3- Chloro-2-methylpropene, alkylation with

Fluoronitroso compounds can be prepared by the simultaneous addition of F and NO to alkene double bonds by the use of either nitrosyl fluoridc317 -,1 9--,22-329 342 344 or a mixture of dinitrogen tetroxide and potassium fluoride.320 The nitrosofluorination reactions of hexa-fluoropropene, perfluoro(2-methylpropene) and perfluorocyclobutene by these two different methods are summarized in Table 27. Additionally, the reactions of nitrosyl fluoride with chloro-trifluoroethene,319 with alkyl perfluorovinyl ethers,317 and with perfluoro(2-methylacryloyl fluoride)344 are listed. 

El eliminations begin with the same uni molecular dissociation we saw in the Sfsjl reaction, but the dissociation is followed by loss of H+ from the adjacent carbon rather than by substitution. In fact, the El and SN1 reactions normally occur together whenever an alkyl halide is treated in a protic solvent with a non-basic nucleophile. Thus, the best El substrates are also the best SN1 substrates, and mixtures of substitution and elimination products are usually obtained. For example, when 2-chloro-2-methylpropane is warmed to 65 °C in 80% aqueous ethanol, a 64 36 mixture of 2-methyl-2-propanol (Sjql) and 2-methylpropene (El) results. 

The second point to explore involves carbocation stability. 2-Methylpropene might react with H+ to form a carbocation having three alkyl substituents (a tertiary ion, 3°), or it might react to form a carbocation having one alkyl substituent (a primary ion, 1°). Since the tertiary alkyl chloride, 2-chloro-2-methylpropane, is the only product observed, formation of the tertiary cation is evidently favored over formation of the primary cation. Thermodynamic measurements show that, indeed, the stability of carbocations increases with increasing substitution so that the stability order is tertiary > secondary > primary > methyl. 

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