SolutionsIsomerization
1. Order the carbocations
Arrange from least to most unstable: CH3CH2+, (CH3)3C+, CH3+ and (CH3)2CH+.
(CH3)3C+ (tertiary) < (CH3)2CH+ (secondary) < CH3CH2+ (primary) < CH3+ (methyl).
2. Isomerization product
What product is obtained by isomerizing butane with AlCl3? And pentane?
Butane gives 2-methylpropane (isobutane) and pentane gives 2-methylbutane (isopentane).
The reaction leads to the branched isomers, through the most substituted, least unstable carbocation.
3. Type of cleavage
What type of bond cleavage takes place in isomerization with a Lewis acid? How does it differ from halogenation?
Heterolytic cleavage: AlCl3 removes a hydride (H−) and a carbocation is formed. In halogenation the cleavage is homolytic and the intermediates are radicals.
4. What is it for?
Why is it industrially useful to turn linear alkanes into branched ones?
Because branched alkanes have a much higher octane number and improve the quality of gasoline.