Electrophilic carbon, addition with Subject

Compounds with a low HOMO and LUMO (Figure 5.5b) tend to be stable to selfreaction but are chemically reactive as Lewis acids and electrophiles. The lower the LUMO, the more reactive. Carbocations, with LUMO near a, are the most powerful acids and electrophiles, followed by boranes and some metal cations. Where the LUMO is the a of an H—X bond, the compound will be a Lowry-Bronsted acid (proton donor). A Lowry-Bronsted acid is a special case of a Lewis acid. Where the LUMO is the cr of a C—X bond, the compound will tend to be subject to nucleophilic substitution. Alkyl halides and other carbon compounds with good leaving groups are examples of this group. Where the LUMO is the n of a C=X bond, the compound will tend to be subject to nucleophilic addition. Carbonyls, imines, and nitriles exemplify this group. 

The -allenyl/propargyl platinum cations generally exhibit electrophilicity at the central carbon. The unsubstituted rj -allenyl/propargyl species is particularly reactive and is subject to addition to a wide variety of nncleophiles (see Nucleophile). The reactions of the -allenyl/propargyl species with alcohol,... 

Enolates react with other carbonyl groups at the electrophilic carbonyl carbon. These reactions are more complicated because the initial addition adduct goes on to form different products depending on the structure of the carbonyl group. These reactions form the subject of Chapter 24. 

The central carbon atom, flanked by two nitrogen atoms, is electrophilic and thus subject to nucleophilic attack by a variety of reagents. The most well-known reactions are those between carbodiimides and acids. For example, carbodiimides will undergo addition reactions with a variety of weak acids ... 

The diminished electron density makes the carbon-carbon It bond less reactive toward an electrophile. However, for the same reason, the P-carbon atom is electrophilic and can react with nucleophiles. Addition reactions to conjugated systems are the subject of the next section. 

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