Vinyl cation mesomeric

Allenyl cations 1 are a stabilized form of vinyl cations1-3 in which the /1-carbon atom of the vinylic structure is part of the substituent which effects the stabilization of the ion via its electron-donating ability. This leads to a resonance hybrid having formally the alkynyl cation structure 2. Allenyl cations should be distinguished from the allenyl substituted carbenium ions 3 formulated as the mesomeric structures of the vinyl cations 4 (dienyl cations) stabilized by an w-vinyl group (equation 1). 

Both the butatrienyl halides 54a and 54b gave the alkyne (56) as the sole product in 97-100% yield41. The kinetics described above fit the mechanistic sequence shown in equation 20 for the formation of the product 56. The mesomeric butatrienyl vinyl cation 55... 

Propargyl and Allenylmethyl Cations (Mesomeric Vinyl Cations)... 

In contrast to vinyl cations, propargyl cations 117a exist in mesomeric allenyl forms 117b, which can serve as models for vinyl cations. 

In the early 1980s, Siehl and co-workers319,320 prepared two allenylmethyl cations 120 and 121 using the codeposition technique developed by Saunders et al.49 The cations thus prepared also exhibit extensive mesomeric vinyl cation character. 

N of nitrogen belongs to the set IB. The synthons 1 to n are unstable except of one mesomeric structure of the synthon n

The nitrogen atom attached to the vinyl group lowers the electron density in the vinyl group by its inductive effect, but the mesomeric effect of the nitrogen electron pair overwhelms the inductive effect so that a conjugated r-electron system is formed. Therefore, NVK can be polymerized readily by cationic initiators. Anionic polymerization is not possible with... 

In the case of a radical cation, the mesomeric effects can involve the charge and/or the radical as is the case in Figure 9.13. A vinyl ether ionized by electron ionization is... 

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