Question

Answer the following:
Give two examples which prove that benzene behaves differently than aliphatic unsaturated hydrocarbons.

Answer 1

Hint: Benzene behaves like a saturated hydrocarbon because of its aromaticity. In benzene, all the six pi electrons of the three double bonds are delocalized completely to form one molecular orbital with lowest energy and which also surrounds all the carbon atoms.

Complete answer:Benzene behaves differently than aliphatic unsaturated hydrocarbons because it is hydrogenated in harsh conditions.
${C_6}{H_6} + {H_2} \to {C_6}{H_{12}}$
It behaves like a saturated compound as it usually requires harsher conditions for those reactions to take place. Saturated compounds are considered to be relatively less reactive. For example, alkanes can decolorize bromine water but some conditions need to be met. Consider the following example of cyclohexane:
${C_6}{H_{12}} + B{r_2} \to {\text{no reaction}}$
${C_6}{H_{12}} + B{r_2} \to {C_6}{H_{11}}Br + HBr$
For this reaction, the condition is UV.
Let us consider one more case. Alkenes can decolorize bromine water readily. This happens even in the dark. The reaction of ethene is given below:
${C_2}{H_4} + B{r_2} \to {C_2}{H_4}B{r_2}$
But, benzene requires a catalyst.
${C_6}{H_6} + B{r_2} \to {C_6}{H_5}Br + HBr$
For this reaction to take place, a catalyst is required.

Note:
Benzene is usually rather unreactive towards addition reactions compared to alkenes. This is because of the valence electrons that are shared equally by all the six carbon atoms. These electrons are called delocalized electrons. The delocalized electrons are present above and below the plane of the benzene ring. This increases the stability of benzene. Benzene is used in the manufacturing of plastics, synthetic fibers, resins, dyes, pesticides, drugs, industrial solvents, rubber lubricants, paints, glues, thinners, detergents, gasoline and other fuels.