Question

The compound with molecular formula C$_6$H$_6$, which gives only one monobromo derivative and takes up four moles of hydrogen per mole for complete hydrogenation has ___ $\pi$ electrons.

Hint:

Aromatic compounds like benzene (C$_6$H$_6$) have a conjugated system of $\pi$-electrons that satisfy Hückel's rule, which states that aromatic compounds have 4n + 2 $\pi$-electrons (where n is a whole number).

Answer 1

Correct Answer: 6

The compound with the molecular formula C$_6$H$_6$ is benzene, which is a well-known aromatic compound. Benzene has a planar ring structure with alternating single and double bonds between the carbon atoms, forming a conjugated system. Each carbon-carbon double bond contributes 2 $\pi$-electrons. Since benzene has 6 carbon atoms, and all of them participate in the conjugation, the total number of $\pi$-electrons in benzene is 6. Thus, the answer is: $$\text{The number of } \pi \text{ electrons} = 6$$