What is the expected product for the following reaction? t-BuOK H3C\nCH3 H3C Br t-BuOH heat The following compound: H3C CH3 CH3 The following compound: H3C CH3 H3C O The following compound: ? H3C CH3 CH3 The following compound: H3C CH3 H3C OH The following compound: H3C CH3
The Correct Answer and Explanation is:
The given reaction involves potassium tert-butoxide (t-BuOK), which is a strong and bulky base, along with heat. This setup suggests an elimination reaction, specifically an E2 mechanism.
Expected Product
The correct product for this reaction is 2-methylpropene (isobutene).
Explanation
This reaction follows an E2 elimination mechanism, which occurs in a single concerted step where the base abstracts a proton from the β-carbon (carbon adjacent to the carbon bonded to bromine), leading to the formation of a double bond and the departure of bromine as a leaving group.
- Base Strength and Bulky Nature
- Potassium tert-butoxide is a strong and bulky base, which favors elimination over substitution. It preferentially removes the proton from the most accessible β-carbon, favoring the formation of a double bond.
- Formation of the Alkene
- The substrate contains a tert-butyl bromide functional group. The bulky base abstracts a proton from the carbon adjacent to the bromine. As a result, the bromine leaves, and a double bond is formed between the two carbons, generating 2-methylpropene.
- Regioselectivity and Stability
- The most substituted alkene forms preferentially due to Zaitsev’s Rule, which states that elimination favors the production of the more stable, highly substituted alkene. Since the product contains a tertiary alkene, it is the most thermodynamically stable configuration.
- Reaction Conditions and Favorability
- The presence of heat reinforces elimination as the dominant pathway. E2 reactions occur best under high-temperature conditions, leading to rapid and irreversible formation of the alkene.
Final Product
The resulting compound is 2-methylpropene (H2C=C(CH3)2), which is the expected product based on the provided reaction conditions.
