Follow US:

Practice English Speaking&Listening with: Video Answer to Q11.66

Normal
(0)
Difficulty: 0

The negatively charged oxygen compound

tertiary-butoxide,

is the electron donor and is either a nucleophile or base.

The alkyl halide is the electrophile or electron acceptor

The electrophilic carbon is tertiary

The electron donor, t-butoxide is a bulky sterically hindered strong base

that is a very poor nucleophile

The solvent tertiary-butanol.

However, the formation of a carbocation is not likely

since a strong base is present and a fast exothermic E2 reaction

will dominate over a slow endothermic SN1/E1 reaction

Looking at the substitution/elimination chart for alkyl halides

We see t-butoxide is a poor nucleophile and a bulky sterically hindered strong base

that is attacking a sterically hindered tertiary alkyl halide.

An E2 reaction will occur

The dominate reaction will be an E2 reaction because

the bulky base is sterically hindered from reaching the electrophilic carbon.

The SN2 product will not form in this reaction.

The E2 reaction can occur with the at secondary beta carbon

to product 2-methylbut-2-ene

or at the primary beta carbon to produce 2- methylbut-1-ene

Looking at the reaction coordinate potential energy diagram

we see that there is greater steric interaction between the base and the substrate in the transition state

when the bulky base is abstracting a secondary proton

compared with abstracting a primary proton.

The energy of the transition state

that produces the more thermodynamically stable alkene

is greater than the transition state that produces the less stable alkene.

A larger activation energy decreases the rate of reaction

and causes the more stable alkene to become a minor product.

Thus, the major product of this reaction is the less stable alkene 2-methylbut-1-ene

or the Hofmann product.

The Description of Video Answer to Q11.66