Reactions Involving Carbenes and Nitrenes

Carbenes can be classed with carbanions, carbocations, and carbon-centered radicals as among the fundamental intermediates in the reactions of carbon compounds. Carbenes are neutral, divalent derivatives of carbon. Depending on whether 

As would be expected from the electron-deficient nature of these species, they are highly reactive. 

Under some circumstances, the question arises as to whether the carbene has a finite lifetime, and in some cases there is evidence that a completely free carbene structure is never attained. When reaction appears to involve a species that reacts as expected for a carbene but must still be at least partially bound to other atoms, the term carbenoid is applied. Some reactions which involve carbene-like processes involve transition metal ions. In many of these reactions, the divalent carbene is bound to the transition metal. Some compounds of this type are stable whereas others exist only as transient intermediates. 

Carbenes and carbenoids can add to double bonds to form cyclopropanes or insert into C—H bonds. These reactions have low activation energies when the intermediate is a free carbene. When this is the case, the reactions are inherently nonselective. The course of intramolecular reactions is frequently controlled by the proximity of the reacting groups.  

Nitrenes are neutral, monovalent nitrogen analogs of carbenes. The term nitrenoid is applied to nitrene-like intermediates which transfer a monosubstituted nitrogen fragment. 

As would be expected from their electron-deficient nature, carbenes are highly reactive. Carbenes can be generated by a-elimination reactions. 

CHAPTER 10 REACTIONS INVOLVING CARBOCATIONS, CARBENES, AND RADICALS AS REACTIVE INTERMEDIATES 

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Fragmentation Reactions Reactions Involving Carbenes and Nitrenes... 

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