Q29P - Organic Chemistry (Mcmurry)

Question

Question: When methyl vinyl ether reacts with a strong acid, the proton adds to

C2 exclusively, instead of C1 or the oxygen atom. Draw the three protonated

forms of methyl vinyl ether and explain this observation

Step-by-Step Solution

Answer

Answer

Among the different carbocations, the secondary carbocation is stable and can undergo resonance.

Step 1: Electrophilic addition reactions

Electrophilic addition reactions involve the attack of the pi electrons of the double bond on the of the acid to generate a carbocation. One of the carbons in C=C gets connected to the hydrogen while the other gets a positive charge.

Step 2: Proposing the mechanism for the reaction

In methyl vinyl ether, there are three possible positions of protonation.

If the protonation happens , the carbocation formed is a primary carbocation and has less stability. The carbocation can be given as:

 

Protonation at C1

If the protonation happens at, the carbocation formed is a secondary carbocation, whose stability is more than the primary carbocation. The secondary carbocation formed can be given as:

Secondary carbocation

If the protonation happens at oxygen, the carbocation formed can be given as:

Carbocation formed when protonation happens at oxygen

Among the different carbocations, the secondary carbocation is stable and can undergo resonance and attain stability.

Resonance of secondary carbocation