Competition between reactive sites during the pulse radiolysis of styrene in aqueous solution

1984 ◽  
Vol 37 (10) ◽  
pp. 2137 ◽  
Author(s):  
NA McAskill ◽  
DF Sangster
Keyword(s):  
Aqueous Solution ◽  
Aromatic Ring ◽  
Pulse Radiolysis ◽  
Reaction Pathways ◽  
Side Chain ◽  
Transient Species ◽  
Radiolysis Products

The optical absorptions of the transient species formed by the reactions of the primary radiolysis products of water (eaq-, ·H, and ·OH) with styrene were measured. There are large differences between the various literature estimates for these reaction pathways. Most of the eaq- and H and about 50% of the OH react with the unsaturated vinyl side chain to give the α-methylbenzyl and hydroxy-substituted methylbenzyl radical respectively. The remaining OH reacts with the aromatic ring to give hydroxy(vinyl)cyclohexadienyl radicals.

Influence of Solvent Composition (Water—Dioxane Mixtures) on the Formation Degree of Intramolecular Aromatic-Ring Stacks in Binary Cu(L-Phenylalaninate)2, Cu(L-Tryptophanate)2, and Related Complexes

1989 ◽  
Vol 44 (12) ◽  
pp. 1555-1566 ◽  
Author(s):  
Guogang Liang ◽  
Helmut Sigel
Keyword(s):  
Aqueous Solution ◽  
Organic Solvent ◽  
Aromatic Ring ◽  
Side Chain ◽  
Amino Acid Side Chain ◽  
High Concentrations ◽  
General Experience ◽  
Solvent Molecules ◽  
The Stability ◽  
Hydrophobic Solvation

The stability constants of the binary Cu(AA)+ and Cu(AA)2 complexes, where AA⁻ = L-phenyl-alaninate (Phe⁻) or L-tryptophanate (Trp⁻), have been determined by potentiometric pH titrations in water, and in 30, 50, 70 and 80% (v/v) dioxane—water mixtures (I = 0.1 M, NaNO3; 25 °C); the corresponding data for the complexes with L-alaninate (Ala⁻), L-valinate (Val⁻), L-norvalinate (Nva⁻), and L-leucinate (Leu⁻) are taken from our recent work (G. Liang, R. Tribolet, and H. Sigel, inorg. Chim. Acta 155, 273 (1989)). The overall stability of Cu(AA)+ and Cu(AA), is governed for all amino acetates (AA⁻) by the polarity of the solvent, while the extent of the intramolecular stack formation between the aromatic side chains in Cu(AA)2 is influenced by the hydrophobic solvation properties of the organic solvent molecules (i.e., the ethylene units of dioxane). Based on the stability difference Δ log K*AA = log KCu(AA)Cu(AA)2-log KCu(AA)Cuit is shown that Cu(Phe)2 and Cu(Trp)2 are more stable than Cu(Ala)2, and this increased stability is used for evaluating the extent of the stack formation (= closed form) in Cu(Phe)2 and Cu(Trp)2: the percentages of the closed forms vary between about 25 and 80% (based on Cu(AA),2/tot,), and those for Cu(Val)2, Cu(Leu)2 and Cu(Nva)2 between about 10 and 30%. The formation degree of the intramolecular side-chain adduct in Cu(AA)2 decreases (in most solvents), as one might expect, within the series: Cu(Trp)2 > Cu(Phe)2 > Cu(Val)2≳ Cu(Leu)2≳ Cu(Nva)2. The corresponding observations are made with M(AA)2 complexes of Co2+, Ni2+, and Zn2+. The influence of the organic solvent on the intramolecular hydrophobic and stacking adducts differs somewhat: (i) Stack formation in Cu(Phe)2 and Cu(Trp)2 is slightly inhibited by the presence of dioxane, but even in 50% (v/v) dioxane—water the formation degree of the aromatic-ring stacks is still more than 50%. (ii) Addition of some dioxane to an aqueous solution containing Cu(Val)2, Cu(Leu)2or Cu(Nva)2 favors the formation of the aliphatic side-chain adducts; the largest formation degree being reached close to a content of 70% dioxane. Both observations contrast with the general experience made at unbridged hydrophobic or stacking adducts: these are considerably destabilized already by the addition of relatively small amounts of an organic solvent to an aqueous solution. Such a destabilization of the closed Cu(AA)2 species occurs only at high concentrations of the organic solvent (usually more than 70%). It should be added that the organic solvent most probably influences the structure of the intramolecular ligand-ligand adducts giving rise to a whole series of “closed” species; a resolution is presently not possible and therefore the whole stability increase is attributed to a (single) so-called “closed” species to allow a quantification of the effect. The relevance of amino acid side-chain interactions regarding cooperativity, selectivity, evolutionary aspects, and low polarity regions, as in active-site cavities of proteins, are shortly indicated.

Pulse Radiolysis Study of Aqueous Solution Reactivity of Transient Species of Biological Interest: Reactions with Various Substrates

1988 ◽  
pp. 121-128
Author(s):  
A. Sekaki ◽  
K. Benzineb ◽  
G. Machtalere ◽  
C. Houée-Levin ◽  
M. Gardès-Albert ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Pulse Radiolysis ◽  
Transient Species ◽  
Biological Interest

Pulse radiolysis of polymers in aqueous solution. Kinetics study

1997 ◽  
Vol 94 ◽  
pp. 244-250 ◽  
Author(s):  
I Janik ◽  
P Kujawa ◽  
P Ulanski ◽  
JM Rosiak
Keyword(s):  
Aqueous Solution ◽  
Pulse Radiolysis ◽  
Kinetics Study ◽  
Solution Kinetics

Über den Mechanismus der Bildung von Polyanionen in wäßriger Lösung. Zum Bildungsmechanismus eines Polytetramolybdations [Mo4O144-]n / On the Mechanism of Formation of Polyanions in Aqueous Solution. Concerning the Mechanism of Formation of a Polytetramolybdate Ion [Mo4O144-]n

1976 ◽  
Vol 31 (6) ◽  
pp. 737-748 ◽  
Author(s):  
Karl-Heinz Tytko
Keyword(s):  
Aqueous Solution ◽  
Coordination Sphere ◽  
Analytical Formula ◽  
Reaction Pathways ◽  
Mechanism Of Formation ◽  
X Ray ◽  
Theoretical Considerations

Possible structures and the pertinent reaction pathways for the polymetalate ion present in a slightly soluble polymetalate having the analytical formula A2O · 2 MOs have been derived on the basis of theoretical considerations. Structure and kind of combination of the tetrameric units of one of the possibilities are in agreement with the results of X-ray structure analyses. First the previously proposed planar tetrametalate ion [M4O12(OH)4]4--is formed by stepwise aggregation according to an addition mechanism. This species undergoes a rearrangement of the coordination sphere of two of the M atoms and is then subject to a polycondensation resulting in a polytetrametalate chain, [M4O144-]n.

scholarly journals Dihydroquinolines, Dihydronaphthyridines and Quinolones by Domino Reactions of Morita-Baylis-Hillman Acetates

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 890
Author(s):  
Joel K. Annor-Gyamfi ◽  
Ebenezer Ametsetor ◽  
Kevin Meraz ◽  
Richard A. Bunce
Keyword(s):  
Aromatic Ring ◽  
Aromatic Amines ◽  
Control Experiment ◽  
Ring Closure ◽  
Domino Reaction ◽  
Side Chain ◽  
Initial Reaction ◽  
Dual Reactivity ◽  
Michael Acceptor ◽  
Nitrogen Nucleophile

An efficient synthetic route to highly substituted dihydroquinolines and dihydronaphthyridines has been developed using a domino reaction of Morita-Baylis-Hillman (MBH) acetates with primary aliphatic and aromatic amines in DMF at 50–90 °C. The MBH substrates incorporate a side chain acetate positioned adjacent to an acrylate or acrylonitrile aza-Michael acceptor as well as an aromatic ring activated toward SNAr ring closure. A control experiment established that the initial reaction was an SN2′-type displacement of the side chain acetate by the amine to generate the alkene product with the added nitrogen nucleophile positioned trans to the SNAr aromatic ring acceptor. Thus, equilibration of the initial alkene geometry is required prior to cyclization. A further double bond migration was observed for several reactions targeting dihydronaphthyridines from substrates with a side chain acrylonitrile moiety. MBH acetates incorporating a 2,5-difluorophenyl moiety were found to have dual reactivity in these annulations. In the absence of O2, the expected dihydroquinolines were formed, while in the presence of O2, quinolones were produced. All of the products were isolated in good to excellent yields (72–93%). Numerous cases (42) are reported, and mechanisms are discussed.

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