Chapter 7, Problem 40AP

Consider the following proposed structures for benzene, each of which is consistent with the molecular formula ${\text{C}}_6{\text{H}}_6.$

(iv) ${\text{CH}}_3-\text{C}\equiv \text{C}-\text{C}\equiv \text{C}-{\text{CH}}_3$

(v) ${\text{CH}}_2=\text{CH}-\equiv \text{C}-\text{CH}={\text{CH}}_2$

When benzene reacts with chlorine to give ${\text{C}}_6{\text{H}}_5\text{Cl,}$

1. only one isomer of that compound forms. Which of the five proposed structures for benzene are consistent with this observation?
When ${\text{C}}_6{\text{H}}_5\text{Cl}$ reacts further with chlorine to give ${\text{C}}_6{\text{H}}_4{\text{Cl}}_2,$ exactly three isomers of the latter compound form. Which of the five proposed structures for benzene are consistent with this observation?