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1.
Activation barriers and reaction energetics for the three main classes of 1,3-dipolar cycloadditions, including nine different reactions, were evaluated with the MPW1K and B3LYP density functional methods, MP2, and the multicomponent CBS-QB3 method. The CBS-QB3 values were used as standards for 1,3-dipolar cycloaddition activation barriers and reaction energetics, and the density functional theory (DFT) and MP2 methods were benchmarked against these values. The MPW1K/6-31G* method and basis set performs best for activation barriers, with a mean absolute deviation (MAD) value of 1.1 kcal/mol. The B3LYP/6-31G* method and basis set performs best for reaction enthalpies, with a MAD value of 2.4 kcal/mol, while the MPW1K method shows large errors for reaction energetics. The MP2 method gives the expected systematic underestimation of barriers. Concerted and nearly synchronous transition structures are predicted by all DFT and MP2 methods. Also reported are revised estimated 0 K experimental activation enthalpies for a standard set of hydrocarbon pericyclic reactions and updated comparisons to experiment for DFT, ab initio, and multicomponent methods. B3LYP and MPW1K methods with MAD values of 1.5 and 2.1 kcal/mol, respectively, fortuitously outperform the multicomponent CBS-QB3 method, which has a MAD value of 2.3. The MAD value of the O3LYP functional improves to 2.4 kcal/mol from the previously reported 3.0 kcal/mol. 相似文献
2.
A series of computational approaches, based on the global and local indexes defined in the context of the DFT, at the B3LYP/6-31G(d) computational level, were investigated to elucidate the regiochemistry and the energetics of the mesitonitrile oxide 1,3-dipolar cycloaddition with anthracene and the aza-analogue acridine. The results are in agreement with the observed regioselectivity and are in contrast with the ones predicted in terms of FMO theory. 相似文献
3.
Simple and efficient strategies toward the synthesis of trisubstituted pyrrolizidines and disubstituted oxazolidine systems by 1,3-dipolar cycloaddition reactions using arylaldehydes and α-amino acids have been developed, followed by a one-pot, three-component strategy. Electron-deficient dipolarophiles, chalcones, were reacted with nonstabilized azomethine ylides derived from arylaldehyde and L-proline in dry dimethyl formamide, leading to substituted pyrrolizidines. The route to substituted oxazolidines involved cycloaddition to the C?O bond of a second molecule of the aldehyde. The structures and stereochemistry of the cycloadducts were established by infrared (IR), NMR spectroscopy, and single-crystal x-ray crystallographic analyses. Condensed Fukui functions and local electrophilicity indices have been computed to characterize the reactive sites and predict the preferred interactions of azomethine ylides to planar chalcones. The softness-matching indices have been evaluated to determine the regioselectivity of the cycloaddition reactions. The theoretical predictions were found to be in complete agreement with the experimental results, implying that the density functional theory (DFT)-based reactivity indices correctly predict the regioselectivities of 1,3-dipolar cycloadditions of azomethine ylides to planar chalcones. The frontier molecular orbital (FMO) energies, electronic chemical potentials, chemical hardness, chemical softness, and global electrophilicity indices of azomethine ylides have been calculated at the DFT/B3LYP/6-31 + G (d, p) level of theory. 相似文献
4.
The molecular structure and conformational stability of CH2CHCH2X (X=F, Cl and Br) molecules were studied using ab initio and density functional theory (DFT) methods. The molecular geometries of 3-fluoropropene were optimized employing BLYP and B3LYP levels of theory of DFT method implementing 6-311+G(d,p) basis set. The MP2/6-31G*, BLYP and B3LYP levels of theory of ab initio and DFT methods were used to optimize the 3-chloropropene and 3-bromopropene molecules. The structural and physical parameters of the molecules are discussed with the available experimental values. The rotational potential energy surface of the above molecules were obtained at MP2/6-31G* and B3LYP/6-311+G(d,p) levels of theory. The Fourier decomposition of the rotational potentials were analyzed. The HF/6-31G* and MP2/6-31G* levels of theory have predicted the cis conformer as the minimum energy structure for 3-fluoropropene, which is in agreement with the experimental values, whereas the BLYP/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels of theory reverses the order of conformation. The ΔE values calculated for 3-chloropropene at MP2/6-31G*, BLYP/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels of theory show that the gauche form is more stable than the cis form, which is in agreement with the experimental value. The same levels of theory have also predicted that the gauche form is stable than cis for 3-bromopropene molecule. The maximum hardness principle has been able to predict the stable conformer of 3-fluoropropene at HF/6-31G* level of theory, but the same level of theory reverses the conformational stability of 3-chloropropene and 3-bromopropene molecules and MP2/6-31G* level of theory predicted the stable conformer correctly. 相似文献
5.
Theoretical Study of Mechanism and Regioselectivity of 1,3-dipolar Cycloaddition of N-[methyl]-C-[5-nitro-2-furyl] Nitrilimine with Dimethyl 7-oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylate
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Farid Moeinpour 《化学物理学报(中文版)》2010,23(2):165-168
The mechanism and regioselectivity of 1,3-dipolar cycloaddition of N-[methyl]-C-[5-nitro-2-furyl] nitrilimine with dimethyl 7-oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylate were investigated using activation energy calculations and density functional theory-based re-activity indexes. The reaction proceeds by an asynchronous concerted mechanism. The calculations are performed at the B3LYP/6-31G(d) level of theory and the obtained results are in agreement with experimental outcome. 相似文献
6.
7.
The mechanism for the 1,3-dipolar cycloaddition of benzonitrile oxide toward ethynyl and propynylboronate has been studied by using density functional theory (DFT) at B3LYP/6-31G* level. These cycloadditions are concerted [3+2] processes. The presence of the two oxygens on the boronic ester precludes the participation of the boron atom on [3+3] processes. The two regioisomeric channels associated to the formation of the isoxazoles bearing the boronic ester unit on the 4- or 5-positions have been characterized. The B3LYP/6-31G* activation parameters are in acceptable agreement with the experiments, allowing to explain the factors controlling these regioselective cycloadditions. 相似文献
8.
C-甲基硝酮与硝基乙烯1,3-偶极环加成反应及其溶剂效应的理论研究 总被引:2,自引:0,他引:2
用密度泛函B3LYP方法研究了硝基乙烯与C-甲基硝酮的1,3-偶极环加成反应, 并利用自洽反应场方法(SCRF)计算了环已烷与乙腈这两种溶剂分别对反应所产生的 影响。该反应进行时反应物的接近有四种方式,对气相情况下和上述两种溶剂中的 反应物、四种可能产物及其相应过渡态和反应前期复合物构型分别进行了优化并计 算了振动频率。四个反应均为放热反应,且均具有很低的反应势垒,四种产物均容 易生成。但在气相反应和以环已烷为溶剂的情况下,生成的产物中endo-4型产物略 占优势;而在乙腈溶剂中得到endo-5型略占优势的产物。 相似文献
9.
10.
Zeghada S Bentabed-Ababsa G Derdour A Abdelmounim S Domingo LR Sáez JA Roisnel T Nassar E Mongin F 《Organic & biomolecular chemistry》2011,9(11):4295-4305
Reactions were performed from aryl azides on the one hand, and activated alkenes coming from β-dicarbonyl compounds or malonodinitrile on the other hand, either with recourse to conventional heating or to microwave activation, to afford 1-aryl-1H-1,2,3-triazoles. The mechanism and the regioselectivity of the reactions involving β-dicarbonyl compounds have been theoretically studied using DFT methods at the B3LYP/6-31G* level: they are domino processes comprising a tautomeric equilibrium of the β-dicarbonyl compounds with their enol forms, a 1,3-dipolar cycloaddition of the enol forms with the aryl azides (high activation energy), and a dehydration process (lower activation energy). The effect of non-conventional activation methods on the degradation of 1,2,3-triazolines was next studied experimentally. Finally, some of the 1,2,3-triazoles such synthesized were evaluated for their bactericidal and cytotoxic activities. 相似文献
11.
Abdelmalek Khorief Nacereddine Wassila Yahia Samir Bouacha Abdelhafid Djerourou 《Tetrahedron letters》2010,51(19):2617-121
A theoretical study of the regio- and stereoselectivities of the 1,3-dipolar cycloaddition of C-diethoxyphosphoryl-N-methylnitrone with substituted alkenes (allyl alcohol and methyl acrylate) is carried out using DFT at the B3LYP/6-31G(d,p) level of theory. The FMO analysis and DFT-based reactivity indices confirmed the experimental ortho regioisomeric pathway. Potential energy surface analysis shows that these 1,3-dipolar cycloaddition reactions favor the formation of the ortho-trans cycloadduct in both cases. The obtained results are in agreement with experimental data. 相似文献
12.
Jalbout AF Jiang Z Abou-Rachid H Najat Benkaddour N 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(3):603-609
Density functional theory (DFT) calculations at the B3LYP/6-311G* theoretical level have been performed to study the 1,3-dipolar cycloaddition (1,3-DC) reactions between indenone (1) and different 1,3-dipoles (diazomethane and N-methyl C-methoxy carbonyl nitrilimine, compounds 2 and 3, respectively). The geometrical and energetic properties were analysed for the different reactives, transition states and cycloadducts formed (compounds 4-11). The reactions proceed in the gas-phase by an asynchronous concerted mechanism, yielding different regiochemistry dependent on the 1,3-dipole chosen, although with dipole 3 some degree of synchrony was found in the formation of cycloadduct 5. The 1,3-DC between 1 and 3 was regioselective, being the cycloadduct 11 favoured against 9. The NMR chemical shift parameters (GIAO method) were also calculated for the reactives and cycloadducts. 相似文献
13.
The electronic mechanism for the gas-phase concerted 1,3-dipolar cycloaddition of diazomethane (CH2N2) to ethene (C2H4) is described through spin-coupled (SC) calculations at a sequence of geometries along the intrinsic reaction coordinate obtained at the MP2/6-31G(d) level of theory. It is shown that the bonding rearrangements occurring during the course of this reaction follow a heterolytic pattern, characterized by the movement of three well-identifiable orbital pairs, which are initially responsible for the pi bond in ethene and the C-N pi bond and one of the N-N pi bonds in diazomethane and are retained throughout the entire reaction path from reactants to product. Taken together with our previous SC study of the electronic mechanism of the 1,3-dipolar cycloaddition of fulminic acid (HCNO) to ethyne (C2H2) (Theor. Chim. Acc. 1998, 100, 222), the results of the present work suggest strongly that most gas-phase concerted 1,3-dipolar cycloaddition reactions can be expected to follow a heterolytic mechanism of this type, which does not involve an aromatic transition state. The more conventional aspects of the gas-phase concerted 1,3-dipolar cycloaddition of diazomethane to ethene, including optimized transition structure geometry, electronic activation energy, activation barrier corrected for zero-point energies, standard enthalpy, entropy and Gibbs free energy of activation, have been calculated at the HF/6-31G(d), B3LYP/6-31G(d), MP2/6-31G(d), MP2/6-31G(d,p), QCISD/6-31G(d) and CCD/6-31G(d) levels of theory. We also report the CCD/6-311++G(2d, 2p)//CCD/6-31G(d), MP4(SDTQ)/6-311++G(2d,2p)//CCD/6-31G(d) and CCSD(T)/6-311++G(2d, 2p)//CCD/6-31G(d) electronic activation energies. 相似文献
14.
Farid Moeinpour 《中国化学》2011,29(7):1429-1433
The regiochemistry of 1,3‐dipolar cycloaddition reactions of C,N‐diphenyl nitrone with some vinyl sulfox‐ imines as dipolarophile was investigated using density functional theory (DFT)‐based reactivity indexes and activation energy calculations at B3LYP/6‐31G(d) level of theory. Analysis of the geometries and bond orders (BOs) at the TS structures associated with the different reaction pathways shows that these 1,3‐dipolar cycloaddition reactions occur via an asynchronous concerted mechanism. Analysis of the local electrophilicity and nucleophilicity indexes permits an interpretation about the regioselectivity of these 1,3‐dipolar cycloaddition reactions. The theoretical results obtained in the work clearly predict the regiochemistry of the isolated cycloadducts and agree to experimental outcomes. 相似文献
15.
Di Valentin C Freccero M Gandolfi R Rastelli A 《The Journal of organic chemistry》2000,65(19):6112-6120
The problem of competition between concerted and stepwise diradical mechanisms in 1,3-dipolar cycloadditions was addressed by studying the reaction between nitrone and ethene with DFT (R(U)B3LYP/6-31G) and post HF methods. According to calculations this reaction should take place via the concerted cycloaddition path. The stepwise process is a viable but not competitive alternative. The R(U)B3LYP/6-31G study was extended to the reaction of the same 1, 3-dipole with cyclobutadiene and benzocyclobutadiene. The very reactive antiaromatic cyclobutadiene has an electronic structure that is particularly disposed to promote stepwise diradical pathways. Calculations suggest that its reaction with nitrone represents a borderline case in which the stepwise process can compete with the concerted one on similar footing. Attenuation of the antiaromatic character of the dipolarophile, i.e., on passing from cyclobutadiene to benzocyclobutadiene, causes the concerted 1,3-dipolar cycloaddition to become once again prevalent over the two-step path. Thus, our results suggest that, in 1,3-dipolar cycloadditions that involve normal dipolarophiles, the concerted path (Huisgen's mechanism) should clearly overwhelm its stepwise diradical (Firestone's mechanism) counterpart. 相似文献
16.
The molecular structure and conformational stability of allylisocyanate (CH2CHCH2NCO) molecule was studied using the ab initio and DFT methods. The geometries of possible conformers, C-gauche (δ=120°, θ=0°) (δ=C=C–C–N and θ=C–C–N=C) and C-cis N-trans (δ=0° and θ=180°) were optimized employing HF/6-31G*, MP2/6-31G* levels of theory of ab initio and BLYP, B3LYP, BPW91 and B3PW91 methods of DFT implementing the atomic basis set 6-311+G(d,p). The structural and physical parameters of the above conformers were discussed with the experimental and theoretical values of the related molecules, methylisocyanate and 3-fluoropropene. It has been found that the N=C=O bond angle is not linear as the experimental result for both the conformers and the theoretical bond angle is 173°. The rotational potential energy surfaces have been performed at the HF/6-31G*, and MP2/6-31G* levels of theory. The Fourier decomposition potentials were analysed at the HF/6-31G*, and MP2/6-31G* levels of theory. The HF/6-31G* level of theory predicted that the C-gauche conformer is more stable than the C-cis N-trans conformer by 0.41 kJ/mol, but the MP2 and DFT methods predicted the C-cis N-trans conformer is found to be more stable than the C-gauche conformer. The calculated chemical hardness value at the HF/6-31G* level of theory predicted the C-cis N-trans form is more stable than C-gauche form, whereas the chemical hardness value at the MP2/6-31G* level of theory favours the slight preference towards the C-gauge conformer. 相似文献
17.
Ab initio calculations predict that D3d symmetry of Si2F6 is more stable than D3h symmetry. The calculated potential barrier to internal rotation was 0.77, 0.73 and 0.78 kcal/mol using HF/6-31G*, B3LYP/6-31G* and MP2/6-31G* methods respectively, which was in good agreement with the experimental value between 0.51±0.10 and 0.73±0.14 kcal/mol. The optimized geometries, harmonic force fields, infrared intensities, Raman activities, and vibrational frequencies are reported for D3d symmetry of Si2F6 from HF/6-31G* and B3LYP/6-31G*. A normal coordinate analysis was carried out. The average error between the scaled DFT frequencies obtained from the B3LYP/6-31G* calculation and observed frequencies was 4.2 cm−1 and the average error between the scaled HF and observed frequencies was 2.2 cm−1. 相似文献
18.
Rajnish Moudgil Damanjit Kaur Rachita Vashisht Prasad V Bharatam 《Journal of Chemical Sciences》2000,112(6):623-629
Ab initio HF/6-31+G*, MP2/6-31+G*, B3LYP/6-31+G* level calculations have been performed on HSe-NH2 to estimate the Se-N rotational barriers and N-inversion barriers. Two conformers have been found withsyn andanti arrangement of the NH2 hydrogens with respect to Se-H bond. The N inversion barriers in selenamide are 1.65, 2.47, 1.93 kcal/mol and the Se-N rotational
barriers are 6.58, 6.56 and 6.12 kcal/mol respectively at HF/6-31+G*, MP2/6-31+G* and B3LYP/6-31+G* levels respectively. The
nN →Σ *Se-H negative hyperconjugation is found to be responsible for the higher rotational barriers. 相似文献
19.
M. S. Novikov A. F. Khlebnikov K. A. Khistyaev I. Magull 《Russian Chemical Bulletin》2008,57(5):1070-1079
Reaction of difluorocarbene with diarylmethanimines leads to the formation of gem-difluorinated NH-azomethine ylides, two types of competing transformations of which are found to be characteristic: a formal 1,2-H shift into N-(difluoromethyl)imines and 1,3-dipolar cycloaddition to electron-deficient multiple bonds. α,α,α-Trifluoroaceto-phenones are efficient dipolar traps for difluoro NH-ylides, the addition of which to the dipole proceeds regioselectively with the formation of 4-fluoro-2,5-dihydrooxazoles. According to the quantum-chemical calculations by the DFT B3LYP/6-31G* method, 1,3-dipolar cycloaddition of difluorinated NH-azomethine ylides to a C=O bond with the formation of 4-fluoro derivatives of oxazole has lower barrier of activation than the reaction, leading to another regioisomer; the formal 1,2-H shift in the ylide occurs intermolecularly with participation of an imine, a precursor of the ylide. 相似文献
20.
To explore the regio- and stereoselectivity in Diels–Alder reactions of vinylallenes with acrolein, a parent vinylallene/acrolein system and a methyl-substituted vinylallene/acrolein system were studied. Ab initio calculations were used to identify eight transition state structures for each of the two Diels–Alder reactions at various computational levels (RHF/6-31G(d), RHF/6-311G(2d), B3LYP/6-311G(2d), and MP2/6-311G(2d)). The relative energies of the endo and exo transition states along with the regioselectivity have been determined from these calculations. In the parent vinylallene/acrolein system, the endo s-cis transition structure is the preferred stereoselectivity at all levels of theory, however, there is no regioselectivity. In the methyl substituted vinylallene/acrolein system, the endo s-trans transition state tends to compete with the endo s-cis transition state at the RHF levels of theory and is 1 kcal/mol more stable at the B3LYP/6-311G(2d) level of theory. Also, in the methyl-substituted system, there is now a definite preference for one regioisomer over the other. Both Diels–Alder reaction systems are asynchronous with the methyl-substituted system being more pronounced. 相似文献