Reaction of the OH Radical with Furfural. Spectral and Kinetic Investigation by Pulse Radiolysis and by ab Initio and Semiempirical Methods

1999 ◽  
Vol 103 (7) ◽  
pp. 858-864 ◽  
Author(s):  
Mila D'Angelantonio ◽  
Salvatore S. Emmi ◽  
Gabriella Poggi ◽  
Giancarlo Beggiato
Keyword(s):  
Ab Initio ◽  
Pulse Radiolysis ◽  
Semiempirical Methods ◽  
Oh Radical ◽  
Kinetic Investigation

Phenylalanine: Its ˙OH and SO4˙⁻-Induced Oxidation and Decarboxylation. A Pulse Radiolysis and Product Analysis Study

1993 ◽  
Vol 48 (6) ◽  
pp. 761-770 ◽  
Author(s):  
Degui Wang ◽  
Heinz-Peter Schuchmann ◽  
Clemens von Sonntag
Keyword(s):  
Radical Cation ◽  
Pulse Radiolysis ◽  
Side Reactions ◽  
Intramolecular Electron Transfer ◽  
Oh Radical ◽  
Product Analysis ◽  
Water Elimination ◽  
Deprotonation Reaction ◽  
Type Radical ◽  
Radical Yield

Phenylamine has been oxidized by radiolytically generated hydroxyl and sulfate radicals, the ensuing intermediates and their reactions have been studied by pulse radiolysis and product analysis in the absence and presence of oxidants such as Fe(CN)63- and O2. Upon OH radical attack, hydroxycyclohexadienyl-type radicals are mainly formed while Η-abstraction reactions can be neglected. In the presence of Fe(CN)63- these radicals are for the most part oxidized to the corresponding tyrosines (80%), except for the ipso-OH-adduct radicals (≈ 20%). It is concluded that ˙OH-addition is almost random, but with a slight avoidance of the metaposition relative to the ortho-, para- and ipso-positions. Oxygen adds reversibly to the OH-adduct radicals (kf = 1.8 × 108 dm3 mol-1 s-1, kr = 5.4 × 104 s-1). In this case, tyrosine formation occurs by HO2˙-elimination. However, due to side reactions, tyrosine formation only reaches 52% of the OH radical yield. The tyrosine yield drops to 10% in the absence of an oxidant.Upon SO4˙⁻-attack, decarboxylation becomes a major process (33% of SO4˙⁻) alongside the production of tyrosines (43%). Here, with Fe(CN)63- as the oxidant the formation of p-Tyr (18.5%) and m-Tyr (16.5%) is preferred over o-Tyr formation (8.5%). It is believed that in analogy to other systems a radical cation is formed immediately upon SO4˙⁻-attack which either reacts with water under the formation of hydroxycyclohexadienyl-type (“OH-adduct”) radicals, or decarboxylates after intramolecular electron transfer. The radical cation can also arise indirectly through H+-catalysed water elimination from the ˙OH-adduct radicals. At pH 2 and a dose rate of 0.0046 Gy s-1 CO2 formation matches the OH radical yield when ˙OH is the attacking radical. Below pH 2, G(CO2) decreases with falling pH. This indicates the occurrence of another, unimolecular, pathway under these conditions competing effectively with decarboxylation. This appears to be a relatively slow deprotonation reaction of the carboxylprotonated phenylalanine radical cation which gives rise to the benzyl-type radical.

[3,3] Sigmatropic Rearrangement of Some Fluorinated 1,5-Hexadienes

2002 ◽  
Vol 67 (10) ◽  
pp. 1517-1532 ◽  
Author(s):  
William R. Dolbier ◽  
Keith W. Palmer ◽  
Feng Tian ◽  
Piotr Fiedorow ◽  
Andrzej Zaganiaczyk ◽  
...  
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Transition States ◽  
Activation Parameters ◽  
Sigmatropic Rearrangement ◽  
Semiempirical Methods ◽  
Cope Rearrangement ◽  
Computational Studies ◽  
Stepwise Mechanism ◽  
Radical Intermediates

Fluorine atoms incorporated into 1,5-hexadiene molecule should influence the kinetic as well as the thermodynamic parameters of [3,3] sigmatropic rearrangement (Cope rearrangement). Within few decades is has been documented that this transformation proceeds in a concerted manner, rather than stepwise with some radical intermediates involved. Few new terminally fluorinated 1,5-hexadienes (compounds 3, 5A, 7, 9 and 5B) have been synthesized. The activation parameters of rearrangement have been determined and compared with those known for hydrocarbon analogues. While systems developing chair-like transition states (compounds 3 and 5) showed close similarity with hydrocarbon analogues (compound 1), those developing boat-like transition states (compounds 7, 9 and 5B) may proceed through radical stepwise mechanism. Computational studies of the transition states were carried out, showing that only ab initio methods (MP2 and especially DFT) can give approximate correlation with experimental data, whereas in the case of hydrocarbon analogues even simple semiempirical methods (AM1) were reliable enough to reproduce experimental results.

Ab Initio-Rechnungen zur Protonenaffinität unverzweigter primärer aliphatischer Amine / Ab Initio-Calculations on the Protonaffinity of Unbranched Primary Aliphatic Amines

1984 ◽  
Vol 39 (6) ◽  
pp. 593-595
Author(s):  
Eberhard Heyne ◽  
Gerhard Raabe ◽  
Jörg Fleischhauer
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Proton Affinity ◽  
Positive Charge ◽  
Semiempirical Calculations ◽  
Aliphatic Amines ◽  
Semiempirical Methods ◽  
Satisfactory Correlation ◽  
Primary Aliphatic Amines

Recently we reported the results of semiempirical calculations (MNDO, MINDO/3) which led us to the conclusion, that the proton-affinity of molecules R-NH2 (R = H, CH3, C2H5, n-C3H7 and n-C4H9) is determined by the ability of the groups R to carry positive charge in the corresponding cations R-NH3+. We did extend our investigations concerning the protonaffinities of primary aliphatic amines including NH3 and performed ab initio calculations with an STO-3G basis. The results qualitatively parallel those obtained by the semiempirical methods mentioned above. In contrast to the semiempirical results we found that there is a satisfactory correlation between the Mulliken-charges of the nitrogen-atoms and of the NH2-groups and the experimental protonaffinities if NH3 is excluded.

scholarly journals Laboratory Millimeter Wave Spectroscopy of Small Reactive Species

1994 ◽  
Vol 146 ◽  
pp. 417-431
Author(s):  
C. Demuynck ◽  
M. Bogey ◽  
H. Bolvin ◽  
M. Cordonnier ◽  
J.L. Destombes ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Millimeter Wave ◽  
Radio Astronomy ◽  
Molecular Ions ◽  
Reactive Species ◽  
Oh Radical ◽  
Line Frequency ◽  
Millimeter Wave Spectroscopy ◽  
Strong Motivation

The discovery of a large variety of molecules by radio astronomy has been a very strong motivation for the development of laboratory millimeter wave spectroscopy. Among them, the reactive species, neutral and/or ionic, have been early recognized as playing a very important role in the chemistry of the interstellar and circumstellar medium. While the laboratory spectroscopy of free radicals started relatively early, with the observation of the OH radical by the group of Townes (Dousmanis et al. 1955), the detection of molecular ions proved to be a much more difficult task, and the first millimeter line due to an ion was actually detected by radio astronomy (Buhl & Snyder 1970). It was called “U89.2” until it was tentatively attributed to HCO+by Klemperer (1970) on the basis of both considerations on the chemistry of the interstellar medium, and of ab initio calculations for the prediction of the expected line frequency. This identification was later confirmed by more elaborated ab initio calculations (Wahlgren et al. 1973, Kraemers & Diercksen 1976), and by the observation of a transition attributed to H13CO+(Snyder et al. 1976), but the definite confirmation was the observation of the same transition in a laboratory glow discharge by the group of Woods (Woods et al. 1975).

Ab initio Calculation of the Dipole Moment Function of the OH Radical Ground State

2018 ◽  
Vol 12 (6) ◽  
pp. 970-976
Author(s):  
S. O. Adamson ◽  
D. D. Kharlampidi ◽  
G. V. Golubkov ◽  
M. I. Manzhelii ◽  
S. S. Nabiev ◽  
...  
Keyword(s):  
Dipole Moment ◽  
Ab Initio ◽  
Ground State ◽  
Ab Initio Calculation ◽  
Moment Function ◽  
Oh Radical

Reactions of OH Radicals with Acetylacetone in Aqueous Solution. A Pulse Radiolysis and Electron Spin Resonance Study

1982 ◽  
Vol 37 (3) ◽  
pp. 368-375 ◽  
Author(s):  
R. K. Broszkiewicz ◽  
T. Söylemez ◽  
D. Schulte-Frohlinde
Keyword(s):  
Double Bond ◽  
Pulse Radiolysis ◽  
Visible Region ◽  
Alkaline Condition ◽  
Main Reaction ◽  
Electron Spin Resonance Study ◽  
Oh Radicals ◽  
Oh Radical ◽  
Keto Form ◽  
Optical Absorbance

Abstract Pulse radiolysis experiments monitoring optical absorbance as well as conductivity and in-situ ESR radiolysis studies show that the OH radical reacts with the enol (k=8.6 x 109 M-1 s-1) and the enolate (k = 7.4 X 109 M-1 s-1) forms of acetylacetone by addition to the C = C double bond in aqueous N2O saturated solution. The OH reaction with enol leads to equal amounts of two radicals, CH3COCHOHCOHCH3 (2) and CH3COCHC(OH)2CH3 (4), as determined by scavenger reactions. At pH less than 1 the radical CH3COCHCOCH3 (1) is observed by ESR spectroscopy showing that radical 2 and/or 4 eliminate water by proton catalyzed reactions. Under alkaline condition the OH adducts to the enolate eliminate OH -with rate constants larger than 105 s-1 leading to radical 1. G(OH-) is determined to be 5.6 showing that addition is the main reaction of OH with enolate. To a much smaller degree the OH radical is proposed to abstract an H atom from that CH3 group which is attached to the C -C double bond in enol and enolate, producing substituted allyl radicals which absorb in the visible region. The reaction of OH with the keto form has not been observed indicating that the rate constant of this reaction is significantly smaller than those with enol and enolate.

Oxidation of Silver Cyanide Ag(CN)2– by the OH Radical: From Ab Initio Calculation to Molecular Simulation and to Experiment

2020 ◽  
Vol 124 (51) ◽  
pp. 10787-10798
Author(s):  
Céline Léonard ◽  
Frédéric Le Quéré ◽  
Daniel Adjei ◽  
Sergey A. Denisov ◽  
Mehran Mostafavi ◽  
...  
Keyword(s):  
Ab Initio ◽  
Molecular Simulation ◽  
Ab Initio Calculation ◽  
Oh Radical ◽  
Silver Cyanide
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