scholarly journals Radical Chain Monoalkylation of Pyridines

2021 ◽  
Author(s):  
Samuel Rieder ◽  
Camilo Meléndez ◽  
Kleni Mulliri ◽  
Philippe Renaud
Keyword(s):  
Rate Constant ◽  
Iodine Atom ◽  
Radical Chain ◽  
Enol Ethers ◽  
Alkyl Radicals ◽  
Reaction Proceeds ◽  
Order Of Magnitude ◽  
Enol Esters ◽  
The One ◽  
Neutral Conditions

<p>The monoalkylation of N-methoxypyridinium salts with alkyl radicals generated from alkenes (via hydroboration with catecholborane), alkyl iodides (via iodine atom transfer) and xanthates is reported. The reaction proceeds under neutral conditions since no acid is needed to activate the heterocycle and does not require the use of an external oxidant. A rate constant for the addition of a primary radical to N-methoxylepidinium >107 M–1 s–1 was experimentally determined. This rate constant is more than one order of magnitude larger than the one measured for the addition of primary alkyl radical to protonated lepidine demonstrating the remarkable reactivity of methoxypyridinium salts towards radicals. The reaction could be extended to a three component carbopyridinylation of electron rich alkenes including enol esters, enol ethers and enamides.</p>

scholarly journals Organoboron Mediated Homolytic Aromatic Substitution of N-Methoxypyridinium Salts

2021 ◽  
Author(s):  
Samuel Rieder ◽  
Camilo Meléndez ◽  
Kleni Mulliri ◽  
Philippe Renaud
Keyword(s):  
Rate Constant ◽  
Aromatic Substitution ◽  
Enol Ethers ◽  
Alkyl Radicals ◽  
Homolytic Aromatic Substitution ◽  
Reaction Proceeds ◽  
Order Of Magnitude ◽  
Enol Esters ◽  
The One ◽  
Neutral Conditions

<p>The monoalkylation of N-methoxypyridinium salts with alkyl radicals generated from alkenes (via hydroboration with catecholborane), alkyl iodides (via iodine atom transfer) and xanthates is reported. The reaction proceeds under neutral conditions since no acid is needed to activate the heterocycle and does not require the use of an external oxidant. A rate constant for the addition of a primary radical to N-methoxylepidinium >107 M–1 s–1 was experimentally determined. This rate constant is more than one order of magnitude larger than the one measured for the addition of primary alkyl radical to protonated lepidine demonstrating the remarkable reactivity of methoxypyridinium salts towards radicals. The reaction could be extended to a three component carbopyridinylation of electron rich alkenes including enol esters, enol ethers and enamides.</p>

scholarly journals Organoboron Mediated Homolytic Aromatic Substitution of N-Methoxypyridinium Salts

2021 ◽  
Author(s):  
Samuel Rieder ◽  
Camilo Meléndez ◽  
Kleni Mulliri ◽  
Philippe Renaud
Keyword(s):  
Rate Constant ◽  
Aromatic Substitution ◽  
Enol Ethers ◽  
Alkyl Radicals ◽  
Homolytic Aromatic Substitution ◽  
Reaction Proceeds ◽  
Order Of Magnitude ◽  
Enol Esters ◽  
The One ◽  
Neutral Conditions

<p>The monoalkylation of N-methoxypyridinium salts with alkyl radicals generated from alkenes (via hydroboration with catecholborane), alkyl iodides (via iodine atom transfer) and xanthates is reported. The reaction proceeds under neutral conditions since no acid is needed to activate the heterocycle and does not require the use of an external oxidant. A rate constant for the addition of a primary radical to N-methoxylepidinium >107 M–1 s–1 was experimentally determined. This rate constant is more than one order of magnitude larger than the one measured for the addition of primary alkyl radical to protonated lepidine demonstrating the remarkable reactivity of methoxypyridinium salts towards radicals. The reaction could be extended to a three component carbopyridinylation of electron rich alkenes including enol esters, enol ethers and enamides.</p>

scholarly journals Radical Chain Monoalkylation of Pyridines

2021 ◽  
Author(s):  
Samuel Rieder ◽  
Camilo Meléndez ◽  
Fabrice Dénès ◽  
Kleni Mulliri ◽  
Harish Jangra ◽  
...  
Keyword(s):  
Iodine Atom ◽  
Atom Transfer ◽  
Radical Chain ◽  
Alkyl Radicals ◽  
Reaction Proceeds ◽  
Alkyl Iodides

The monoalkylation of N-methoxypyridinium salts with alkyl radicals generated from alkenes (via hydroboration with catecholborane), alkyl iodides (via iodine atom transfer) and xanthates is reported. The reaction proceeds under neutral...

The oxidation of neopentane

1969 ◽  
Vol 308 (1494) ◽  
pp. 305-325 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Gas Phase ◽  
Static System ◽  
Radical Chain ◽  
Phase Oxidation ◽  
Reaction Proceeds ◽  
Gas Phase Oxidation ◽  
Branched Chain ◽  
The One ◽  
Heterogeneous Chain

The gas phase oxidation of neopentane has been studied in a static system at 280 °C. It is shown that the main course of the reaction is best understood as a degenerately branched chain reaction propagated by the hydroxyl radical. Two simultaneous radical chain mechanisms arise from the decomposition of the transient unstable species neopentylperoxy to give on the one hand either isobutyraldehyde and carbon monoxide, or isobutene and acetone, and on the other hand isobutene and formaldehyde possibly via oxetane. Isobutene and isobutyraldehyde do not accumulate as end products of the reaction, but are further oxidized to acetone and carbon monoxide. Pivalaldehyde and isobutene are the first detectable intermediate products, and the former is primarily responsible for the degenerate branching mechanism. It is concluded that the accumulation of formaldehyde in the system can account for an apparent change from homogeneous to heterogeneous chain termination as the reaction proceeds.

Trajectory study of dissociation reactions. Br2 in Ar at 3500 K

1977 ◽  
Vol 55 (3) ◽  
pp. 380-382 ◽  
Author(s):  
D. T. Chang ◽  
George Burns
Keyword(s):  
High Temperatures ◽  
Rate Constant ◽  
Rate Coefficient ◽  
Dissociation Rate ◽  
Experimental Results ◽  
Dissociation Rate Constant ◽  
Trajectory Calculations ◽  
Order Of Magnitude ◽  
Nonequilibrium Effects ◽  
The One

Dissociation of Br2 in Ar was studied at 3500 K using classical 3-D trajectory technique, and compared with earlier trajectory calculations. Some of the assumptions used previously were eliminated, while others were studied in some detail. The one-way flux, equilibrium rate coefficient, obtained from over 8400 trajectories, was found to be over an order of magnitude larger than the experimental rate constant. This was taken as an indication that at high temperatures the nonequilibrium effects are important in dissociation reactions. In order to understand these effects better, additional calculations using an improved set of assumptions were performed. The calculated dissociation rate constant for Br2 + Ar → 2Br + Ar reaction, which accounted for nonequilibrium effects, agrees reasonably well with experimental results.

Rate constant for chlorine abstraction from CCl4 by the 5-hexenyl radical

1987 ◽  
Vol 65 (2) ◽  
pp. 311-315 ◽  
Author(s):  
Deborah Rae Jewell ◽  
Lukose Mathew ◽  
John Warkentin
Keyword(s):  
Free Radical ◽  
Double Bond ◽  
Chlorine Atom ◽  
Rate Constant ◽  
Methyl Ethyl ◽  
Chain Mechanism ◽  
Secondary Product ◽  
Radical Chain ◽  
Alkyl Radicals ◽  
Primary Products

Cyclization of the 5-hexenyl free radical to the cyclopentylmethyl free radical was used to clock chlorine atom abstraction by 5-hexenyl from carbon tetrachloride in solution. The source of 5-hexenyl radicals was 5-hexenyl[1-hydroxy-1-methyl-ethyl]diazene ((CH3)2C(OH)N=N(CH2)4CH=CH2), which decomposes thermally in CCl4 by a radical chain mechanism to afford chloroform, acetone, nitrogen, 6-chloro-1-hexene, cyclopentylchloromethane, 1-hexene, and methylcyclopentane as primary products. 6-Chloro-1-hexene is converted, in part, to a secondary product, 1,1,1,3,7-pentachloroheptane, by radical chain addition of CC14 to the double bond. The rate constant for chlorine atom abstraction, kCl, was calculated from the product composition and the known rate constant for cyclization of the 5-hexenyl radical. For the temperature range 274–353 K, kCl is given by log (kCl/M−1 s−1) = (8.4 ± 0.3) − (6.2 ± 0.4)/θ where θ = 2.3 RT kcal mol−1, which leads to [Formula: see text]. This value is significantly smaller than recently reported estimates for other primary alkyl radicals.

Theoretical studies on the one- and two-photon absorption of tetrabenzoporphyrins and phthalocyanines

2004 ◽  
Vol 82 (1) ◽  
pp. 19-26 ◽  
Author(s):  
Xin Zhou ◽  
Ai-Min Ren ◽  
Ji-Kang Feng ◽  
Xiao-Juan Liu
Keyword(s):  
Dipole Moment ◽  
Cross Sections ◽  
Density Functional ◽  
Transition Dipole Moment ◽  
Photon Absorption ◽  
Transition Dipole ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Order Of Magnitude ◽  
The One

The one-photon absorption (OPA) properties of tetrabenzoporphyrins (TBPs) and phthalocyanines (Pcs) were studied using the semiempirical ZINDO method and time-dependent density functional theory (TDDFT), respectively. The compared results confirmed that the semiempirical ZINDO method was reasonably reliable when calculating the OPA of tetrabenzoporphyrins and phthalocyanines. On the basis of the OPA properties obtained from the ZINDO method, two-photon absorption (TPA) properties of two series of molecules were investigated, using ZINDO and sum-over-states (SOS) methods. The results showed that the TPA cross-sections of all molecules were in the range of 220.6 × 10–50 – 345.9 × 10–50 cm4·s·photon–1, which were in the same order of magnitude as the values reported in the literature. The relatively larger δ(ω) value for Pcs with respect to that for corresponding TBPs originates from larger intramolecular charge transfer, which can be characterized by the difference of dipole moment between S0 and S1 and the transition dipole moment between S1 and S5.Key words: two-photon absorption, ZINDO, sum-over-states, tetrabenzoporphyrin, phthalocyanines.

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