ChemInform Abstract: RATES, ACTIVATION PARAMETERS, AND ENTHALPIES OF TRANSFER OF TRANSITION STATES FOR THE REACTION OF IMIDAZOLE WITH AROMATIC SULPHONYL CHLORIDES IN METHANOL AND ACETONITRILE

1973 ◽  
Vol 4 (29) ◽  
pp. no-no
Author(s):  
OTTO ROGNE
Keyword(s):  
Transition States ◽  
Activation Parameters ◽  
Enthalpies Of Transfer

[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.

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.

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.

Enthalpies of transfer of transition states in the Menshutkin reaction from a polar protic to a dipolar aprotic solvent

1971 ◽  
Vol 36 (13) ◽  
pp. 1792-1795 ◽  
Author(s):  
Paul Haberfield ◽  
Abraham Nudelman ◽  
Allen Bloom ◽  
Richard Romm ◽  
Henry Ginsberg
Keyword(s):  
Aprotic Solvent ◽  
Transition States ◽  
Dipolar Aprotic Solvent ◽  
Enthalpies Of Transfer ◽  
Menshutkin Reaction

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.

scholarly journals A Computational Study of 2-(chloromethyl)oxirane Ring Opening by Bromide and Acetate Anions Considering Electrophilic Activation with Cations of Alkali Metals

2019 ◽  
Vol 92 (3) ◽  
pp. 357-367 ◽  
Author(s):  
Kseniia Yutilova ◽  
Yuliia Bespal’ko ◽  
Elena Shved
Keyword(s):  
Alkali Metal ◽  
Metal Cation ◽  
Ring Opening ◽  
Density Functional ◽  
Alkali Metals ◽  
Computational Study ◽  
Alkali Metal Cation ◽  
Transition States ◽  
Activation Parameters ◽  
Electrophilic Activation

Ring opening of 2-(chloromethyl)oxirane via the nucleophilic substitution with bromide and acetate anions was investigated using density functional theory (DFT) calculations. It was shown that the geometry of the transition states and the activation parameters of the reactions correspond to those of SN2-like mechanism. The nature of localized transition states was analyzed using More O’Ferrall – Jencks plots. The quantum chemical simulations of the potential energy surface for the ring-opening reaction of oxirane by nucleophiles confirmed the theoretical assumptions about the favored path of interactions, which is a backside α-attack of nucleophile. The effect of alkali metal cation (Li+, Na+, K+) on that path was estimated. It was found that the electrophilic activation with alkali metal cation is more pronounced in the reaction of 2-(chloromethyl)oxirane with dissociated ions, than with ionic pairs.

Isotope effects in nucleophilic substitution reactions. IV. The effect of changing a substituent at the α carbon on the structure of SN2 transition states

1982 ◽  
Vol 60 (19) ◽  
pp. 2500-2520 ◽  
Author(s):  
Kenneth Charles Westaway ◽  
Zbigniew Waszczylo
Keyword(s):  
Nucleophilic Substitution ◽  
Isotope Effects ◽  
Transition States ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Kinetic Isotope Effects ◽  
Substitution Reactions ◽  
Nucleophilic Substitution Reactions ◽  
Kinetic Isotope ◽  
Benzyl Chlorides

Kinetic studies, secondary α-deuterium kinetic isotope effects, primary chlorine kinetic isotope effects (1), Hammett ρ values determined by changing the substituent in the nucleophile, and activation parameters have been used to determine the detailed (relative) structures of the transition states for the SN2 reactions between para-substituted benzyl chlorides and thiophenoxide ion. A rationale for the U-shaped Hammett ρ plots observed when para-substituted benzyl compounds react with negatively charged nucleophiles is also presented.

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