scholarly journals Is Aromatic Nitration Spin Density Driven?

Chemistry ◽  
2021 ◽  
Vol 3 (4) ◽  
pp. 1286-1301
Author(s):  
Amedeo Capobianco ◽  
Alessandro Landi ◽  
Andrea Peluso
Keyword(s):  
Electron Transfer ◽  
Gas Phase ◽  
Radical Pair ◽  
Theoretical Data ◽  
Point Of View ◽  
Positional Selectivity ◽  
Solvent Polarization ◽  
Quantum Chemical Computations ◽  
Aromatic Nitration

The mechanism of aromatic nitration is critically reviewed with particular emphasis on the paradox of the high positional selectivity of substitution in spite of low substrate selectivity. Early quantum chemical computations in the gas phase have suggested that the retention of positional selectivity at encounter-limited rates could be ascribed to the formation of a radical pair via an electron transfer step occurring before the formation of the Wheland intermediate, but calculations which account for the effects of solvent polarization and the presence of counterion do not support that point of view. Here we report a brief survey of the available experimental and theoretical data, adding a few more computations for better clarifying the role of electron transfer for regioselectivity.

On the theory of electron-transfer processes in aqueous solutions

1954 ◽  
Vol 222 (1148) ◽  
pp. 128-141 ◽  
Keyword(s):  
Electron Transfer ◽  
Point Of View ◽  
Complex Ions ◽  
Gaseous State ◽  
Biochemical Processes ◽  
Transfer Processes ◽  
Oxidation Reduction ◽  
Mechanical Interpretation ◽  
Electron Transfer Processes

It has been realized for some time that simple electron-transfer processes play an important part in the mechanism of many oxidation-reduction reactions in solution. An attempt has been made to give a quantum-mechanical interpretation of these processes on the basis of the earlier theories of electron transfer in the gaseous state (Landau 1932; Bates & Massey 1943). The present treatment for solutions takes into account the role of the solvent, with particular reference to the operation of the Franck—Condon principle and it also leads to some definite picture of the transition state for the electron transfer process. A number of examples are discussed, including electron transfer between like ions of different valency and also reactions involving complex ions, e.g. metal porphyrins, the reactions of which are of importance in certain biochemical processes. It appears that the application of certain theoretical principles leads to a satisfactory understanding of electron-transfer processes in solution from a qualitative and, in some cases, also from a semi-quantitative point of view.

Role of electron transfer in gas-phase ligand-switching reactions

1991 ◽  
Vol 10 (4) ◽  
pp. 1089-1094 ◽  
Author(s):  
Steven L. VanOrden ◽  
R. Marshall. Pope ◽  
Steven W. Buckner
Keyword(s):  
Electron Transfer ◽  
Gas Phase

scholarly journals Gas-phase electrophilic aromatic substitution mechanism with strong electrophiles explained by ab initio non-adiabatic dynamics

2014 ◽  
Vol 16 (35) ◽  
pp. 18686-18689 ◽  
Author(s):  
Daniel Kinzel ◽  
Shmuel Zilberg ◽  
Leticia González
Keyword(s):  
Electron Transfer ◽  
Ab Initio ◽  
Gas Phase ◽  
Radical Pair ◽  
Electrophilic Aromatic Substitution ◽  
Single Electron Transfer ◽  
Aromatic Substitution ◽  
Substitution Reactions ◽  
Substitution Mechanism ◽  
Adiabatic Dynamics

Ultrafast single electron transfer producing a radical pair governs the formation of a σ-complex in gas-phase electrophilic aromatic substitution reactions.

INSIGHTS INTO THE SOLVATO-/THERMO-PROMOTED INTRAMOLECULAR ELECTRON TRANSFER IN A TTF-σ-TCNQ DYAD WITH AN EXTREMELY LOW HOMO–LUMO GAP

2012 ◽  
Vol 11 (03) ◽  
pp. 599-609 ◽  
Author(s):  
YUHUA ZHOU ◽  
KAI TAN ◽  
XIN LU
Keyword(s):  
Electron Transfer ◽  
Gas Phase ◽  
Ground State ◽  
Polar Solvent ◽  
Closed Shell ◽  
Open Shell ◽  
Polarizable Continuum Model ◽  
Intramolecular Electron Transfer ◽  
Singlet Ground State ◽  
Solvent Polarization

The low-lying states of an organic donor-σ-acceptor dyad, i.e. tetrathiafulvalene-σ-tetracyano-p-quinodimethane (TTF-σ-TCNQ), in gas phase and in various solvents have been investigated by means of hybrid DFT calculations in combination with the conductor-like polarizable continuum model to describe solvent effects. It has been shown that the dyad, though preferring a closed-shell singlet ground state with an eclipsed conformation in gas phase, adopts the charge-separated zwitterionic states with an extended conformation (TTF+-σ-TCNQ-), i.e. open-shell singlet biradical ground state immediately followed by triplet biradical state, in polar solvent ( CH3CN and CH2Cl2 ) as a result of the intramolecular electron transfer (ET) stimulated by solvent polarization. The degree of such intramolecular ET is so strongly dependent on the polarity (dielectric constant) of solvent that the zwitterionic biradical states become more stable with respect to the closed-shell singlet state with increasing polarity of the solvent. As such, the dyad should show a higher ratio of biradicals in more polar solvent and/or at higher temperature and, hence, is chameleonic in nature.

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