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1.
In the present theoretical work we have explored mechanisms of dissociation reactions of the vinyl radical in the A 2A″ state (C 2H 3 (A 2A″)) and examined possible pathways for nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+). In the calculations we used the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with the cc-pVDZ and cc-pVTZ basis sets. Mechanisms for the following three dissociation channels of C 2H 3 in the A 2A″ state were explored: (1) C 2H 3 (A 2A″) → C 2H 2 ( trans, 3A u) + H, (2) C 2H 3 (A 2A″) → C 2H 2 ( cis, 3A 2) + H, and (3) C 2H 3 (A 2A″) → H 2CC ( 3A 2) + H. The CASSCF and CASPT2 potential energy curve calculations for the C 2H 3 (A 2A″) dissociation channels (1)–(3) indicate that there is neither transition state nor intermediate for each of the channels. At the CASPT2//CASSCF/cc-pVTZ level, the dissociation energies for channels (1)–(3) are predicted to be 84.3, 91.1, and 86.9 kcal/mol, respectively. For a recently observed nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+) + H [J. Chem. Phys. 111 (1999) 3783], two previously suggested internal conversion (IC) pathways were examined based on our CASSCF and CASPT2 calculations. Our preliminary CASSCF and CASPT2 calculations indicate that the assumed IC pathway via the twisted C 2H 3 (A 2A ′) structure might be feasible. The CASSCF/cc-pVTZ geometry optimization and frequency analysis calculations were performed for the four C 2v bridge structures in the 2B 2, 2A 2, 2B 1, and 2A 1 states along the pathways of the 1 2A ′ (X 2A ′), 1 2A″ (A 2A″), 2 2A″, and 2 2A ′ states of C 2H 3, respectively, and the CASPT2//CASSCF/cc-pVTZ energetic results indicate that the assumed IC pathway, via a C 2v ( 2A 2) structure and then 2A 2/ 2A 1 surface crossing, be not feasible since at their excitation wavelengths (327.4 and 366.2 nm) the C 2v ( 2A 2) structure could not be accessed. 相似文献
2.
Synthesis of (2 R,3 S,4 S)-4-aryl-3-hydroxyprolinols has been established starting from 2-benzyloxymethylpyrrolidin-2-one framework, which is derived from commercially available trans-(2 S,4 R)-4-hydroxyproline. The single diastereomer having a trans–cis relative configuration with C 2 and C 3 and C 3 and C 4 is constructed in two one-pot functional group transformations of Grignard addition/dehydration and epoxidation/isomerization as the key steps in moderate yield. 相似文献
3.
A molecular thermodynamic model developed previously for fluids of chain-like molecules has been extended to correlate the pVT behavior of ionic liquids and the solubilities of gases such as CO 2, C 3H 6, C 3H 8, C 4H 10 in various ionic liquids. The relative deviation between the calculated molar volume and experimental data is less than 0.2%. It is shown that this equation of state can be used to correlate the solubility of CO 2 in ionic liquids with only one temperature-independent adjustable interaction parameter, and the accuracy of the correlation can be further improved using two temperature-independent adjustable parameters. The water content of ionic liquids has a large influence on the calculated results. For systems with water content lower than 0.1%, the average relative deviations of bubble point pressure are 3.14 and 4.90% using two parameters and one parameter, respectively. For systems containing C 3H 6, C 3H 8 and C 4H 10 two temperature dependent adjustable parameters are needed to obtain a good fit, and the corresponding deviation of the gas solubility is less than 2%, except for C 3H 8. 相似文献
4.
Treatment of 1,2- trans-C 5H 8(PCl 2) 2 with 1,2-C 2H 4(NHPr- i) 2 gave the C2-symmetric perhydro-1,6,2,5-diazaphosphocine C 5H 8{P(Cl)N(Pr- i)CH 2} 2- cyclo, which produced dissymmetric C 5H 8(PPh 2){P[N(Pr- i)CH 2] 2- cyclo} on further reaction with PhMgBr. Cleavage of the P---N bonds with gaseous HCl afforded C 5H 8(PPh 2)(PCl 2), which was converted to C 5H 8(PPh 2){P(OPh) 2} 2 by reaction with phenol. All chiral P, P derivatives were obtained as racemates as well as resolved (1 R,2 R)- and (1 S,2 S)-enantiomers. 相似文献
5.
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
6.
The atomic cations of Sr and Mo have been observed to add sequentially up to four molecules of C 60 in helium at 0.35 Torr and room temperature in the flow tube of a modified inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The available center-of-mass energy in collision-induced dissociation experiments of approximately 1.3 eV failed to remove C 60 from M +(C 60) 4. A structure is proposed for M +(C 60) 4 cations in which the bonding involves η 6 interaction of the metal with the C 60 ligands and η 2-to-η 2 interactions between the C 60 ligands. 相似文献
7.
A structural study of odd-numbered n-alkane (C n) binary mixtures (C 21 : C 23) was carried out on powder samples using a Guinier-de Wolff camera with increasing concentration of n-C 23 at 293 K. Despite the reports in the literature, these molecular alloys do not form an orthorhombic continuous homogeneous solid solution to C21 from C23 at “low temperature”. Instead, as already observed in two even-numbered Cn systems, X-ray diffraction results show the existence of seven solid solutions as the molar concentration of C23 increases: four terminal solid solutions, denoted β0(C21)β0(C23), isostructural with the “low temperature” phase of pure C21 and C23 (Pbcm), β′0(C21) and β′0(C23), identical to the phase β′0 which appears in pure C23 above the δ transition, and three orthorhombic intermediate solid solutions, designated β″1, β′1 and β″2. On the basis of powder X-ray photographs, the phases β″1 and β″2 (C21 : C23) are indistinguishable, and they are isostructural with the intermediate solid solution β″ of the even-numbered Cn binary systems (C22 : C24) and (C24 : C26). The phase β′1(C21 : C23) is also isostructural with the two indistinguishable intermediate solid solutions β′1 and β′2 of the molecular alloys (C22 : C24) and (24 : C26). From this study and our other laboratory results, the sequences of appearance of the solid solutions and the structural identities between these phases are established at “low temperature” for all the binary molecular alloys of consecutive Cn (odd-odd, even-even or odd-even: 19 < n < 27) when increasing the solute concentration. 相似文献
8.
A supercritical fluid chromatographic (SFC) procedure for the quantitation of three major polyprenols present in the leaves of Ginkgo biloba was developed. In contrast to previously reported high-performance liquid chromatographic (HPLC) methods, the SFC method does not require extensive pre-purification for polyprenol analysis. The SFC analytical procedure described shows a very broad range of linearity and detects many known polyprenol isoprenologs with baseline separation. Dodecaprenol was used as the internal standard. The coefficient of variation of the method was 5.8% for the quantitation of C 85, C 90 and C 95 polyprenols. The SFC assay results showed that the content of polyprenols in ginkgo leaves were higher than the previously published values. In addition, the chromatogram of the highly concentrated leaf extract revealed the presence of an isoprenolog (C 120) not previously detected by HPLC methods. 相似文献
9.
(+)-(9 S)-Dihydroerythronolide A, 1, is prepared in 8 steps from macrolide 3 by exploiting the conformational preferences of the (5 E,11 E)-diene intermediate 2. The stereocontrolled introduction of the hydroxyl groups at C 6, C 11, and C 12 is achieved by osmylation, 2 → 13 and 15 → 1, while that at C 5 is obtained by a Zn(BH 4) 2 reduction, 13 → 14. 相似文献
10.
Likely candidates for the lowest potential energy minima of (C 60) nCa 2+, (C 60) nF − and (C 60) nI − clusters are located using basin-hopping global optimisation. In each case, the potential energy surface is constructed using the Girifalco form for the C 60 intermolecular interaction, an averaged Lennard–Jones C 60–ion interaction, and a polarisation potential, which depends on the first few non-vanishing C 60 multipole polarisabilities. We find that the ions generally occupy the interstitial sites of a (C 60) n cluster, the coordination shell being tetrahedral for Ca 2+ and F −. The I − ion has an octahedral coordination shell in the global minimum for (C 60) 6I −, however for 12 n 8 the preferred coordination geometry is trigonal prismatic. 相似文献
11.
By means of our proposed method for Hückel theory calculation, we have calculated the electronic structures of dihedral (D 5h, D 5d, D 6h, D 6d) fullerences, which are generated from icosahedral C 20, C 60, C 80, C 180, C 240 and C 540, respectively. From the calculated results of 1224 fullerence molecules, certain rules on the stability and chemical reactivity have been drawn for such types of dihedral fullerenes. 相似文献
12.
LnCl 3 (Ln=Nd, Gd) reacts with C 5H 9C 5H 4Na (or K 2C 8H 8) in THF (C 5H 9C 5H 4 = cyclopentylcyclopentadienyl) in the ratio of 1 : to give (C 5H 9C 5H 4)LnCl 2(THF) n (orC 8H 8)LnCl 2(THF) n], which further reacts with K 2C 8H 8 (or C 5H 9C 5H 4Na) in THF to form the litle complexes. If Ln=Nd the complex (C 8H 8)Nd(C 5H 9C 5H 4)(THF) 2 (a) was obtained: when Ln=Gd the 1 : 1 complex [(C 8H 8)Gd(C %H 9)(THF)][(C 8H 8)Gd(C 5H 9H 4)(THF) 2] (b) was obtained in crystalline form. The crystal structure analysis shows that in (C8H8)Ln(C5H9C5H4)(THF)2 (Ln=Nd or Gd), the Cyclopentylcyclopentadieny (η5), cyclooctatetraenyl (η8) and two oxygen atoms from THF are coordinated to Nd3+ (or Gd3+) with coordination number 10. The centroid of the cyclopentadienyl ring (Cp′) in C5H9C5H4 group, cyclooctatetraenyl centroid (COTL) and two oxygens (THF) form a twisted tetrahedron around Nd3+ (or Gd3+). In (C8H8)Gd(C5H9C5H4)(THF), the cyclopentyl-cyclopentadienyl (η5), cyclooctatetraenyl (η8) and one oxygen atom are coordinated to Gd3+ with the coordination number of 9 and Cp′, COT and oxygen atom form a triangular plane around Gd3+, which is almost in the plane (dev. -0.0144 Å). 相似文献
13.
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
14.
The harmonic frequencies and infrared intensities of C 9, C 11 and C 13 have been calculated using SCF and complete active space SCF (CASSCF) methods. The ordering of the harmonic frequencies in C 9 is predicted wrongly unless at least the π HOMO and LUMO are included in the active space. Infrared intensities depend crucially on the size of the active space. For linear odd-numbered clusters C 13 and larger, the computed SCF spectrum is qualitatively wrong. The recent observation of a band near 1809 cm −1 in the gas phase is explained using our CASSCF results on C 13. 相似文献
15.
The composition of (C 6Me 6)TiAl 2Cl 8−xEt x complexes in (C 6Me 6)TiAl 2Cl 8 + n Et 3Al ( n = 0.5-6) systems was studied by UV-Vis spectroscopy and the X-ray crystal structure of one of them, (η 6-C 6Me 6)Ti[(μ-Cl) 2(AlClEt)] 2 (IIa-2), has been determined. The complex crystallizes in the orthorhombic space group Pna2 1 with Z = 4 and lattice parameters a 15.634(3), b 11.355(2), c 14.417(2) Å. The ethyl groups of IIa-2 reside in outer positions of aluminate ligands farther away from the C 6Me 6 ligand. The other part of the complex does not differ remarkably from structures of other (arene)Ti II complexes. Negligible activity of (C 6Me 6)TiAl 2Cl 8 towards the butadiene cyclotrimerization is considerably increased by addition of 2.5–3.0 equivalents of Et 3Al. As follows from UV-Vis spectra, such systems contain mainly the (C 6Me 6)TiAl 2Cl 5Et 3 complex. It is suggested that the introduction of three Et substituents destabilizes the Ti-(η 6-C 6Me 6) bond so that the replacement of hexamethylbenzene by butadiene in the first step of a catalytic cycle becomes more feasible. 相似文献
16.
Resonance fluorescence spectra of CF 2( 1B 1, 040, K' = 9) excited at 253 7 nm have been observed in the photolysis of C 2F 4 using a low-pressure mercury lamp. At low C 2F 4 pressures, the spectra with a series of doublet hands from 254 to 400 nm were consistent with the transitions from 1B 1, 040, K'=9 to 1A 1, 0 v'20, K' = 8, 10, and also to 1A 1, 1 v'20, K' = 8, 10 The appearance of doublet bands (Δ K = ±1) provides clear evidence that the transition is of the perpendicular type. 相似文献
17.
Effect of solvent polarity on the aggregation behaviour of C 70 has been investigated in several mixed solvents using optical absorption, fluorescence, dynamic light scattering and scanning electron microscopic measurements and compared with those observed for the other fullerene analogue, C 60. It is seen that similar to C 60, aggregation of C 70 also requires the solvent polarity to exceed some critical value. In terms of solvent dielectric constant the critical solvent polarity, required for C 70 aggregation is found to be in the range of 27–31, which is much higher than that required for C 60 aggregation (12–14). The large difference in the critical solvent polarity required for C 60 and C 70 aggregation has been rationalized on the basis of the molecular shapes and the polarizabilities of two fullerene molecules. 相似文献
18.
The hydroxo-complexes [{PdR(PPh 3)(μ-OH)} 2] (R = C 6F 5 or C 6Cl 5) have been obtained by reaction of the corresponding [{PdR(PPh 3)(μ-Cl)}2] complexes with NBu 4OH in acetone. In this solvent, the reaction of the hydroxo-bridged complexes with pyrazole (Hpz) and 3,5-dimethylpyrazole (Hdmpz) in 1:2 molar ratio leads to the formation of the new complexes [{Pd(C 5F 5)(PPh 3)(μ-azolate)}2] and [{Pd(C 6Cl 5)(PPh 3)} 2(μ-OH)(μ-azolate)] (azolate = pz or dmpz). The reaction of the bis(μ-hydroxo) complexes with Hpz and Hdmpz in acetone in 1:1 molar ratio has also been studied, and the resulting product depends on the organic radical (C 6F 5 or C 6Cl 5) as well as the azolate (pz or dmpz). The identity of the isomer obtained has been established in every case by NMR ( 1H, 19F and 31P) spectroscopy. The reaction of the bis(μ-hydroxo) complexes with oxalic (H 2Ox) and acetic (HOAc) acids yields the binucle ar complexes [{PdR(PPh 3)}2(μ-Ox)] (R = C 6F 5 or C 6Cl 5) and [{Pd(C 6F 5)(PPh 3)(μ-OAc)}2], respectively. [{Pd(C 6F 5)(PPh 3)(μ-OH)} 2] reacts with PPh 3 in acetone in 1:2 ratio giving the mononuclear complex trans-[Pd(C 6F 5) (OH)(PPh 3) 2], whereas the pentachlorophenylhydroxo complex does not react with PPh 3, even under forcing conditions. 相似文献
19.
The stabilities of different isomers of C 60Br n have been calculated for n = 2 to 12. A general stereochemical pattern which emerges is the tendency to form strings created by the edge sharing of C 6Br 2 hexagonal faces. Stable structures are formed if these strings form loops, thereby eliminating string ends, which may involve the creation of C 6Br 3 hexagonal faces. A particularly stable structure is formed at C 60Br 6 in which the loop forms a C 10Br 6 fragment with a pentagonal pyramidal arrangement of six bromine atoms. Two isomers of C 60Br 12 are also particularly stable. One isomer contains two of these Br 6 pentagonal pyramids on opposite sides of the molecule, and the other isomer contains a single large loop wrapped around the middle of the molecule. 相似文献
20.
IntroductionTherecentdiscoveryofaclassofcarboncontainingmoleculesknownasthefulereneshasproducedaseriesofmaterialswithawideran... 相似文献
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