Cope Rearrangement in Bicyclo[5.1.0]octa-2,5-diene and its Mono- and Di-Hetero Analogues: A DFT Study

2017 ◽  
Vol 70 (6) ◽  
pp. 683
Author(s):  
Priya Yadav ◽  
Shilpa Yadav ◽  
Asha Gurjar ◽  
Raj K. Bansal
Keyword(s):  
Activation Energy ◽  
Gas Phase ◽  
Density Functional ◽  
Room Temperature ◽  
Transition States ◽  
Cope Rearrangement ◽  
Functional Theory ◽  
Concerted Mechanism ◽  
Free Activation Energy ◽  
Cope Rearrangements

The Cope rearrangements of bicyclo[5.1.0]octa-2,5-diene and its 4-hetero-(aza/oxa/phospha) and 4,8-dihetero analogues were investigated using density functional theory at the B3LYP/6–31+G* level in gas phase. The rearrangements of bicyclo[5.1.0]octa-2,5-diene and its symmetrical 4,8-dihetero analogues followed a concerted mechanism involving synchronous transition states. In other cases, although a concerted mechanism was observed, asynchronous transition states were involved. In the case of bicyclo[5.1.0]octa-2,5-diene, a degenerate Cope rearrangement was expected to occur at room temperature (25°C) due to a low free activation energy (ΔG‡ = 14.46 kcal mol–1). However, under similar conditions, the rearrangement of 4,8-dioxabicyclo[5.1.0]octa-2,5-diene was much slower (ΔG‡ = 23.85 kcal mol–1) and the 4,8-diaza- and diphospha analogues did not undergo Cope rearrangement. The Cope rearrangements of 4-phospha-, 8-aza-, 8-aza-4-oxa-, 8-aza-4-phospha-, and 8-oxa-4-phospha-bicyclo[5.1.0]octa-2,5-dienes were exergonic and were expected to occur spontaneously to form the corresponding products. In contrast, rearrangement of 8-oxabicyclo[5.1.0]octa-2,5-diene, though exergonic, was accompanied by a decrease in entropy, due to which Cope rearrangement would occur much more slowly and a mixture of both valence isomers would be formed. The Cope rearrangements of 4-aza-, 4-oxa-, 4-aza-8-oxa-, 8-phospha-, 4-aza-8-phospha-, 4-oxa-8-phospha-, and 4,8-diphospha-bicyclo[5.1.0]octa-2,5-dienes were endergonic; consequently either no Cope rearrangement would take place or it would occur sluggishly.

Temperature Dependence of Disproportionation–Combination Ratios for Alkyl Radicals in Liquid Methane

1971 ◽  
Vol 49 (17) ◽  
pp. 2861-2867 ◽  
Author(s):  
Hugh A. Gillis
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Gas Phase ◽  
Rate Constants ◽  
Room Temperature ◽  
Transition States ◽  
Alkyl Radicals ◽  
Liquid Methane ◽  
Ethyl Radicals

The ratios of rate constants for disproportionation to combination have been measured for ethyl radicals and for i-propyl radicals in liquid methane between −181 and −94 °C. The radicals were generated by γ-radiolysis of dilute methane solutions of ethylene-d4 or propylene-d6. The activation energy for combination was found to exceed that for disproportionation by 290 ± 30 cal mol−1 for ethyl radicals and by 255 ± 25 cal mol−1 for i-propyl radicals. In both cases the disproportionation—combination ratio in the liquid, extrapolated to room temperature, is greater than that in the gas phase by a factor of about 2.5. These results are interpreted as indicating that disproportionation and combination reactions proceed by way of different transition states.

DFT interpretations for cycloadditions of an electron deficient C-aryl-N-phenyl nitrone

2014 ◽  
Vol 13 (01) ◽  
pp. 1450007 ◽  
Author(s):  
Nivedita Acharjee
Keyword(s):  
Density Functional ◽  
Transition States ◽  
Density Functional Theory Calculations ◽  
Basis Set ◽  
Dipolar Cycloaddition ◽  
Functional Theory ◽  
Concerted Mechanism ◽  
Reaction Channels ◽  
Calculated Activation Energy ◽  
Calculated Activation

1,3-dipolar cycloaddition reactions of an electron deficient C-aryl-N-phenyl nitrone to benzylidene derivatives (with different electrophilicities) have been analyzed by density functional theory calculations. The transition states corresponding to the endo and exo approaches along the feasible regioisomeric reaction channels have been located for each cycloaddition. The reactions follow a concerted mechanism with asynchronous transition states. The asynchronicity along the regiochemical reaction modes depends on the β-carbon electrophilicities of the olefins. The regio and stereochemistries predicted from the calculated activation energy barriers (with solvent and higher basis set corrections) of the located transition states are in conformity with the experimental results. The local electrophilicities, softness matching indices and the interaction energies were then calculated to analyze how well these reactivity parameters can interpret the regioselectivities of such reactions. The electronic populations at the reactive sites computed from electrostatic potential-driven atomic charges provided correct and consistent predictions for each theoretical model contrary to the natural orbital based charges.

scholarly journals Theoretical study on the mechanism of reaction between 3-hydroxy-3-methyl-2-butanone and malononitrile catalyzed by lithium ethoxide

2008 ◽  
Vol 6 (2) ◽  
pp. 304-309 ◽  
Author(s):  
Qi-Shan Hu ◽  
Lai-Cai Li ◽  
Xin Wang
Keyword(s):  
Activation Energy ◽  
Vibration Analysis ◽  
Density Functional ◽  
Theoretical Study ◽  
Transition States ◽  
Functional Theory ◽  
Bond Forming ◽  
Uncatalyzed Reaction ◽  
Mechanism Of Reaction ◽  
Reaction Processes

AbstractThe The mechanism of reaction between 3-hydroxy-3-methyl-2-butanone and malononitrile for the synthesis of 2-dicyanomethylene-4, 5, 5-trimethyl-2,5-dihydrofuran-3-carbonitrile catalyzed by lithium ethoxide was investigated by density functional theory (DFT). The geometries and the frequencies of reactants, intermediates, transition states and products were calculated at the B3LYP/6-31G(d) level. The vibration analysis and the IRC analysis verified the authenticity of transition states. The reaction processes were confirmed by the changes of charge density at the bond-forming critical point. The results indicated that lithium ethoxide is an effective catalyst in the synthesis of 2-dicyanomethylene-4, 5, 5-trimethyl-2, 5-dihydrofuran-3-carbonitrile from malononi-trile and 3-hydroxy-3-methyl-2-butanone. The activation energy of the reaction with lithium ethoxide was 115.86 kJ·mol−1 less than the uncatalyzed reaction. The mechanism of the lithium ethoxide catalyzed reaction differed from the mechanism of the uncatalyzed reaction.

scholarly journals A density functional theory study on the mechanism of the allylpalladium-catalyzed dehydrogenation of aldehydes and cyclic ketones

2021 ◽  
Vol 46 ◽  
pp. 146867832110206
Author(s):  
Anan Haj Ichia Arisha
Keyword(s):  
Density Functional Theory ◽  
Gas Phase ◽  
Density Functional ◽  
Transition States ◽  
Density Functional Theory Calculations ◽  
Carbonyl Complex ◽  
Cyclic Ketones ◽  
Complex Catalyst ◽  
Functional Theory ◽  
Hydride Elimination

The results of density functional theory calculations at the APFD/SDD level are detailed herein in order to study the main steps in the α,β-dehydrogenation of aldehydes and cyclic ketones in the presence of an allylpalladium complex catalyst. The mechanism is believed to proceed via an allylpalladium enolate complex (A) in equilibrium with the carbon-bonded complex (B), followed by β-hydride elimination to yield the allylpalladium hydride coordinated to the α,β-unsaturated carbonyl (complex C). The optimized structures and detailed energy profiles of these intermediates and their corresponding transition states are presented herein. The results indicate that the intermediates and their transition states are more stable in THF solution than in the gas phase. In detail, the energy barriers for the two steps are found to be 25.22 and 11.13 kcal/mol, respectively, in THF, and 29.93 and 9.77 kcal/mol, respectively, in the gas phase.

Theoretical Investigation of the Kinetic Effect of the 1-Ethylpyridinium Trifluoroacetate Ionic Liquid in the Acceleration of Diels–Alder Reactions of Isoprene with Acrylic Acid and Acrylonitrile

2017 ◽  
Vol 42 (4) ◽  
pp. 361-371 ◽  
Author(s):  
Hafida Chemouri ◽  
Sidi Mohamed Mekelleche
Keyword(s):  
Ionic Liquid ◽  
Acrylic Acid ◽  
Gas Phase ◽  
Density Functional ◽  
Diels Alder ◽  
Intrinsic Reaction Coordinate ◽  
Functional Theory ◽  
Concerted Mechanism ◽  
Kinetics Of ◽  
Explicit Solvation

The mechanism, the regioselectivity, the stereoselectivity and the kinetics of Diels–Alder reactions of isoprene with acrylic acid and acrylonitrile have been studied, at the B3PW91/6-31G(d,p) level of theory, both in the gas phase and in the presence of organic [dichloromethane (DCM)] and ionic liquid [1-ethylpyridinium trifluoroacetate (EPTFA)] solvents. Intrinsic reaction coordinate calculations show that these reactions take place through an asynchronous concerted mechanism leading to the endo para cycloadducts as the major products in the gas phase and to the exo para cycloadducts as the major products both in organic and in ionic liquid solvents. The explicit solvation model involving the coordination of one molecule of the solvent with the dienophiles shows a considerable decrease of the activation energy when passing from DCM to EPTFA. The enhancement of these cycloaddition reactions can be explained by the strong hydrogen bonding created between the ion pair of the ionic liquid and the oxygen atom of the dienophile reagents. Moreover, density functional theory-based reactivity indices also show an increase of the reaction polarity and consequently of the reaction rate, when replacing DCM solvent by EPTFA solvent. The results obtained give evidence that the ionic liquid EPTFA is an excellent solvent for Diels–Alder reactions in comparison with conventional organic solvents.

scholarly journals NBO and NICS analysis of the allylic rearrangements (the Cope and 3-aza-Cope rearrangements) of hexa-1,5-diene and N-vinylprop-2-en-1-amine: A DFT study

2010 ◽  
Vol 8 (5) ◽  
pp. 1097-1104 ◽  
Author(s):  
Ehsan Zahedi ◽  
Safa Ali-Asgari ◽  
Vahid Keley
Keyword(s):  
Density Functional ◽  
Transition States ◽  
Nbo Analysis ◽  
Cope Rearrangement ◽  
Sigmatropic Rearrangements ◽  
Aromatic Character ◽  
Plane Component ◽  
Out Of Plane ◽  
Donor Acceptor ◽  
Cope Rearrangements

AbstractIn this work, ab initio density functional theory (DFT) calculations have been performed on the 3,3-sigmatropic rearrangements of hexa-1,5-diene (Cope) and N-vinylprop-2-en-1-amine (3-aza-Cope) in the gas phase. The barrier heights and heats of reactions calculated at the B3LYP/6-311G** level of theory were in good agreement with experimental data. Transition states optimized with B3LYP/6-311G** theory were used for calculating the nucleus independent chemical shift (NICS) and, a natural bond orbital (NBO) analysis was also performed at the same level of theory. Our results indicate that the aromaticities of the transition states are controlled by the out-of-plane component and that the chair-like transition state of the Cope rearrangement exhibits the strongest aromatic character. Analysis of donor-acceptor (bonding and anti-bonding) interactions of σ3–4 → π*1–2 suggests that the TS structure in the hexa-1,5-diene reaction (the Cope rearrangement) has more aromatic character than the N-vinylprop-2-en-1-amine reaction (the 3-aza-Cope rearrangement). The NBO results show that in the hexa-1,5-diene and N-vinylprop-2-en-1-amine rearrangements, activation energies are controlled by σ3–4 → π*1–2 and σ3–4 → π*1–2 resonance energies.

Intrinsic Stacking Interactions of Natural and Artificial Nucleobases

2019 ◽  
Author(s):  
Drew P. Harding ◽  
Laura J. Kingsley ◽  
Glen Spraggon ◽  
Steven Wheeler
Keyword(s):  
Gas Phase ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Molecular Descriptors ◽  
Stacking Interactions ◽  
Interaction Energies ◽  
Functional Theory ◽  
Binding Partner ◽  
Heavy Atoms ◽  
Wide Range

The intrinsic (gas-phase) stacking energies of natural and artificial nucleobases were explored using density functional theory (DFT) and correlated ab initio methods. Ranking the stacking strength of natural nucleobase dimers revealed a preference in binding partner similar to that seen from experiments, namely G > C > A > T > U. Decomposition of these interaction energies using symmetry-adapted perturbation theory (SAPT) showed that these dispersion dominated interactions are modulated by electrostatics. Artificial nucleobases showed a similar stacking preference for natural nucleobases and were also modulated by electrostatic interactions. A robust predictive multivariate model was developed that quantitively predicts the maximum stacking interaction between natural and a wide range of artificial nucleobases using molecular descriptors based on computed electrostatic potentials (ESPs) and the number of heavy atoms. This model should find utility in designing artificial nucleobase analogs that exhibit stacking interactions comparable to those of natural nucleobases. Further analysis of the descriptors in this model unveil the origin of superior stacking abilities of certain nucleobases, including cytosine and guanine.

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