Electron-rich reagents

Electron rich reagents can displace the metal IVb hydride and in the case of optically active complexes this reaction proceeds with retention of configuration. 

Alkynes are electron-rich reagents. The triple bond acts as a nucleophile, and attacks the electrophile. Therefore, alkynes undergo electrophilic... 

In the case of the electron rich reagents, no addition products were observed, either under catalytic or stoichiometric conditions. In all cases, no evidence of incorporation was discerned from IR analysis. In addition to unidentifiable materials (in the ethyl ethynyl ether case), substantial side reaction could be recognized. 

Photoinduced electron transfer [1, 2] represents the simplest way of achieving charge reversal in chemical reagents. As shown in Eq. 1, an electron-rich reagent D can interact... 

To envision how chemical reaction arises from differences in polarity it is argued [96] that, since unlike charges attract, electron-rich sites in the functional groups of one molecule react with the electron-poor sites in the functional groups of another molecule. Bonds are made when the electron-rich reagent donates a pair of electrons to the electron-poor reagent. The movement of bonding electron pairs is followed by the use of curly arrows. The formalism is illustrated by some chemical reactions ... 

Elementary chlorine, bromine, and iodine dissolve in many organic solvents, and the variations in the colors among the iodine solutions in various solvents have been a matter of interest to many workers. (Both bromine solutions and solutions of iodine monochloride show analogous variations, but the effect for iodine is by far the most striking.) In completely nonbasic solvents (for example, CCU and CS2) iodine appears violet, the same color as its vapor but as the basicity of the solvent increases, the iodine color shifts toward orange or brown, presumably because the electronic excitation responsible for the iodine color is made more difficult by approach of electron-rich reagents. As the basicity of the solvent increases, the iodine-to-iodine bond weakens in the organic base, pyridine (reaction c, below), many of the I—I bonds are broken, wrhereas... 

Polar reactions take piace between electron rich reagents (mideophtles Lewis bases) snd electron pctor reagents felectropliilesdjewis acids). These reactions are betcrolytic processes and involve species with an even num> her of electrons. Bonds are made when a nucleojAile donates an elecuon pair to an electrophile bonds are broken when one product leaves with an elecmm patr. 

What kind of reactions do alkyl halides undergo The characteristic reactions of alkyl halides are substitution and elimination. Because alkyl halides contain an electrophilic carbon, they react with electron-rich reagents— Lewis bases (nucleophiles) and Brpnsted—Lowry bases. 

In both reactions RX acts as an electrophile, reacting with an electron-rich reagent. 

If you know the product of a reaction, usually it is not too difficult to determine whether an electron-rich reagent is acting as a base or as a nucleophile. Predicting the course of a reaction can be a more difficult task. However, as you work through a number of examples and problems, you will start to develop a feel for this as well. 

Basic, electron-rich reagents are called nucleophilic reagents (from the Greek, nucleus-loving). The typical reaction of alkyl halides is nucleophilic substitution ... 

At the outset, one might have expected that Ceo would be relatively chemically inert its compact shape and high symmetry suggest that to attack it chemically may be difficult. However, it reacts readily with appropriate electron-rich reagents, and specific and selective additions are possible. 

We note that Coo chemically inert (14) but reacts readily with electron-rich reagents. Its double-bond reactivity resembles that of very electron-poor arenes and alk-enes. It follows that much of the reaction chemistry of these types of carbon-carbon double bonds might be successfully applied to Cgo-... 

Nucleophilic addition reactions are mainly of technical interest in the context of further reactions at C=0 groups present in aldehydes or ketones. The electronic nature of a carbonyl group is characterized by the greater electronegativity of the oxygen atom compared to the carbon atom. Thus, the carbon atom is the preferred place of nucleophilic attack, that is, of reaction with an electron-rich reagent. Scheme 2.2.12 gives as an example the technically important cyanohydrin reaction. Other important nucleophilic additions are the reaction of carbonyl compounds with alcohols and water, bisulfite and metal hydrides. 

We ve now studied three of the four general kinds of carbonyl-group reactions and have seen two general kinds of behavior. In nucleophilic addition and nucleophilic acyl substitution reactions, a carbonyl compound behaves as an electrophile when an electron-rich reagent adds to it. In a-substitution reactions, however, a carbonyl compound behaves as a nucleophile when it is converted into its enol or enolate ion. In the carbonyl condensation reaction that we ll study in this chapter, the carbonyl compound behaves both as an electrophile and as a nucleophile. 

Nucleophile - Nucleophiles or Nucleophilic reagents are basic, electron-rich reagents. Negative ions and chemical groups can be nucleophiles, in addition to neutral compounds such as ammonia and water. Both ammonia and water molecules contain a pair of unshared electrons. 

Scheme 8.1 Catalytic dediazotation of diazoalkanes and accompanying reactions with electron-rich reagents.

This reaction could be reproduced with several carbocyclic alkenes 401 with the same electron-rich reagent, but better results (as fat as selectivity was concerned) were obtained with cobaltocene reduced with potassium, CP2C0/K (Figure 82)." ... 

In the heterolytic cleavage of a bond, the electron pair lies with one of the fragments, which becomes electron-rich, while the other fragment becomes electron-deficient. An electron-rich reagent gets attracted to the center of the... 

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