Haloalkanes and Haloarene

Out of o-and p-dibromobenzene which one has a higher melting point and why?

The melting point of p-dibromobenzene is higher than that of the other two compounds. This is due to the symmetry of p-dibromobenzene, which allows the molecule to fit into the crystal lattice more easily. As a result, breaking the bonds between the molecules demands a higher temperature, resulting in a higher melting point.

Aryl chlorides and bromides can be easily prepared by electrophilic substitution of arenes with chlorine and bromine respectively in the presence of Lewis acid catalysts. But why does the preparation of aryl iodides require the presence of an oxidising agent?

In nature, iodination reactions are reversible. The HI produced during iodination is eliminated by oxidation in order to carry out the reaction in the forward direction. The oxidising agent HIO₄ is used. In nature, iodination reactions are reversible. The HI produced during iodination is eliminated by oxidation in order to carry out the reaction in the forward direction. The oxidising agent HIO₄ is used.

Which of the compounds will react faster in S_N1 reaction with the “OH” ion?

CH₃-CH₂-Cl or C₆H₅-CH₂-Cl

In the rate-determining phase of the S_N1 reaction, a carbocation intermediate is initially generated. The benzyl carbocation is resonance stabilised in benzyl chloride.

In the case of ethyl chloride or chloroethane, however, the CH₃CH₂⁺carbocation can only have a hyper-conjugation effect. It is less stable in comparison. As a result, in the S_N1 reaction, benzyl chloride reacts faster with the OH ion than ethyl chloride.

Why does iodoform have appreciable antiseptic properties?

The antiseptic qualities of iodoform (CHI₃) are attributable to iodine, which is produced when the substance comes into contact with the skin. When Iodoform comes into touch with skin, it releases I₂. Iodine’s antiseptic properties are attributable to the liberation of I₂, not iodoform itself.

Why can aryl halides not be prepared by reaction of phenol with HCl in the presence of ZnCl₂?

When an alkyl halide is formed, a carbocation is formed, which then interacts with HCl to generate an alkyl halide.

However, in order for aryl halide to react with HCl in the presence of ZnCl₂, phenyl carbocation formation must occur, which is impossible because it is a highly unstable structure that never occurs in its free state. As a result, no aryl halide is generated.