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.

The oxidation of sulfides by chromium(V)

2003 ◽  
Vol 81 (1) ◽  
pp. 75-80 ◽  
Author(s):  
Carmela R Jackson Lepage ◽  
Lynn Mihichuk ◽  
Donald G Lee
Keyword(s):  
Electron Transfer ◽  
Molecular Orbital ◽  
Radical Cation ◽  
Oxygen Transfer ◽  
Single Electron ◽  
Frontier Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Single Electron Transfer ◽  
Oxidation Of Sulfides

The mechanism for the oxidation of sulfides by [(me4-salen)CrV(O)(pyO)]CF3SO3, where me4-salen is 8,8,8',8'-tetramethylsalen and pyO is pyridine N-oxide, has been investigated. Results from Hammett correlations on the rates of oxidation of substituted thioanisoles, frontier molecular orbital calculations, and product studies are consistent with a mechanism that is initiated by a single electron transfer to give a radical cation intermediate.Key words: oxidation, chromium(V), sulfides, radical cation, oxygen transfer.

Light harvesting subphthalocyanine–ferrocene dyads: Fast electron transfer process studied by femtosecond laser photolysis

2016 ◽  
Vol 20 (08n11) ◽  
pp. 1148-1155 ◽  
Author(s):  
Mohamed E. El-Khouly ◽  
Maged A. El-Kemary ◽  
Ahmed El-Refaey ◽  
Kwang-Yol Kay ◽  
Shunichi Fukuzumi
Keyword(s):  
Electron Transfer ◽  
Molecular Orbital ◽  
Charge Separation ◽  
Spectroscopic Studies ◽  
Frontier Molecular Orbital ◽  
Axial Position ◽  
Redox Potentials ◽  
Electron Transfer Process ◽  
Fast Charge ◽  
Lowest Unoccupied Molecular Orbital

Ferrocene-subphthalocyanine dyads characterized, where ferrocene is axially linked with subphthalocyanine at its axial position with the B–O bond through the para and metapositions, namely Fc–[Formula: see text]PhO–SubPc (dyad 1) and Fc–[Formula: see text]PhO–SubPc (dyad 2). The geometric and electronic structures of 1 and 2 were probed by ab initio B3LYP/6-311G methods. The optimized structures showed that the Fc and SubPc entities are separated by 8.42 and 7.40 Å for dyads 1 and2, respectively. The distribution of the highest occupied frontier molecular orbital (HOMO) was found to be located on the Fc entity, while the lowest unoccupied molecular orbital (LUMO) was located on the SubPc entity, suggesting that the charge-separated states of the are Fc[Formula: see text]–SubPc[Formula: see text]. Upon photoexcitation at the subphthalocyanine unit, both dyads undergo photoinduced electron transfer to form the corresponding charge-separated species, Fc[Formula: see text]–SubPc[Formula: see text]. Based on their redox potentials determined by cyclic voltammetry technique, the direction of the charge separation and the energies of these states have been revealed. Femtosecond transient spectroscopic studies have revealed that a fast charge separation of 8.8 × 10[Formula: see text] and 1.2 × 10[Formula: see text] s[Formula: see text] for 1 and 2, respectively, indicating fast charge separation in these simple dyads.

scholarly journals Frontier molecular orbital effects control the hole-catalyzed racemization of atropisomeric biaryls

2019 ◽  
Vol 10 (8) ◽  
pp. 2285-2289 ◽  
Author(s):  
Jacqueline S. J. Tan ◽  
Robert S. Paton
Keyword(s):  
Transition State ◽  
Molecular Orbital ◽  
Frontier Molecular Orbital ◽  
Highest Occupied Molecular Orbital ◽  
Planar Transition

Biaryl atropisomerization is dramatically accelerated by the removal of an electron. The planar transition state is preferentially stabilized from depopulation of the highest occupied molecular orbital.

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