energies depend on the relative position of the heteroatoms in C 68BN, the chemical reactivities of the isomers whose heteroatoms are well separated should differ significantly from their all carbon analog. 相似文献
4.
Spatial structure of six β-substituted enones, with common structure R 1O–CR 2CH–COCF 3, were R 1 = C 2H 5, R 2 = H (ETBO); R 1 = R 2 = CH 3 (TMPO); R 1 = C 2H 5, R 2 = C 6H 5 (ETPO); R 1 = C 2H 5, R 2 = 4- O 2NC 6H 4 (ETNO); R 1 = C 2H 5, R 2 = C(CH 3) 3 (ETDO) were investigated by 1H and 19F NMR, infrared spectroscopy and AM1 calculations. NMR spectra revealed that enones (MBO), (ETBO) and (TMPO) are exclusively (3 E) isomers, whereas in (ETPO), (ETNO) and especially in (ETDO) the percentage of (3 Z) isomers is significant and depends on the nature of solvents. Conformational behaviour of studied enones are determined by the rotation around of CC double bond, C–C and C–O single bonds (correspondingly trifluoroacetyl and alkoxy groups), and ( EZZ) conformer being the most stable in all cases. IR spectra revealed that with the exception of (ETDO) ( EZZ) conformer is most populated in all cases. Bulky substituents like phenyl or tert-butyl group at β-position of enone result in the equilibrium mainly between ( EZZ) and ( ZZZ) forms, whereas β-hydrogen and β-methyl substituents determine the equilibrium between ( EZZ) and ( EEZ) or ( EZE) conformers. 相似文献
5.
The directed oligomerization of propene and 1-hexene was carried out with a series of Cp′(C 5H 5)ZrCl 2 and Cp 2′ZrCl 2 pre-catalysts (Cp′=C 5HMe 4, C 4Me 4P, C 5Me 5, C 5H 4tBu, C 5H 3-1,3- tBu 2, C 5H 2-1,2,4- tBu 3) together with (C 5H 5) 2ZrCl 2. Oligomers in the molar mass range 300–1500 g/mol for propene and 200–3000 g/mol for 1-hexene were synthesized at 50 °C. The majority of oligomer molecules contain a double-bond end group. Oligomer characterization was carried out by gel permeation chromatography (GPC), 1H and 13C NMR. Vinylidene double bonds (from β-hydrogen elimination) are solely found for the tert-butyl-substituted zirconocenes and for most of the unsymmetrical methyl-substituted Cp′(C 5H 5)ZrCl 2 systems (except Cp′=phospholyl). With (C 4Me 4P)(C 5H 5)ZrCl 2 and with the symmetrical methyl-containing Cp 2′ZrCl 2 pre-catalysts, also vinyl end groups (from β-methyl elimination) are observed in the case of oligopropenes. The vinylidene/vinyl ratio depends on the ligand and the vinyl content increases from C 5HMe 4 (65/35) over C 4Me 4P (61/39) to C 5Me 5 (9/91). The phospholyl zirconocenes and (C 5HMe 4) 2ZrCl 2 also exhibit chain-transfer to aluminum thereby giving saturated oligomers. 相似文献
6.
Hydrogen and fluorine addition reactions with C 28( Td) have been investigated by the density function theory method at B3LYP/6-31G level. The interaction potential between C 28( Td) and atom X (X=H and F) shows that there are three possible stable isomers of C 28( Td)X (X=H and F) and the average binding energy calculations suggest that C 28( Td)H 4 is the most stable hydrogen adduct among C 28( Td)H n ( n=1–28). Furthermore, by comparisons of the energy between C 28( Td)H and C 28( Cs)H we found that the former are more stable than the later, and the structural and energy analysis further indicate that C 28( Cs)H is only with a small distortion of C 28( Td)H symmetry. In addition, the transition states, as well as reaction pathways of X transfer reactions between different key points on C 28( Td) representative patch are given to explore the possible reaction mechanism. 相似文献
7.
Molecules of C 12H 4F 8N 2 crystallize in the orthorhombic space group P2 12 12 1 with cell constants a=9.200(1), b=10.896(1), c=23.178(3) Å and V=2323.4(5) Å 3. There are two molecules in the asymmetric unit which have D 2 symmetry. However these two molecules have C 2 symmetry in central C–C bonds, separately. Intramolecular steric repulsions between F atoms and N–HF hydrogen bonds have very much affected the molecular conformation. The mean dihedral angle between intramolecular phenyl rings is 119.2(1)°. The N–C bonds have lengths 1.363(4)–1.407(4) Å with a mean of 1.388 Å. This is shorter than the conventional C–N (1.47(1) Å) bond length due to π-electron delocalizations (F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen, R. Taylor, J. Chem. Soc. Perkin Trans. II (1987) S1–S19). The molecular structure of the title compound was also investigated by IR spectroscopy. It was shown that the IR spectra are in agreement with the crystal structure. On the other hand, theoretical and semi-emprical molecular mechanic calculations were carried out to obtain the most probable low-energy conformations by using MM3, PM3 and AM1 programs. 相似文献
8.
A novel pre-column derivatization method for the quantitative determination of ginsenosides by HPLC with fluorescence detection was established. The double bond at the C 24–C 25 position of ginsenoside was converted into an aldehyde group by means of ozonolysis. Then the aldehyde group reacts with FMOC-hydrazine forming the ginsenoside FMOC-hydrazone. The derivatized products were separated by RP-HPLC with gradient elution. The detection limits of ginsenosides Rg 1 and Rb 1 were 2.0 ng (about 2.5 pmol) and 1.0 ng (about 0.9 pmol), respectively. This method can be used for all ginsenosides having the C 24–C 25 double bond. 相似文献
9.
In the photochemical reaction of anthraquinone triplet with both tertiary alcohols and tert.Bu-benzene in C 6H 6 at λ 334 nm not only C---H (or O---H) bonds but C---C bonds are also broken, yielding CH 3, and R 1C(R 2)OH (or C 6H 5C(CH 3) 2) radicals, at room temperature. 相似文献
10.
Theoretical calculations (DFT, MP2) are reported for up to four sets of reaction products of trimethylphosphine, (CH 3) 3P, each with H 2O, HCl and HF together with DFT calculations on up to three sets of reaction products of substituted phosphonium cations, (CH 3) 3P–R +. These products comprise (a) P(III) normal complexes (CH 3) 3PHY, (b) P(IV) ‘reverse’ complexes Y(H–CH 2) 3P–R, (c) P(IV) ylidic complexes YHCH 2(CH 3) 2P–R and (d) P(V) covalent compounds Y–P(CH 3) 3–R for Y=HO, Cl and F and R=H, CH 3, C 2H 5, C 2H 4OH and C 2H 4OC:OCH 3. Calculations are carried out at the B3LYP/6-31+G(d,p) level in all cases and also at the MP2/6-31+G(d,p) level for systems in which R=H. Minimum energy structures are determined for predicted complexes or structures and geometrical properties, harmonic vibrations and BSSE corrected binding energies are reported and compared with the limited experimental information available. Potential energy scans predict equilibria between covalent trigonal bipyramidal P(V) forms and reverse complexes comprising hydrogen bonded or ion pair, tetrahedral P(IV) forms separated by low potential energy barriers. Similar scans are also reported for equilibria between reverse complexes and ylidic complexes for Y=OH and R=CH 3, C 2H 5, C 2H 4OH and C 2H 4OC:OCH 3. Corrected binding energies, structures and values of harmonic modes are discussed in relation to bonding The names ‘pholine’ and ‘acetylpholine’ are suggested for phosphorus analogues to choline and acetylcholine. 相似文献
11.
The spectral analysis indicates that all isomers of C 60O, C 70O and C 60O 2 have an epoxide-like structure (an oxygen atom bridging across a C–C bond). According to the geometrical structure analysis, there are two isomers of fullerene monoxide C 60O (the 5,6 bond and the 6,6 bond), eight isomers of fullerene monoxide C 70O and eight isomers of fullerene dioxide C 60O 2. In order to simulate the real reaction conditions at 300 K, the calculation of the different isomers of C 60O, C 60O 2 and C 70O fullerene oxides was carried out using the semiempirical molecular dynamics method with two different approaches: (a) consideration of the geometries and thermodynamic stabilities, and (b) consideration of the ozonolysis mechanism. According to the semiempirical molecular dynamic calculation analysis, the probable product of this ozonolysis reaction is C 60O with oxygen bridging over the 6–6 bond (C 2v). The most probable product in this reaction contains oxygen bridging across in the upper part of C 70 (6–6 bond in C 70O-2 or C 70O-4) an epoxide-like structure. C 60O 2-1, C 60O 2-3 and C 60O 2-5 are the most probable products for the fullerene dioxides. All of these reaction products are consistent with the experimental results. It is confirmed that the calculation results with the semiempirical molecular dynamics method are close to the experimental work. The semiempirical molecular dynamics method can offer both the reaction temperature effect by molecular dynamics and electronic structure, dipole moment by quantum chemistry calculation. 相似文献
12.
The reaction of [(C 6H 6)RuCl 2] 2 with 7,8-benzoquinoline and 8-hydroxyquinoline in methanol were performed. The obtained complexes have been studied by IR, UV–VIS, 1H and 13C NMR spectroscopy and X-ray crystallography. In the reaction with 8-hydroxyquinoline the arene ruthenium(II) complex oxidized to Ru(III). The electronic spectra of the obtained compounds have been calculated using the TDDFT method. Magnetic properties of [Ru(C 9H 6NO) 3] · CH 3OH complex suggest the antiferromagnetic coupling of the ruthenium centers in the crystal lattice. EPR spectrum of [Ru(C 9H 6NO) 3] · CH 3OH compound indicates single isotropic line only characteristic for Ru 3+ with spin equal to 1/2. 相似文献
13.
Photocatalytic CO 2 reduction to C 1 fuels is considered to be an important way for alleviating increasingly serious energy crisis and environmental pollution. Due to the environment-friendly, simple preparation, easy formation of highly-stable metal-nitrogen(M-N x) coordination bonds, and suitable band structure, polymeric carbon nitride-based single-atom catalysts(C 3N 4-based SACs) are expected to become a potential for CO 2 reduction under visible-light irradiation. In this review, we summarize the recent advancement on C 3N 4-based SACs for photocatalytic CO 2 reduction to C 1 products, including the reaction mechanism for photocatalytic CO 2 reduction to C 1 products, the structure and synthesis methods of C 3N 4-based SACs and their applications toward photocatalytic CO 2 reduction reaction(CO 2RR) for C 1 production. The current challenges and future opportunities of C 3N 4-based SACs for photoreduction of CO 2 are also discussed. 相似文献
14.
The complex triplet potential energy surface of the C 2H 3N system is investigated at the UB3LYP and CCSD(T) (single-point) levels in order to explore the possible reaction mechanism of C 2H 3 radical with N( 4S). Eleven minimum isomers and 18 transition states are located. Possible energetically allowed reaction pathways leading to various low-lying dissociation products are obtained. Starting from the energy-rich reactant C 2H 3+N( 4S), the first step is the attack of the N atom on the C atom having one H atom attached in C 2H 3 radical and form the intermediate C 2H 3N(1). The associated intermediate 1 can lead to product P 1 CH 2CN+H and P 2 3CH 2+ 3HCN by the cleavage of C–H bond and C–C bond, respectively. The most favorable pathway for the C 2H 3+N( 4S) reaction is the channel leading to P 1, which is preferred to that of P 2 due to the comparative lower energy barrier. The formation of P 3 3C 2H 2+ 3NH through hydrogen-abstraction mechanism is also feasible, especially at high temperature. The other pathways are less competitive comparatively. 相似文献
15.
The details of weak C–H π interactions that control several inter and intramolecular structures have been studied experimentally and theoretically for the 1:1 C 2H 2–CHCl 3 adduct. The adduct was generated by depositing acetylene and chloroform in an argon matrix and a 1:1 complex of these species was identified using infrared spectroscopy. Formation of the adduct was evidenced by shifts in the vibrational frequencies compared to C 2H 2 and CHCl 3 species. The molecular structure, vibrational frequencies and stabilization energies of the complex were predicted at the MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels. Both the computational and experimental data indicate that the C 2H 2–CHCl 3 complex has a weak hydrogen bond involving a C–H π interaction, where the C 2H 2 acts as a proton acceptor and the CHCl 3 as the proton donor. In addition, there also appears to be a secondary interaction between one of the chlorine atoms of CHCl 3 and a hydrogen in C 2H 2. The combination of the C–H π interaction and the secondary ClH interaction determines the structure and the energetics of the C 2H 2–CHCl 3 complex. In addition to the vibrational assignments for the C 2H 2–CHCl 3 complex we have also observed and assigned features owing to the proton accepting C 2H 2 submolecule in the acetylene dimer. 相似文献
16.
A molecular complex of fullerene C 60 with triptycene, TPC·C 60 is obtained. The complex has a three-dimensional packing of C 60 molecules. According to the IR spectra, the freezing of free rotation of C 60 molecules in the complex is maintained up to 360 K. The XP-spectra of TPC·C 60 show the suppression of π–π * transitions of TPC phenylene rings. The separation of C 60 molecules by TPC ones in TPC·C 60 results in low intensity of the C 60 transitions in the 420–500 nm range in an optical spectrum. This absorption is assumed as that attributed to intermolecular transitions between adjacent C 60 molecules. 相似文献
17.
The pyrolysis mechanism of important intermediate 1-hexene of carbon matrix precursor cyclohexane was studied theoretically. Possible reaction paths were designed based on the potential surface scan and electron structure of the initial C–C bond breaking reactions. Thermodynamic and kinetic parameters of the possible reaction paths were computed by UB3LYP/6-31+G* at different temperature ranges. The results show that 1-hexene pyrolyzes at 873 K. When below 1273 K, the major reaction paths are those that produce C 3H 4, and above 1273 K, the major reaction paths are those that produce C 3H 3 from the viewpoint of thermodynamics. From the viewpoint of kinetics, the major product is C 3H 3, it results from the pyrolysis reaction of 1-hexene cracking bond C 3–C 4 and generating C 3H 5 and C 3H 7 with the activation energy Δ E0≠θ=296.32 kJ/mol. Kinetic results also show that product C 3H 4 accompany simultaneously, which is the side reaction starting from the pyrolysis of 1-hexene forming C 4H 7 and C 2H 5 with the activation energy of 356.73 kJ/mol. When reaching 1473 K, the rate constant of the rate-determining steps of these two reaction paths do not show much difference, which means both the reaction paths exist in the pyrolysis process at the high temperature. The above results are basically in accordance with mass spectrum analysis and far more specific. 相似文献
18.
Palladium–copper catalysed cross-coupling reactions of tetracholoroethene with terminal acetylenes RCCH (R=SiMe 3, C 6H 5, C 6H 4CN-4) in refluxing triethylamine afford the corresponding tetraethynylethenes in 30–60% isolated yields. The reaction of 1,6-bis(trimethylsilyl)-3,4-bis(trimethylsilylethynyl)-hex-3-ene-1,5-diyne with [Co 2(CO) 6(L 2)] [L 2=(CO) 2 or μ-dppm] affords complexes in which one or two ( trans) acetylene moieties are coordinated by a dicobalt fragment. 相似文献
19.
Though the H-bond is well characterized as a D–H:A three-center-four-electron interaction, the formulation of a general H-bond theory has turned out to be a rather formidable problem because of the extreme variability of the bonds formed (for instance, O–HO energies range from 0.1 to 31 kcal mol −1). This paper surveys our previous contributions to the problem, including: (a) the H-bond chemical leitmotifs (CLs), showing that there are only four classes of strong H-bonds and one of moderately strong ones; (b) the PA/pKa equalization principle, showing that the four CLs forming strong H-bonds are actually molecular devices apt to equalize the acid–base properties (PA or p Ka) of the H-bond donor and acceptor groups; (c) the driving variable of the H-bond strength, which remains so identified as the difference Δp Ka=p KAH(D–H)−p KBH(A–H +) or, alternatively, ΔPA=PA(D −)−PA(A); and, in particular, (d) the transition-state H-bond theory (TSHBT), which interprets the H-bond as a stationary point along the complete proton transfer pathway going from D–HA to DH–A via the DHA transition state. TSHBT is verified in connection with a series of seven 1-(X-phenylazo)-2-naphthols, a class of compounds forming a strong intramolecular resonance-assisted H-bond (RAHB), which is switched from N–HO to NH–O by the decreasing electron-withdrawing properties of the substituent X. The system is studied in terms of: (i) variable-temperature X-ray crystallography; (ii) DFT emulation of stationary points and full PT pathways; (iii) Marcus rate-equilibrium analysis correlated with substituent LFER Hammett parameters. 相似文献
20.
IR spectroscopy was coupled with the matrix isolation technique to study the molecular complex formed between C 3O 2 and HCl and its photodissociation. The vibrational frequencies of the complex were compared with those of HCl and C 3O 2 monomers. For C 3O 2, a bent structure was characterized in the solid environment. The vibrational frequencies were calculated in the 4000–400 cm−1 range using an ab initio method at the MP2/6-31G** level for the most stable complex; these frequencies describe the hydrogen interaction with the central carbon atom of C3O2 (T complex). The measured shifts between the vibrational mode frequencies of the complex and monomers were in good agreement with the calculated values. Broad-band UV irradiation ( > 230 nm) of the T complex leads preferentially to ketene chloride and carbon monoxide. Ketene chloride formation can be explained by the reaction between HCl and the carbene C2O, which results from photo-dissociation at the C=CO bond of C3O2. 相似文献
|