Acyclic and cyclic nitrone cycloadditions to 1-cinnamoyl-1-piperidine: A DFT study

2014 ◽  
Vol 13 (08) ◽  
pp. 1450071 ◽  
Author(s):  
Nivedita Acharjee
Keyword(s):  
Transition States ◽  
Activation Parameters ◽  
Interaction Energies ◽  
Reactivity Indices ◽  
Chemical Potentials ◽  
Experimental Findings ◽  
Electronic Chemical ◽  
Wiberg Bond Indices ◽  
Electron Demand ◽  
Trajectory Simulations

DFT studies have been carried out for the cycloaddition reactions of a cyclic nitrone, 1-pyrroline-1-oxide and an acyclic nitrone, C,N-diphenyl nitrone to an unsymmetrically disubstituted dipolarophile, 1-cinnamoyl-1-piperidine. These reactions proved to be opposite to each other with respect to the electron demand character predicted by the electronic chemical potentials, electrophilicities and charge transfer at the transition states. The regio- and stereoselectivities have been predicted from DFT based reactivity indices, interaction energy calculations using a perturbative orbital independent theoretical model and the activation parameters of the located transition states. Two different concepts have been used for the evaluation of interaction energies. The selectivities were found to be in conformity with the experimental findings. The time gaps between the formations of C – C and C – O bonds were evaluated from single trajectory simulations. The asynchronicity of bond formation process was analyzed from the wiberg bond indices, atom–atom overlap weighted NAO bond orders and the calculated asymmetry indices of the transition states.

[3,3] Sigmatropic Rearrangement of Some Fluorinated 1,5-Hexadienes

2002 ◽  
Vol 67 (10) ◽  
pp. 1517-1532 ◽  
Author(s):  
William R. Dolbier ◽  
Keith W. Palmer ◽  
Feng Tian ◽  
Piotr Fiedorow ◽  
Andrzej Zaganiaczyk ◽  
...  
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Transition States ◽  
Activation Parameters ◽  
Sigmatropic Rearrangement ◽  
Semiempirical Methods ◽  
Cope Rearrangement ◽  
Computational Studies ◽  
Stepwise Mechanism ◽  
Radical Intermediates

Fluorine atoms incorporated into 1,5-hexadiene molecule should influence the kinetic as well as the thermodynamic parameters of [3,3] sigmatropic rearrangement (Cope rearrangement). Within few decades is has been documented that this transformation proceeds in a concerted manner, rather than stepwise with some radical intermediates involved. Few new terminally fluorinated 1,5-hexadienes (compounds 3, 5A, 7, 9 and 5B) have been synthesized. The activation parameters of rearrangement have been determined and compared with those known for hydrocarbon analogues. While systems developing chair-like transition states (compounds 3 and 5) showed close similarity with hydrocarbon analogues (compound 1), those developing boat-like transition states (compounds 7, 9 and 5B) may proceed through radical stepwise mechanism. Computational studies of the transition states were carried out, showing that only ab initio methods (MP2 and especially DFT) can give approximate correlation with experimental data, whereas in the case of hydrocarbon analogues even simple semiempirical methods (AM1) were reliable enough to reproduce experimental results.

scholarly journals Mechanistic Aspects of Ligand Substitution on the Cis-Diaqua-Chloro-Tris(Dimethyl Sulfoxide)Ruthenium(II) Complex by Some Sulfur-Containing Bioactive Ligands in Aqueous Medium

2018 ◽  
Vol 43 (3-4) ◽  
pp. 274-285
Author(s):  
Animesh Chattopadhyay ◽  
Anwesha Dey ◽  
Parnajyoti Karmakar ◽  
Sumon Ray ◽  
Debabrata Nandi ◽  
...  
Keyword(s):  
Water Molecule ◽  
Dimethyl Sulfoxide ◽  
Aqueous Medium ◽  
Activation Parameters ◽  
Outer Sphere ◽  
Ring Closure ◽  
Bioactive Ligands ◽  
Experimental Findings ◽  
Job's Method ◽  
Sulfur Containing

The synthesis and interactions of the cis-diaqua-chloro-tris(dimethyl sulfoxide)ruthenium(II) complex with selected sulfur-containing ligands such as 2-thiouracil, glutathione and L-cysteine have been studied by UV-Vis spectrophotometry in aqueous medium at pH 4.5. From experimental data it is clear that all three reactions proceed via two steps: the first one being a rate-limiting ligand-dependent replacement of one water molecule, followed by a ligand-independent ring closure step with the expulsion of the second water molecule. The substituted products have been characterised by Job's method, FTIR spectroscopy and electrospray ionisation mass spectrometry. Activation parameters (Δ H≠ and Δ S≠) and thermodynamic parameters (Δ H0 and Δ S0, from the temperature dependence of the outer-sphere association equilibrium constant) are presented. Consistent with the experimental findings, an associative interchange mechanism is proposed.

Substituent and solvent effects on the reaction between 2,6-Di-t-butyl-α-(3,5-di-t-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)-p-tolyloxyl (galvinoxyl) and phenols

1978 ◽  
Vol 31 (6) ◽  
pp. 1201 ◽  
Author(s):  
N Nishimura ◽  
K Okahashi ◽  
T Yukutomi ◽  
A Fujiwara ◽  
S Kubo
Keyword(s):  
Carbon Tetrachloride ◽  
Binary Mixtures ◽  
Solvent Effects ◽  
Rate Constants ◽  
Isotope Effects ◽  
Mixed Solvents ◽  
Transition States ◽  
Activation Parameters ◽  
Substituted Phenols ◽  
Kinetic Behaviour

Rate constants and associated activation parameters for the reaction of galvinoxyl with substituted phenols were obtained in carbon tetrachloride and in cyclohexane-dioxan binary mixtures. Substantial isotope effects were observed for O-deuterated phenols. The rate constants are correlated with σ+ values. These findings are discussed by considering the polar contribution of substituents to the stabilization of the transition states. In the mixed solvents, the kinetic behaviour is well expressed by the equations which are based on the theory of Kondo and Tokura.

Kinetic and thermodynamic study of Os(VIII) catalysed oxidation of glycine by ferrate(VI) in alkaline medium

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Main Product ◽  
Activation Parameters ◽  
Basic Medium ◽  
First Order ◽  
Catalysed Oxidation ◽  
Rate Of Reaction ◽  
Different Temperatures ◽  
Experimental Findings ◽  
Kinetic And Thermodynamic Study ◽  
By Products

Kinetic and thermodynamic investigation on Os(VIII) catalysed oxidation of glycine by ferrate(VI) has been done in basic medium and in the temperature range 30– 450C. Rate of oxidation increases with increase in [FeO4]2- and [Os(VI)] and shows first order dependence. Rate of oxidation also increases with the increase in [S] but order is fractional. The rate decreases with an increase in pH. Rate of reaction is independent of [KCl], [KNO3] and change in ionic strength. The values of rate constant observed at four different temperatures were used to calculate the activation parameters. The energy of activation (ΔE*) of the reaction at pH 11 and temperature 350C was found to be 49.56 kJmol-1. [OsO4(H2O)2] and [FeO42−] are proposed to be the reactive species of Os(VIII) and Fe(VI) respectively in the present investigation. Formaldehyde is found to be main product of the reaction along with carbon dioxide and ammonia as by products. On the basis of experimental findings, a suitable mechanism consistent with the observed kinetics is proposed and a rate law has been derived on the basis of obtained data.

Ab Initio Study of Solvent Effects on Rate of 1,3-Dipolar Cycloadditions of Benzonitrile Oxide and Various Dipolarophiles

2003 ◽  
Vol 2003 (2) ◽  
pp. 91-95 ◽  
Author(s):  
E. Rajaeian ◽  
M. Monajjemi ◽  
M.R. Gholami
Keyword(s):  
Hydrogen Bonding ◽  
Oxygen Atom ◽  
Water Molecule ◽  
Ab Initio ◽  
Solvent Effects ◽  
Transition States ◽  
Molecular Orbital Calculations ◽  
Interaction Energies ◽  
Ab Initio Study ◽  
Dipolar Cycloadditions

Ab initio molecular orbital calculations have been used to investigate the structures and the transition states of 1,3-dipolar cycloadditions between benzonitrile oxide with ethylene, cyclopentene, acrylonitrile and tetracyanoethylene in heptane and water: calculations reveal enhanced hydrogen bonding of a water molecule to the transition states for the cycloaddition 1,3-dipolar of reaction of benzonitrile oxide with cyclopentene, the optimal interaction energies being 0.7 kcal/mol more favourable for hydrogen bonding to the oxygen atom in the transition states than for the reactants.

Studies of azo and azoxy dyestuffs. Part 18. Kinetics and mechanism of the hydrolysis of 3- and 4-(p′-methoxyphenylazo)pyridines in aqueous sulfuric acid media

1986 ◽  
Vol 64 (11) ◽  
pp. 2115-2126 ◽  
Author(s):  
Erwin Buncel ◽  
Ikenna Onyido
Keyword(s):  
Sulfuric Acid ◽  
Transition States ◽  
Activation Parameters ◽  
Nucleophilic Attack ◽  
Acid Solutions ◽  
Acid Media ◽  
Charge Delocalization ◽  
Leaving Group ◽  
The Difference ◽  
Hydrolysis Of

The kinetics of hydrolysis of 4-(p′-methoxyphenylazo)pyridine, 1, and its 3-isomer, 2, have been studied in moderately concentrated sulfuric acid media at 25 °C. In all the acid solutions investigated, 1 reacted faster than 2; rate differences between the two compounds varied from ca. 1000-fold in the dilute region of acidity to ca. 250-fold in the more concentrated acid solutions. The observed first-order rate constants, kψ, for both substrates exhibit a maximum, at ca. 42% H2SO4 and 47% H2SO4 for 1 and 2 respectively. Activation parameters have also been determined. The pKa values for the second protonation equilibria of 1 and 2 have been evaluated and structures of the diprotonated species are discussed. Hydrolysis is shown to occur from the diprotonated substrates and two main mechanisms are operative. The first is an A-2 type mechanism, which involves rate-limiting attack of H2O on the aryl carbon center giving delocalized transition states and intermediates in which the pyridinium and azonium functions are involved in charge delocalization. Subsequent transfer of a proton and detachment of the leaving group are fast processes. In the second A-SE2 type mechanism, nucleophilic attack and transfer of the proton are fast steps preceding the slow general acid catalyzed separation of the leaving group. The difference in reactivity of the two compounds is attributed to differences in extent of charge delocalization in the transition states of the reactions: for 1 both the pyridinium and protonated azonium functions are involved whereas for 2 only the azonium function participates in charge delocalization.

Addition of arenesulphenyl chlorides to 2-methylenebicyclo[2.2.1]hept-5-ene: effect of increasing electron demand upon the rate and product determining transition states

1980 ◽  
Vol 58 (10) ◽  
pp. 1021-1029 ◽  
Author(s):  
Dennis G. Garratt ◽  
Pierre L. Beaulieu ◽  
Veronique M. Morisset
Keyword(s):  
Double Bond ◽  
Chloride Solution ◽  
Methylene Chloride ◽  
Transition States ◽  
Exocyclic Double Bond ◽  
Electrophilic Attack ◽  
Methylene Chloride Solution ◽  
Major Species ◽  
Electron Demand

The rates and products of addition of a series of sixteen arenesulphenyl chlorides to 2-methylenebicyclo[2.2.1]hept-5-ene, 7, and the E, Z isomeric 2-ethylidenebicyclo[2.2.1]hept-5-enes, 8 and 9, have been determined in methylene chloride solution. The major species from attack on 7 is always endo-3-arylthio-1-chloromethyltricyclo[2.2.1.02,6]heptane, the product of exo attack upon the endocyclic double bond with homoallylic participation of the exocyclic π system. No evidence was found for initial electrophilic attack upon the exocyclic double bond.

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