Question

In the presence of ${\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$, 2-methylpropene oxide undergoes chain-growth polymerization such that nucleophilic attack occurs at the more substituted end of the epoxide. Draw a stepwise mechanism for this process, and explain this regioselectivity.

Short answer

Answer

Mechanism of the reaction

Step-by-step solution

2-methylpropene oxide

2-methylpropeneoxide is an epoxide ring consisting of two methyl groups at the second carbon atom. This organic compound is a colorless liquid and is used in the synthesis of polyurethane plastic materials.

About chain-growth polymerization

The step-by-step addition of monomers (unsaturated) to active sites to produce a giant molecule of polymers is called chain-growth polymerization.

Initiation, propagation, and termination are the compulsory steps involved in chain-growth polymerization.

About the mechanism

The oxygen atom of the epoxide ring abstracts the proton and it becomes OH. Another water molecule is added to this species which leads to the development of a positive charge on the oxygen atom.

Another water molecule is added that abstracts proton. This step is repeated several times. The mechanism is given below.

Mechanism of the reaction

Regioselectivity

The nucleophilic attack usually occurs at the more substituted carbon atom. So when the ring-opening takes place, a nucleophilic attack happens in the carbon atom having more ability to accept δ+ in its transition state.

Because it gets stabilized and permits faster reaction, it is possible in , a group of a transition state that bears δ+ carbon.