Draw at least five isomeric structures that have the molecular formula C6H6. Note that all are highly unsaturated or contain small, strained rings.
The Correct Answer and Explanation is:
The molecular formula C6H6 corresponds to compounds with six carbon atoms and six hydrogen atoms, which is characteristic of benzene and its derivatives. However, because the compound is highly unsaturated, it suggests that it contains conjugated double bonds, making it an aromatic hydrocarbon or a compound with strained rings. Here are five possible isomeric structures for C6H6:
- Benzene (C6H6):
The simplest and most well-known structure is benzene, a six-membered ring with alternating single and double bonds between carbon atoms. Each carbon is bonded to one hydrogen atom. The structure is highly stable due to resonance, where the electrons are delocalized over the six carbon atoms. - Cyclohexa-1,3,5-triene (also called benzene):
This is just another way of describing benzene itself, as it follows the same alternating double bond structure. - 1,3-Cyclohexadiene:
This is a six-membered ring with two double bonds at positions 1 and 3. This compound is unsaturated, and unlike benzene, it does not have the resonance stabilization, making it less stable. - 1,2-Cyclohexadiene:
Similar to 1,3-cyclohexadiene, this compound also has two double bonds but positioned between carbons 1 and 2. Again, it is unsaturated and lacks the resonance stabilization seen in benzene. - Cyclopropene:
This is a three-membered ring (cyclopropene) with two carbon atoms doubly bonded. A very strained and highly reactive compound that can form resonance with more stable molecules like benzene under some conditions. - Cyclobutadiene:
Another highly strained structure is cyclobutadiene, a four-membered ring with two double bonds. Like cyclopropene, it’s highly reactive due to ring strain.
Explanation:
The molecular formula C6H6 represents compounds with six carbon atoms, typically forming highly unsaturated molecules. Benzene is the most stable isomer because of its delocalized electrons in a conjugated ring system, giving it aromatic stability. The other structures are variations of cyclohexadiene and strained ring compounds. The alternating double bonds in benzene and cyclohexadiene are key features of these isomers, but their stability decreases without the resonance effect found in benzene. Each of these molecules would undergo reactions typical of unsaturated hydrocarbons, such as addition reactions and nucleophilic attacks. The strain in smaller rings, like cyclobutadiene and cyclopropene, makes these compounds highly reactive.
