Chapter 9, Problem 32P

Diphenylacetylene can be synthesized by the double dehydrohalogenationof $\text{1,2-dibromo-1,2-diphenylethene}$. The sequence starting from $\text{(E)-1,2-diphenylethene}$ consists ofbromination to give the dibromide, followed by dehydrohalogenation to give a vinylicbromide, then a second dehydrohalogenation to give diphenylacetylene.

(a) What is the structure, including stereochemistry, of the vinylic bromide?

(b) If the sequence starts with $\text{(Z)-1,2-dibromo-1,2-diphenylethene}$, what is (are) thestructure(s) of the intermediate dibromide(s)? What is the structure of the vinylicbromide?