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21.
Branko S. Jursic 《International journal of quantum chemistry》1997,61(1):93-100
An extensive computational study of the meal electron affinity was performed using the ab initio and density functional theory (DFT) methods. HF, MP2, MP3, MP4, QCISD, and QCISD(T) was used as computational methods, while the hybrid, local, and nonlocal DFT methods with the LYP, P86, PW91, and VWN correlation functionals were used. Two basis sets, one small and applicable to almost all metals (LanL2DZ) and one large [6-311 + + G(3df, 3 pd)] used only for small metals, were employed. The computed results were compared with the experimental data and the capabilities of the DFT methods to perform this study were discussed. © 1997 John Wiley & Sons, Inc. 相似文献
22.
Branko S. Jursic 《International journal of quantum chemistry》1996,58(1):41-46
Ab initio and density functional theory (DFT) methods have been applied to generated geometries of chemical systems built only from nitrogen and oxygen. The results of hybrid, local, and nonlocal DFT methods were compared with ab initio HF and MP2 methods. The suitability of DFT methods for modeling nitrogen-oxygen chemical systems is discussed. © 1996 John Wiley & Sons, Inc. 相似文献
23.
Branko S. Jursic 《Journal of computational chemistry》1996,17(7):835-840
The structures of two isomers, difluorodisulfane (FSSF) and thiothionylfluoride (SSF2), and the corresponding transition structure were generated with density functional theory (DFT) methods. Three groups of DFT methods were used: local (Local Spin Density Approximation, LSDA), nonlocal (local with gradient corrections; BLYP and BP86), and hybrid methods that include a mixture of Hartree-Fock (HF) exchange with nonlocal correlation (Becke3BLYP, Becke3P86). An extended basis set [6-311 + + G(3df)] was used for all calculations, although satisfactory results can be obtained with the 6-311G(d) basis set. The geometries obtained were compared with both restricted Hartree-Fock (RHF) calculated and experimentally obtained values. The energy outcome and the activation barrier for the isomerization were evaluated. It was determined that excellent geometries can be obtained with the Becke3B86 hybrid method, whereas for reasonable energies MP2 single-point calculations on these geometries are necessary. © 1996 by John Wiley & Sons, Inc. 相似文献
24.
Branko S. Jursic 《Theoretical chemistry accounts》1998,99(3):171-174
Ionization potentials, bond dissociation energies, and heat of formation for NH and NH+ molecular species as well as for their elements were computed with highly reliable quadratic complete basis set and Gaussian-2
ab initio methods. The results are compared with experimental results and the assurance of these ab initio approaches is assessed.
The same studies were also performed with three hybrid density functional methods (B3LYP, B3P86, and B3PW91) in combination
with variously sized basis sets. The computational results are discussed in light of density functional theory reliability
for exploring the potential energy of small polar molecular systems.
Received: 21 July 1997 / Accepted: 8 December 1997 相似文献
25.
van Eis MJ van Der Linde BS de Kanter FJ de Wolf WH Bickelhaupt F 《The Journal of organic chemistry》2000,65(14):4348-4354
In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway. 相似文献
26.
Sunil K. UpadhyayBranko S. Jursic 《Tetrahedron letters》2011,52(16):1835-1838
Tagged and activated d-glucose was introduced as a building block for branched oligosaccharides. This building block was the oligosaccharide branching point at which selectively the C-2 followed by the C-3 position can be glycosylated. After the activation of the C-1 position by oxidation of a thiophenyl group, the newly formed tagged oligosaccharide can be used as a glycoside donor. Synthetic procedures for the preparation of phthalimide-based tag molecules as well as tagged monosaccharides are presented. 相似文献
27.
Branko S. Jursic 《Journal of heterocyclic chemistry》2003,40(1):167-170
Preparation of 5,5′‐(pyridin‐2‐ylmethylene)dipyrimidinetrione from barbituric acid and 2‐pyridinecarbox‐aldehyde in any polar solvent is a straightforward synthetic procedure, while preparation of the dipyridine‐dibarbituric acid ylide from the same starting materials is sensitive to the reaction media, pH, and temperature. For both products, the formation of the reactive intermediate 2‐pyridin‐2‐ylmethylenepyrimidinetrione is certain and this intermediate is a cross road for the reaction to be directed in one way or other. The experimental evidence for the formation of this important intermediate, as well as synthetic procedures for the preparation of both condensation products are presented. 相似文献
28.
Branko S. Jursic 《Journal of heterocyclic chemistry》1995,32(5):1445-1455
A semiempirical AMI theoretical study was carried out to examine the very low reactivity of thiophene; for example, the high reactivity of thiophene 1-oxide as a diene in the Diels Alder reactions. The reactivities of cyclopentadiene, thiophene, thiophene 1-oxide, and thiophene 1,1-dioxide were studied as dienes in the reaction with ethylene, cyclopropene, and benzoquinone. Ethylene was chosen as a standard, while cyclopropene, with its high strain energy was released in the course of a reaction making it relatively reactive. The benzoquinone has a lower LUMO energy, making it a very reactive dienophile for the Diels-Alder reaction. Frontier molecular orbital energy gap between the reactants was considered, and the disadvantage of this approach in studying the reactivity was demonstrated. For all combinations, the corresponding transition structures are generated and the activation energies are estimated. The estimated activation barrier for sulfur dioxide elimination from the adduct was used to explain the failure to accumulate the cycloadduct in the reaction mixture. The obtained results are compared with experimental data when available. An excellent agreement of theory and experiment was obtained. 相似文献
29.
Branko S. Jursic 《Journal of heterocyclic chemistry》1998,35(6):1467-1471
Semiempirical and density functional theory computational studies were carried out with the target determining the reactivity of five membered heterocycles with heteroatoms in the 1 and 3 positions as dienes for Diels-Alder reactions. The relative reactivity was evaluated in their reaction with acetylene, ethylene, and cyclopropene as dienophiles for cycloaddition. Qualitative criteria such as uniformity of heterocycle bond orders, change of bond orders and frontier molecular orbital energies in transformation of reactants into transition state structures were used to determine the relative reactivity in comparison with furan. These results are compared with the computed activation barriers as well as with experimental findings, where available. If cycloaddition is feasible with these heterocycles, a new synthetic transformation of simple organic compounds to valuable prostaglandin derivatives can be accomplished. 相似文献
30.
Branko S Jursic 《Journal of Molecular Structure》1998,434(1-3):67-73
The HF, MP2, MP3, MP4, and QCISD ab initio methods were compared with local, hybrid, and gradient-corrected density functional theory (DFT) methods for computing structures and energies of N2F4 rotamers. In all DFT calculations 6-311 + G(2d) basis set was used. The generated structures energies of trans- and gauche-N2F4 rotamers, and their dissociation energies to nitrogen difluoride were compared with experimental data. Suitable hybrid and gradient-corrected DFT methods for determining structures and energies for these and similar molecular systems were discussed. 相似文献