Electrophilic properties

Bromine although it adds rapidly to alkenes is too weak an electrophile to react at an appreciable rate with benzene A catalyst that increases the electrophilic properties of bromine must be present Somehow carpet tacks can do this How7... 

The boron atom in boron trifluoride is hybridized to the sp planar configuration and consequently is coordinatively unsaturated, ie, a Lewis acid. Its chemistry centers around satisfying this unsaturation by the formation with Lewis bases of adducts that are nearly tetrahedral sp [ The electrophilic properties (acid strengths) of the trihaloboranes have been found to increase in the order BF < BCl < BBr < BI (3,4). 

The enhancement of the electrophilic properties of thaHium(III) ttifluoroacetate makes it a very important thaHation reagent. The products of thaHation, eg, arylthaHium bis(ttifluoracetate), undergo a variety of substitution reactions, yielding iodides, fluorides, nitriles, thiophenols, phenols, and biaryls. 

One way to investigate the electrophilic properties of these molecules is to examine the orbital that each uses to accept electrons from a nucleophile. This orbital is the lowest-unoccupied molecular orbital (LUMO). Examine the LUMO for methyl acetate (Z=OCH3), acetaldehyde (Z=H), N,N-dimethylacetamide (Z=N(CH3)2) and acetyl chloride (Z=C1) (acetaldehyde is not a carboxylic acid derivative, but is included here for comparison). What is the shape of the LUMO in the region of the carbonyl group Is it a o or 7U orbital Is it bonding or antibonding What other atoms contribute to the LUMO Which bonds, if any, would be weakened when a nucleophile transfers its electrons into the LUMO ... 

The aminobutynones 342 contain a push-pull system with a strongly electron-withdrawing carbonyl group therefore, they show electrophilic properties. Cyclizations with their participation proceed differently from those with ynamines (91UK103 00UK642) and acetylenic ketones (73UK511). 

Cyanine Dyes Derived from Thiazolium Salts 1. Electrophilic Properties of Thiazolium Salts... 

The carbonyl group also possesses electrophilic properties at the carbon atom and nucleophilic properties at the oxygen atom. Nucleophilic attack of the carbonyl group is favored if this is attached to an aromatic ring (inductive effect) and there is also a methoxy or phenolic OH group present in the 4-position. Changing a neutral reaction medium by proton addition has the same effect. 

In the latter case the M—N—O moiety is highly bent (130-140°), the N—O bond length shortened and its polarization increased by about three times in comparison to free NO molecule. Such changes indicate that the NO acquires electrophilic properties upon the coordination, and is characterized by vNO > 1850 cm-1 [53], Examples are given by the p fCoNO 8, 171 NiNO 9, and 171 CuNO 10 complexes. 

Synthetic use can be made of the potent electrophilic properties of ADC compounds by transforming the initial adducts into heterocyclic products. For example, reaction of DEAZD with enamine 92 gives the substitution product 93 in quantitative yield. Further treatment of this initial adduct with acid, followed by base hydrolysis leads to benzoxazol-2-ones. The dimethyl substituted enamine (92, R = Me) gives the rare, but isolable 6//-benzoxazol-2-one ring system (Scheme 13).147... 

Although diselenonium-, ditelluronium- and mixed sulfonium-selenonium dications can exhibit either oxidative or electrophilic properties in reactions with nucleophiles, substitution at the onium chalcogen atom is more typical.96 Owing to the increased stability of heavier dichalcogenium-dications, they react only with highly activated substrates such as aniline and tV,A-dimethylaniline, while no reaction is observed with phenol and diphenylamine.113 Reactions of ditelluronium dications with activated aromatics are also not known (Scheme 44).114... 

These findings, and extensive subsequent work, are consistent with a singlet ground state for this species. The chemical reactivity of these carbenes towards olefins can be related empirically but quantitatively to the electronic properties of the substituents (Moss et al., 1977 Moss, 1980). An extreme example is dimethoxycarbene which does not exhibit at all the electrophilic properties normally associated with the vacant non-bonding orbital of a singlet carbene (Lemal et al., 1966). These findings are easily understood by... 

Structure B is of most interest. It is responsible for the activity of nitronates as 1,3-dipoles in [3+ 2]-cycloaddition reactions. This is the most important aspect of the reactivity of nitronates determining the significance of these compounds in organic synthesis (see e.g., Ref. 267). In addition, this structure suggests that nitronates can show both, O -nucleophilic properties, that is, react at the oxygen atom with electrophiles, and a-C-electrophilic properties, that is, add nucleophiles at the a-carbon atom. 

The electrophilic properties of molecules were derived from 31P NMR chemical shifts9 produced by electrophilic solvents on triethylphosphine oxide as equilibrium 2 illustrates. 

This suggests that the effect of the solvent on the oxidation process of ferrocene is essentially dependent on the electrophilic properties of the solvent. 

Some examples will be seen in later sections of carcinogens that seem not to require metabolic activation to electrophiles, and which do not possess significant electrophilic properties themselves these agents appear not to be involved in the initial DNA-damaging event, but rather at later stages of the neoplastic process. 

Due to its electrophilic properties the OH° reacts at the position with the highest electron density of the target molecule. Detailed information can be found in von Sonntag (1996), which gives a good overview of the degradation mechanism of aromatics by OH° in water. Buxton et al. (1988) showed that the reaction rate constants for hydroxyl radicals and aromatic compounds are close to the diffusion limit. 

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