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 molecular formula C\(_6\)H\(_6\) is benzene. Benzene's structure involves a ring of six carbon atoms with alternating single and double bonds, indicating delocalized π-electrons across the ring. In benzene, all the carbon-carbon bonds are of equal length due to resonance, resulting in a stable compound exhibiting aromaticity.

To determine the number of π-electrons, consider the following:

1. Benzene's structure: C\(_6\)H\(_6\) is a cyclic compound with alternating double bonds, contributing π-electrons from the double bonds.
2. Each double bond consists of π-electrons shared between two carbon atoms. Benzene contains three double bonds.
3. Each double bond contributes two π-electrons, hence in benzene, there are 3 double bonds × 2 π-electrons/double bond = 6 π-electrons.

Since the problem states that benzene yields only one monobromo derivative, this indicates all hydrogen atoms in the ring are equivalent, further confirming its structure as benzene.

Upon complete hydrogenation, benzene takes up 4 moles of hydrogen, converting each double bond into a single bond, consistent with the presence of three double bonds.

The computed number of π-electrons is 6, which fits within the specified range of 6 to 6.

Answer 2

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: \[ \text{The number of } \pi \text{ electrons} = 6 \]