Search results for "Exergonic reaction"
showing 10 items of 12 documents
A DFT study on the chiral synthesis of R-phenylacetyl carbinol within the quantum chemical cluster approach
2017
Abstract The reaction pathway leading to R-phenylacetyl carbinol within the quantum chemical cluster approach is addressed by means of density functional theory (DFT) calculations. The study includes calculation of Fukui functions, activation free energies, and potential energy surface scans, both in gas and solution phase. The protonation states of the nitrogen atoms of the pyrimidine moiety are determined. The reaction appears to be slightly exergonic (ΔG 0 = −5.6 and −4.0 kcal/mol for gas and solution phase, respectively) following a concerted synchronous mechanism having activation free energy barriers of 16.2 and 13.3 kcal/mol, in gas phase and solution phase, respectively.
Free energy profiles for two ubiquitous damaging agents: methylation and hydroxylation of guanine in B-DNA
2017
International audience; DNA methylation and hydroxylation are two ubiquitous reactions in DNA damage induction, yet insights are scarce concerning the free energy of activation within B-DNA. We resort to multiscale simulations to investigate the attack of a hydroxyl radical and of the primary diazonium onto a guanine embedded in a solvated dodecamer. Reaction free energy profiles characterize two strongly exergonic processes, yet allow unprecedented quantification of the barrier towards this damage reaction, not higher than 6 kcal mol−1 and sometimes inexistent, and of the exergonicities. In the case of the [G(C8)-OH]˙ intermediate, we challenge the functional dependence of such simulations…
A molecular electron density theory study of the insertion of CO into frustrated Lewis pair boron-amidines: a [4 + 1] cycloaddition reaction
2019
The insertion of CO into hydrogenated boron-amidine 1 yielding five-membered diazaborolone (5DAB) 3 has been studied within the molecular electron density theory (MEDT) at the DFT ωB97X-D/6-311G(d,p) level. This is a domino process comprised of two consecutive reactions: (i) the dehydrogenation of 1 yielding the frustrated Lewis pair (FLP) boron-amidine 4, which quickly equilibrates with four-membered diazaborolone (4DAB) 2; and (ii) the addition of CO into FLP 4, yielding the final 5DAB 3. Analysis of the Gibbs free energies indicates that the extrusion of H2 demands a high ΔG≠ of 28.6 kcal·mol-1, being endergonic by 6.7 kcal·mol-1. The subsequent addition of CO into FLP 4 presents a low Δ…
Unveiling the Intramolecular Ionic Diels–Alder Reactions within Molecular Electron Density Theory
2021
The intramolecular ionic Diels–Alder (IIDA) reactions of two dieniminiums were studied within the Molecular Electron Density Theory (MEDT) at the ωB97XD/6-311G(d,p) computational level. Topological analysis of the electron localization function (ELF) of dieniminiums showed that their electronic structures can been seen as the sum of those of butadiene and ethaniminium. The superelectrophilic character of dieniminiums accounts for the high intramolecular global electron density transfer taking place from the diene framework to the iminium one at the transition state structures (TSs) of these IIDA reactions, which are classified as the forward electro density flux. The activation enthalpy ass…
Synthesis, molecular structure and stability of fused bicyclic Δ4-1,2,4-oxadiazoline Pt(II) complexes
2015
Abstract The reaction of trans -[PtCl 2 (NCR) 2 ] (R 1 = CH 2 CO 2 Me ( 1a ), R 2 = CH 2 Cl ( 1b )) with pyrroline N -oxide − O + N CHCH 2 CH 2 C Me 2 ( 4 ), at room temperature for 15 min, furnishes via [3+2] cycloaddition the fused bicyclic Δ 4 -1,2,4-oxadiazoline Pt(II) complexes trans- [PtCl 2 { N C(R)O N C(H)CH 2 CH 2 C Me 2 } 2 ] (R 1 = CH 2 CO 2 Me ( 5a ), R 2 = CH 2 Cl ( 5b )). Compounds 5a and 5b were refluxed in CH 2 Cl 2 for 1 week to afford the derived ketoimine Pt(II) complexes trans- [PtCl 2 {N(C( O)(R)) C CH 2 CH 2 C(Me 2 ) N H} 2 ] (R 1 = CH 2 CO 2 Me ( 6a ), R 2 = CH 2 Cl ( 6b )), respectively, as a result of the N–O bond cleavage of the oxadiazoline ring in 5 . The c…
Understanding the domino reaction between 3-chloroindoles and methyl coumalate yielding carbazoles. A DFT study.
2014
The molecular mechanism of the reaction between N-methyl-3-chloroindole and methyl coumalate yielding carbazole has been studied using DFT methods at the MPWB1K/6-311G(d,p) level in toluene. This reaction is a domino process that comprises three consecutive reactions: (i) a polar Diels-Alder (P-DA) reaction between indole and methyl coumalate yielding two stereoisomeric [2 + 4] cycloadducts (CAs); (ii) the elimination of HCl from these CAs affording two stereoisomeric intermediates; and (iii) the extrusion of CO2 in these intermediates, finally yielding the carbazole. This P-DA reaction proceeds in a completely regioselective and slightly exo selective fashion. In spite of the highly polar …
Strain Release Chemistry of Photogenerated Small‐Ring Intermediates
2021
Abstract Photochemical processes, such as isomerizations and cycloadditions, have proven to be very useful in the construction of highly strained molecular frameworks. Photoinduced ring strain enables subsequent exergonic reactions which do not require the input of additional chemical energy and provides a variety of attractive synthetic options leading to complex structures. This review covers the progress achieved in the application of sequences combining excitation by ultraviolet light to form strained intermediates, which are further transformed to lower energy products in strain‐release reactions. As ring strain is considerable in small ring systems, photogenerated three‐ and four‐memb…
N-doped carbon networks: alternative materials tracing new routes for activating molecular hydrogen.
2014
The fragmentation of molecular hydrogen on N-doped carbon networks was investigated by using molecular (polyaromatic macrocycles) as well as truncated and periodic (carbon nanotubes) models. The computational study was focused on the ergonicity analysis of the reaction and on the properties of the transition states involved when constellations of three or four pyridinic nitrogen atom defects are present in the carbon network. Calculations show that whenever N-defects are embedded in species characterized by large conjugated π-systems, either in polyaromatic macrocycles or carbon nanotubes, the corresponding H2 bond cleavage is largely exergonic. The fragmentation Gibbs free energy is affect…
The Participation of 3,3,3-Trichloro-1-nitroprop-1-ene in the [3 + 2] Cycloaddition Reaction with Selected Nitrile N-Oxides in the Light of the Exper…
2021
The regioselective zw-type [3 + 2] cycloaddition (32CA) reactions of a series of aryl-substituted nitrile N-oxides (NOs) with trichloronitropropene (TNP) have been both experimentally and theoretically studied within the Molecular Electron Density Theory (MEDT). Zwitterionic NOs behave as moderate nucleophiles while TNP acts as a very strong electrophile in these polar 32CA reactions of forward electron density flux, which present moderate activation Gibbs free energies of 22.8–25.6 kcal·mol−1 and an exergonic character of 28.4 kcal·mol−1 that makes them irreversible and kinetically controlled. The most favorable reaction is that involving the most nucleophilic MeO-substituted NO. Despite P…
Unraveling the kinetics and molecular mechanism of gas phase pyrolysis of cubane to [8]annulene
2020
The kinetic and electron density flows are studied theoretically for the gas phase pyrolysis of cubane via its cage opening to reach bicyclooctatriene and then thermal rearrangement of bicyclooctatriene to produce [8]annulene which is the experimentally observed major product. The observed kinetic data at the MN15-L/maug-cc-pVTZ level of theory were in good agreement with the experimental results as compared to the CBS-QB3 method. The cage opening and the thermal rearrangement steps at the experimentally employed temperature of 520 K were exergonic and exothermic. The atmospheric rate constants calculated by means of the RRKM theory show that the cage opening is the rate-determining step. T…