Video Transcript
This equation describes the reaction that happens in the presence of heat and ultraviolet light. The X-term represents an unidentified molecule. What is the structure of this unidentified molecule?
The organic reactant shown in this reaction equation is benzene, an aromatic hydrocarbon. The circle in the skeletal structure represents the delocalized electrons in the ring. We can also represent a molecule of benzene with the skeletal structure that shows alternating single and double bonds in the ring. When benzene is reacted with a halogen, such as diatomic chlorine, in the presence of ultraviolet light and heat, a halogen addition reaction occurs. In a halogen addition reaction, a molecule combines with one or more halogen molecules to form a larger molecule without any byproducts forming.
To answer this question, we need to determine the structure of the larger molecule represented in the equation by the term X. During the halogen addition involving a benzene ring, one of the carbon-carbon double bonds in the ring is broken along with the bond between the two halogen atoms, in this case the two chlorine atoms. This loss of bonds allows for the formation of two new carbon-chlorine single bonds. As three equivalent of chlorine are used in this reaction, the reaction can occur with each of the double bonds in the ring. This produces a product in which the ring structure no longer contains any double bonds. In addition, each of the carbon atoms in the ring is bonded to one chlorine atom and one hydrogen atom.
We can see that the structure that we have drawn matches the one shown in answer choice (A). Therefore, the structure of the unidentified molecule, the product of the reaction of benzene with three equivalents of chlorine in the presence of ultraviolet light and heat, is the structure shown in answer choice (A).
