The activation parameters in thermolysis of norbornyl acetates and their significance for reaction mechanisms with cyclic transition states.

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

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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

Chemischer Informationsdienst ◽

10.1002/chin.197329140 ◽

1973 ◽

Vol 4 (29) ◽

pp. no-no

Author(s):

OTTO ROGNE

Keyword(s):

Transition States ◽

Activation Parameters ◽

Enthalpies Of Transfer

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

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc20021517 ◽

2002 ◽

Vol 67 (10) ◽

pp. 1517-1532 ◽

Cited By ~ 5

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.

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Enzyme action: The delineation of novel strategies based on reaction mechanisms and transition states

Pure and Applied Chemistry ◽

10.1351/pac199264081147 ◽

1992 ◽

Vol 64 (8) ◽

pp. 1147-1151 ◽

Cited By ~ 2

Author(s):

D. Ranganathan ◽

F. Farooqui ◽

R. Rathi ◽

S. Saini ◽

N. Vaish ◽

...

Keyword(s):

Reaction Mechanisms ◽

Transition States ◽

Enzyme Action

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

Journal of Theoretical and Computational Chemistry ◽

10.1142/s0219633614500710 ◽

2014 ◽

Vol 13 (08) ◽

pp. 1450071 ◽

Cited By ~ 1

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.

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