The percentage compositions of the mixture of isomeric methylbutenes obtained from 2-bromo-2-methylbutane with potassium hydroxide and potassium tert-butoxide needs to be calculated. Concept Introduction: In the dehydrogenation reaction of 2-bromo-2-methyl butane, mixture of products is formed only if the halogen is asymmetrically located on the carbon skeleton. 2-bromo-2-methyl butane results in the production of 2-methyl-2-butene and 2-methyl-1-butene on reaction with a strong base that is KOH. The elimination reaction is irreversible thus, the ratio of products formed are defined by the relative rates of the formation of two products. The rate of the formation is determined by the relative free energies of the 2-transition states rather than the free energies of the products itself. The product formed in higher yield is more substituted alkene which is 2-methyl-2-butene but this is not the case when transition state is considered, due to stearic interactions between the methyl group, beta carbon atom and the base which is not there in the transition state of 2-methyl-1-butene. Thus, thermodynamically less table product is formed that is 2-methyl-1-butene. The percentage composition of two products varies if different bases are used.

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Chapter 10.2, Problem 17E

Interpretation Introduction

Interpretation: The percentage compositions of the mixture of isomeric methylbutenes obtained from 2-bromo-2-methylbutane with potassium hydroxide and potassium tert-butoxide needs to be calculated.

Concept Introduction: In the dehydrogenation reaction of 2-bromo-2-methyl butane, mixture of products is formed only if the halogen is asymmetrically located on the carbon skeleton.

2-bromo-2-methyl butane results in the production of 2-methyl-2-butene and 2-methyl-1-butene on reaction with a strong base that is KOH. The elimination reaction is irreversible thus, the ratio of products formed are defined by the relative rates of the formation of two products.

The rate of the formation is determined by the relative free energies of the 2-transition states rather than the free energies of the products itself.

The product formed in higher yield is more substituted alkene which is 2-methyl-2-butene but this is not the case when transition state is considered, due to stearic interactions between the methyl group, beta carbon atom and the base which is not there in the transition state of 2-methyl-1-butene. Thus, thermodynamically less table product is formed that is 2-methyl-1-butene. The percentage composition of two products varies if different bases are used.

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