Perpendicular effects on transition states. 2. Energy profiles and reaction surfaces

1987 ◽  
Vol 52 (11) ◽  
pp. 2192-2195 ◽  
Author(s):  
Noam Agmon
Keyword(s):  
Transition States ◽  
Energy Profiles ◽  
Reaction Surfaces

A molecular mechanics study of conformational isomerism in 1- and 3-aryl hydantoins and 3-aryl-2-thiohydantoins

1991 ◽  
Vol 69 (12) ◽  
pp. 1957-1963 ◽  
Author(s):  
Lawrence D. Colebrook
Keyword(s):  
Force Field ◽  
Key Words ◽  
Molecular Mechanics ◽  
Internal Rotation ◽  
Transition States ◽  
Rotational Energy ◽  
Conformational Isomerism ◽  
Hindered Rotation ◽  
Energy Profiles ◽  
Conformational Preferences

Energy profiles for internal rotation about the C—N pivot bond in a series of 1- and 3-aryl hydantoins and 3-aryl-2-thiohydantoins have been computed using the MMX molecular mechanics force field. Rotational ground and transition states have been identified and their energies calculated. Conformational preferences of diastereomeric rotamers have been investigated. Computed rotational energy barriers generally are within ± 2 kcal/mol of the experimentally determined values. Key words: conformational isomerism, hindered rotation, hydantoins, thiohydantoins, molecular mechanics.

scholarly journals The Role of Homoaromaticity in the Tropylium-Catalyzed Carboxylic Acid O-H Insertion with Diazoesters

2022 ◽  
Author(s):  
Anakuthil Anoop ◽  
Venkataraman Ganesh
Keyword(s):  
Carboxylic Acid ◽  
Dft Calculations ◽  
Computational Model ◽  
Computational Methods ◽  
Transition States ◽  
Energy Profiles ◽  
Clear Insight ◽  
Hydroxy Esters ◽  
Insight Into

The tropylium catalyzed carboxylic acid O-H insertion with diazoesters providing α-hydroxy esters was reported recently through an activated carbene as the key intermediate. We report a revised mechanism involving a unique homoaromatic intermediate with the tropylium ion and the diazoester based on the DFT calculations. Our computational model provides a clear insight into the binding of the tropylium ion with the diazoester providing the homoaromatic intermediate. The reaction profiles of four different pathways were compared. The energies of the intermediates and the transition states are reported at B97-D3(SMD)/def2TZVP//B97-D3/def2TZVP (in dichloromethane). The energy profiles were compared across a few computational methods to study the sensitivity of our model across methods.

Theoretical Computations on the Pyrolysis of Alkyl (dithio)acetates

2020 ◽  
Vol 17 (3) ◽  
pp. 224-233
Author(s):  
Xun Zhu ◽  
Chen Jian ◽  
Xiuqin Zhou ◽  
Abdullah M. Asiri ◽  
Khalid A. Alamry ◽  
...  
Keyword(s):  
Transition States ◽  
Membered Ring ◽  
Pyrolysis Process ◽  
Alkyl Esters ◽  
Charge Distributions ◽  
Theoretical Analyses

The pyrolysis of methyl alkyl esters I to III and dithioesters IV to VI were theoretically calculated. All possible pyrolysis paths were considered. Both esters and dithioesters presented three potential paths via six-, four- and five-membered ring transition states, respectively. The calculation processes were calculated using MP2/6-31G(d) set. In-depth theoretical analyses were also presented, including NBO related analyses, synchronicities, and charge distributions, to reveal the detailed pyrolysis process.

Sterically Crowded Heterocycles. X. A New Mechanistic Approach to the Ferricyanide Oxidation of 4,6'-Disubstituted 1-(Pyridin-2'-yl)-2,6-diphenylpyridinium Salts

1999 ◽  
Vol 64 (8) ◽  
pp. 1274-1294 ◽  
Author(s):  
Radek Pohl ◽  
Stanislav Böhm ◽  
Josef Kuthan
Keyword(s):  
Transition States ◽  
Oxidative Transformation ◽  
Steric Interactions ◽  
Radical Intermediates ◽  
Mechanistic Approach

The oxidations of the title perchlorates, bearing the sterically diverse 6'-substituents (H, Me, Et, i-Pr, n-Bu, t-Bu and Ph) in two series with the same 4-substituents (Ph and t-Bu) lead to pairs of isomeric 3',5-disubstituted (Z)-1'-phenyl-3'-(2-phenylimidazo[1,2-a]pyridin-3-yl)prop-2'- en-1'-ones and 3,6'-disubstituted [5-phenyl-1-(6'-pyridin-2'-yl)-1H-pyrrol-2-yl](phenyl)methanones except where the both variable substituents are t-Bu and then only pyrrolic product is formed. Considering steric interactions of the substituents in some intermediate and/or transition states a multistep mechanism for the oxidative transformation is proposed and supported by model PM3-PECI calculations of some radical intermediates.

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