Which of the following species is conjugated?

• A. $C_6{H}_6$ (benzene)
• B. $C_3{H}_8$ (propane)
• C. $C_2{H}_4$ (ethylene)
• D. $C_2{H}_6$ (ethane)

Answer: (A)

Verified step by step guidance

1. Understand the concept of conjugation: Conjugation occurs when p-orbitals on adjacent atoms overlap, allowing for delocalization of π electrons across multiple atoms. This typically involves alternating single and double bonds or lone pairs adjacent to double bonds.
2. Examine each species for the presence of alternating double and single bonds or continuous p-orbital overlap: For example, benzene (C\_6H\_6) has a ring structure with alternating double bonds, which allows for continuous overlap of p-orbitals.
3. Check propane (C\_3H\_8) and ethane (C\_2H\_6): Both are saturated hydrocarbons with only single bonds, so they lack the alternating double bonds necessary for conjugation.
4. Look at ethylene (C\_2H\_4): It has a double bond between two carbons but no alternating single and double bonds extending beyond that, so it is not conjugated over multiple bonds.
5. Conclude that benzene is conjugated due to its cyclic structure with alternating double bonds, which allows for delocalized π electrons, a key feature of conjugation.