Structure-energy relations, reaction mechanism, and disparity of progress of concerted reaction events

1985 ◽  
Vol 107 (1) ◽  
pp. 125-133 ◽  
Author(s):  
Ernest Grunwald
Keyword(s):  
Reaction Mechanism ◽  
Energy Relations ◽  
Concerted Reaction

The ozone–acetylene reaction: concerted or non-concerted reaction mechanism? A quantum chemical investigation

2001 ◽  
Vol 347 (1-3) ◽  
pp. 268-276 ◽  
Author(s):  
Dieter Cremer ◽  
Elfi Kraka ◽  
Ramon Crehuet ◽  
Josep Anglada ◽  
Jürgen Gräfenstein
Keyword(s):  
Reaction Mechanism ◽  
Quantum Chemical ◽  
Chemical Investigation ◽  
Quantum Chemical Investigation ◽  
Concerted Reaction

SOLVENT AND SUBSTITUENT EFFECTS ON THE INTRAMOLECULAR AMIDE HYDROLYSIS OF N-METHYLMALEAMIC ACID

2009 ◽  
Vol 08 (06) ◽  
pp. 1217-1226 ◽  
Author(s):  
JUN CAI ◽  
ZHIJIAN WU
Keyword(s):  
Reaction Mechanism ◽  
Gas Phase ◽  
Reaction Mechanisms ◽  
Substituent Effects ◽  
Phase Reaction ◽  
Gas Phase Reaction ◽  
Amide Hydrolysis ◽  
Reaction Barriers ◽  
Hydrolysis Of ◽  
Concerted Reaction

Intramolecular amide hydrolysis of N-methylmaleamic acid is revisited at the B3LYP/6-311G(2df, p)//B3LYP/6-31G(d, p) + ZVPE level, including solvent effects at the CPCM-B3LYP/6-311G(2df, p)//Onsager-B3LYP/6-31G(d, p) + ZPVE level. The concerted reaction mechanism is energetically favorable over stepwise reaction mechanisms in both the gas phase and solution. The calculated reaction barriers are significantly lower in solution than in the gas phase. In addition, it is concluded that the substituents of the four N-methylmaleamic acid derivatives considered herein have a significant effect on the gas-phase reaction barriers but a smaller, or little, effect on the barriers in solution.

scholarly journals Ab-Initio Computational Study : The Activation Energy Changes and Steric Effects In Peptide Synthesis Of Ac-AA-NH2 and Ac-AP-NH2

Molekul ◽  
2021 ◽  
Vol 16 (2) ◽  
pp. 137
Author(s):  
Indah Pratiwi ◽  
Bambang Cahyono ◽  
Parsaoran Siahaan
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Ab Initio ◽  
Peptide Synthesis ◽  
Reaction Mechanisms ◽  
Steric Effect ◽  
Computational Study ◽  
Computational Method ◽  
Side Chain ◽  
Concerted Reaction

Ab-Initio computational method can be used for simulating reaction mechanisms, such as concerted reaction mechanism on peptide synthesis. The concerted reaction is one of many possible pathways on how peptide can be synthesized. The purpose of this study are probing the concerted reaction mechanism and comparing the steric effect to the reaction, given by different side-chain of alanine (A) and proline (P). Two dipeptides formed from alanine and proline were computed at HF-SCF/6-31G** theory level: Ac-AA-NH2 and Ac-AP-NH2. The res.lts show the activation energy of Ac-AA-NH2  and Ac-AP-NH2 forming via concerted pathway are 167.541 kJ/mol and 161.044 kJ/mol, respectively. The steric difference in side-chain affects the dihedral angle of the structure, and also gives difference to the entropy value of reaction.

Study of trichloronitrosomethane: regioselective cycloadditions of 2-substituted-1,3-butadienes

1989 ◽  
Vol 67 (12) ◽  
pp. 2153-2161 ◽  
Author(s):  
Cheng-Tung Lin ◽  
Wen-Jei Hsu
Keyword(s):  
Electron Transfer ◽  
Reaction Mechanism ◽  
Transition State ◽  
Molecular Orbital ◽  
Kinetic Studies ◽  
Frontier Molecular Orbital ◽  
Cycloaddition Reactions ◽  
Orientation Preference ◽  
Straight Lines ◽  
Concerted Reaction

The regioselectivity of cycloaddition reactions of trichloronitrosomethane (1) with 2-alkyl (R = Me, Et, i-Pr, t-Bu, CF3, Bz, and Cl) and 2-aryl (Ar = Ph, 4-CH3OPh, 4-CH3Ph, 3-CH3Ph, and 4-ClPh) 1,3-butadienes is described. The orientation of cycloaddition is substituent dependent, producing 2,5-disubstituted (para) and 2,4-disubstituted (meta) 3,6-dihydro-1,2-oxazines from 2-alkyl- and 2-aryl-1,3-butadienes respectively. Increasing the bulk of the substituent from methyl to tert-butyl in 2-alkyl-1,3-butadienes increases the regioselectivity. Kinetic studies in various solvents indicate that plots of log km/kH vs. Hammett σ+ values give straight lines with the ρ values lying between −0.60 and −0.91 for the reactions with 2-aryl-1,3-butadienes. A concerted reaction mechanism is proposed and the orientation preference is consistent with frontier molecular orbital predictions for 2-alkyl-1,3-butadienes. In the reactions with 2-aryl-1,3-butadienes, a transition state leading to a spin-paired diradical, which then converts by partial electron transfer to zwitterionic structure, is proposed. Keywords: trichloronitrosomethane, 3,6-dihydro-1,2-oxazine, regioselectivity, [2 + 4] cycloaddition.

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