Anionic reactions, molecular

F. J. Luque, M. Orozco, P. K. Bhadane and S. R. Gadre, Effect of solvation on the shapes, sizes, and anisotropies of polyatomic anions via molecular electrostatic potential topography An ab initio self-consistent reaction field approach, J. Chem. Phys., 100 (1994) 6718-6726. 

In most experiments and applications with titanium dioxide photocatalysts, molecular oxygen is present to act as the primary electron acceptor. Usually the electrons trapped as Ti(III) are transferred to dioxygen adsorbed at the semiconductor surface yielding peroxyl radical anions (reaction (7.16)) [16]. 

Molander has also studied the Sml2-mediated double Barbier additions of alkyl dihalides to ketoesters.22,23 These impressive anionic-anionic, inter-molecular-intramolecular sequences require the use of Nil2 as an additive and irradiation with visible light and allow access to a range of bicyclic and tricyclic systems. The reactions proceed by reduction of the more reactive alkyl halide, intermolecular Barbier addition to the ketone, lactonisation and a second Barbier addition to the lactone carbonyl (Scheme 6.18).22... 

This shift was interpreted with the aid of DFT calculations in terms of molecular conformational changes of (NpS.. SNp)" radical anion due to the elongation of the S-S bond from 0.213 nm in a rigid matrix at 77 K up to 0.290 nm in fluid phase at 273 K. The (NpS.. SNp)" radical anion dissociates into napthylthiyl radical and thionaphtholate anion [reaction (38)] in DMF solution at 293 K with a first-order rate constant k= 10 s"h... 

The free radical(s) so formed are then scavenged by molecular oxygen forming the peroxy radical or anion (Reaction 5) thus leading to the oxidation of the acceptor AH. This is called the Type I mechanism of photooxidation. 

In the presence of other molecular species, a chain reaction involving conversion of a primary radical to a secondary species has sometimes been observed for example, the p-methylphenoxyl radical from HRP/H2O2 oxidation of p-cresol has been shown [121] to oxidize ascorbate to the corresponding radical anion. Reactions of this kind can be extremely effective. 

Mokcular sieves have potentiai uses as catalysts for vinyl polymerization reactions. They have been widely used as cationic catalysts, and in a limited numbo of instances in anionic polymerisation reactions. Molecular sieves also find uses as polymer modifiers bringing m defbdte improvements in their properties. 

It should be emphasised that the solvent activity coefficients recorded to date are of greatest value in reactions involving at least one ionic species as a reactant or product, in particular bimolecular nucleophilic attack by anions and molecular solvolyses producing ionic products. These reactions show the greatest sensitivity to solvent change and thus the relatively imprecise values of these activity coefficients do not endanger the validity of the interpretation. Allowance for solute non-ideality in terms of Debye-Huckel activity coefficients and on association can be made in principle, but is time consuming and requires both additional care and more experiments than have been done, indeed warranted, to date. 

Recently, the Chi group disclosed an NHC-promoted asymmetric inter-molecular cross-aza-benzoin reaction of enals with isatin-derived ketimines to afford chiral quaternary 3-aminooxindoles (18 examples, with up to 76% yield, 96% ee). The chemoselectivity is controlled by the NHC catalysts, with electron-deficient and sterically non-congested carbene catalysts favoring the enal acyl anion reaction pathway and aza-benzoin, allowing convenient access to products of different scaffolds by starting from the same set of readily available substrates (Scheme 7.16). 

At its essence, a conjugated system involves at least one atom with ap orbital adjacent to at least one tt bond. The adjacent atom with the p orbital can be part of another ir bond, as in 1,3-butadiene, or a radical, cationic, or anionic reaction intermediate. If an example derives specifically from a propenyl group, the common name for this group is allyl. In general when we are considering a radical, cation, or anion that is adjacent to one or more TT bonds in a molecule other than propene, the adjacent position is called allylic. Below we show the formula for butadiene, resonance hybrids for the allyl radical and an allylic carbocation, and molecular orbital representations for each one. 

The mechanism is believed to begin by SET from the base to the aryl iodide to form a radical anion. Inter-molecular reaction can occnr through a HAS, the radical variant of the more commonly known EAS reaction. For intermolecular reaction, addition of the radical to the coupling partner resnlts in a resonance-stabilized radical. Deprotonation with base forms a biaryl radical anion which propagates the mechanism by donating an electron to another aryl haUde. For intra-molecular reaction, the aryl radical likely adds to the ipso position of the tether. Subsequent ring expansion and re-aromatization yields the prodnct. ... 

The uncatalyzed thermal oxidation of atactic polystyrene has been studied extensively, including main chain deuterated derivatives. Such studies are usually conducted around 475 K over the course of hours. However, in preliminary infrared studies with cast films of anionic polystyrene (molecular weight 4,(X)0) on a AgQ plate, carbonyl bonds were first detected after 10 minutes heating in air at 403 Oxidation is an exothermic reaction. We have not located a measured heat of oxidation. However, comparisons with the heats of combustion for ethylbenzene and acetophenone in the Handbook of Chemistry and Physics indicate a liberation of 102 kcal/mol for the oxidation of ethylbenzene to acetophenone. The course of oxidation of polystyrene is a complex chain reaction but we will assume a net heat of liberation of = 100 kcal/mol to hold. 

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