Carbocations allyl

Conjugare is a Latin verb meaning to link or yoke together and allylic carbocations allylic free radicals and conjugated dienes are all examples of conjugated systems In this chapter we 11 see how conjugation permits two functional units within a molecule to display a kind of reactivity that is qualitatively different from that of either unit alone... 

The carbocation is stabilized by delocalization of the tt electrons of the double bond and the positive charge is shared by the two CH2 groups Substituted analogs of allyl cation are called allylic carbocations Allyl group (Sections 5 1 10 1) The group... 

Allylic carbocation Allylic free radical Conjugated diene... 

Allyl bromide, CH2=CHCH2Br, will react faster than CH3CH2CH2Br because ionization of the C-Br bond gives the more stable carbocation (allylic versus primary). 

Triphenylmethyl Benzyl carbocation Allyl carbocation carbocation... 

This is called allyl type resonance because it can be drawn for allylic carbocations, allylic carb-anions, and allylic radicals. 

An adjacent C=C n system stabilizes a carbocation allylic and benzylic carbocations... 

Any structural effect which reduces the electron deficiency at the tricoordinate carbon will have the effect of stabilizing the carbocation. Allyl cations are stabilized by delocalization involving the adjacent double bond. 

Allylic carbocations, like allylic radicals (Section 8.6), have a double bond next to the electron-deficient carbon. The allyl cation is the simplest allylic carbocation. Because the allyl cation has only one substituent on the carbon bearing the positive charge, it is a primary allylic carbocation. Allylic carbocations are considerably more stable than comparably substituted alkyl carbocations because delocalization is associated with the resonance interaction between the positively charged carbon and the adjacent tt bond. The allyl cation, for example, can be represented as a hybrid of two equivalent contributing structures. The result is that the positive charge appears only on carbons 1 and 3, as shown in the accompanying electrostatic potential map. 

However, like carbocations, allylic and benzyllic carbanions are lower than ordinary carbanions due to resonance stabilization. 

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