Consider the structure of cis-1, 2-divinylcyclopropane:

This compound is stable at low temperature but rearranges at room temperature to produce 1, 4-cycloheptadiene.

(a) Draw a mechanism for this transformation.

(b) Using brackets and numbers, identify the type of sigmatropic rearrangement taking place in this case.

(c) This reaction proceeds to completion, which means that the concentration of the reactant is insignificant once the equilibrium has been established. Explain why this reaction proceeds to completion.