Dimerization of 2-methylpropene

The two dimers of 2 methylpropene shown in the equation can be converted to 2 2 4 trimethylpentane (known by its common name isooctane) for use as a gasoline additive Can you suggest a method for this conversion ... 

FIGURE 6 16 Mechanism of acid catalyzed dimerization of 2 methylpropene... 

Hydroboration of 1-Methylcyclopentene 248 6.10 Acid-Catalyzed Dimerization of 2-Methylpropene 262... 

Scheme 6.33. A representation of the path of the dimerization of 2-methylpropene [isobutylene (CH3)2C=CH2] to form a carbocation that loses a proton (H ) to give the two alkenes, (path a) 2,4,4-trimethyl-2-pentene [(CH3)3CH=C(CHj)2] and (path b) 2,4,4-trunethyl-l-pentene [(CH3)3CCH2C(CH3)=CH2].The catalytic (Pt.Ni.etc.) reduction (hydrogenation) of the alkene mixture yields 2,2,4-trimethylpentane [isooctane, (CH3)3CCH2CH(CH3)2].

The two dimers of 2-methylpropene tend to react further with the starting alkene. For example, when 2-methylpropene is treated with strong acid under more concentrated conditions, trimers, tetramers, pentamers, and so forth, are formed by repeated electrophilic attack... 

A mixture of 2,4,4-trimethyl-l-pentene and 2,4,4-trimethyl-2-pentene is obtained in the commercial dimerization of 2-methylpropene. Hydrogenation of the mixture gives a single product. Draw the strucmres of the alkenes and the product. Explain why a single product forms. 

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