Understanding the mechanism of the decomposition reaction of nitroethyl benzoate through the Molecular Electron Density Theory

A molecular electron density theory study on the Chichibabin reaction: The origin of regioselectivity

A Molecular Electron Density Theory (MEDT) study was performed on the nucleophilic amination of pyridine and benzene to elucidate the observed regioselectivity in the Chichibabin reaction. For this purpose, three possible reaction paths were considered between NaNH₂ and the 2-, 3- and 4-positions of pyridine. The reaction of NaNH₂ and benzene was also investigated. The results indicated that in each reaction, the first step involves the nucleophilic attack of the NH₂‾ ion toward the aromatic system to produce an anionic intermediate. The second step, proceeds via hydride elimination of the anionic intermediate to produce the corresponding aromatic amine. This step is more favourable both kinetically and thermodynamically for the reaction at the 2-position of pyridine relative to the 4-position. In contrast to the Parr functions analysis which indicates that the 4-position is activated more electrophilically in pyridine, the PES analysis reveals that the 2-position attack with the NH₂‾ ion is more favourable both thermodynamically and kinetically. The results for the reaction of sodium amide and benzene indicated that this reaction is not feasible due to the high activation barriers. In consistent with the experimental results, the ELF analysis indicated that in the first step of the reaction between pyridine and sodium amide, the formation of the C2-N bond takes place via a pseudoradical coupling between the C2 carbon atom of pyridine and the N atom of NaNH₂. These variations occur in the second-half of the first step of the reaction. NCI analysis on the reaction revealed that the more attractive forces between the fragments, make the transition states for the 2-position attack more stable relative to the others. Thus, the NCI analysis can satisfactorily describe the observed regioselectivity in the Chichibabin reaction.

Chemoselective Oxidation of Isoxazolidines with Ruthenium Tetroxide: A Successful Intertwining of Combined Theoretical and Experimental Data

The direct oxidation reaction of isoxazolidines plays an important role in organic chemistry, leading to the synthesis of biologically active compounds. In this paper, we report a computational mechanistic study of RuO₄-catalyzed oxidation of differently N-substituted isoxazolidines 1a–c. Attention was focused on the endo/exo oxidation selectivity. For all the investigated compounds, the exo attack is preferred to the endo one, showing exo percentages growing in parallel with the stability order of transient carbocations found along the reaction pathway. The study has been supported by experimental data that nicely confirm the modeling results.

On the Mechanism of the Synthesis of Nitrofunctionalised Δ2-Pyrazolines via [3+2] Cycloaddition Reactions between α-EWG-Activated Nitroethenes and Nitrylimine TAC Systems

We investigated the reactivity of different substituted nitrylimine-type three atom components (TACs) in [3+2] cycloaddition (32CAs) reactions with electrophilically activated nitroethenes within molecular electron density theory (MEDT). In parallel research, the molecular mechanism of the considered transformation was examined through analysis of all possible reaction channels and full optimization of all critical structures. In particular, the existence of zwitterionic intermediates on reaction paths was verified. On the basis of the bonding evolution theory (BET), the mechanism of the 32CA reaction between C,N-diphenylnitrylimine and (E)-2-phenyl-1-cyano-1-nitroethene should be treated as a one-step two-stage mechanism.

The Molecular Mechanism of the Formation of Four-Membered Cyclic Nitronates and Their Retro (3 + 2) Cycloaddition: A DFT Mechanistic Study

In the present work, the formation of the four-membered cyclic nitronates and the retro (3 + 2) cycloaddition (retro-32CA) reaction of the 4H-[1,2]oxazete 2-oxide were studied using the density functional theory method at the MPWB1K/6-311G(d,p) theoretical level. The electronic structure of 3-tert-butyl-4,4-dimethyl-1,2-dinitro-pent-2-ene was known through electron localization function analysis, natural population analysis, and molecular electrostatic potential analysis. The formation of 4,4-di-tert-butyl-3-nitromethyl-4H-[1,2]oxazete 2-oxide proceeds through a one-step mechanism. The mechanism of the retro-32CA leading to di-tert-butyl ketone and nitrile oxide derivative should be described as an asynchronous two-stage one-step process. The bonding evolution theory study was carried out to clarify the mechanisms of the formation of 4H-[1,2]oxazete 2-oxide and their retro-32CA.

Understanding the Molecular Mechanism of the Rearrangement of Internal Nitronic Ester into Nitronorbornene in Light of the MEDT Study

The characterization of the structure of nitronic esters and their rearrangement into nitronorbornene reactions has been analyzed within the Molecular Electron Density Theory (MEDT) using Density Functional Theory (DFT) calculations at the B3LYP/6-31G(d) computational level. Quantum-chemical calculations indicate that this rearrangement takes place according to a one-step mechanism. The sequential bonding changes received from the Bonding Evolution Theory (BET) analysis of the rearrangement of internal nitronic ester to nitronorbornene allowed us to distinguish seven different phases. This fact clearly contradicts the formerly-proposed concerted pericyclic mechanism.