Problem 177 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

Which of the following statements is incorrect regarding benzyl chloride? [KCET 2003| (a) It gives white precipitate with alcoholic \(\mathrm{AgNO}_{3}\) (b) It is an aromatic compound with substitution in the side chain (c) It undergoes nucleophilic substitution reaction (d) It is less reactive than vinyl chloride

Step-by-Step Solution

Answer

Statement (d) is incorrect: Benzyl chloride is more reactive than vinyl chloride.

Step 1: Understand the Question

We need to find out which of the given statements about benzyl chloride is incorrect. Analyze each option carefully.

Step 2: Evaluate Statement (a)

Benzyl chloride reacts with alcoholic \(\mathrm{AgNO}_{3}\), leading to the formation of a white precipitate of silver chloride (\(\mathrm{AgCl}\)). This statement is true.

Step 3: Analyze Statement (b)

Benzyl chloride consists of a benzene ring with a \(\text{-CH}_2\text{Cl}\) side chain. It is indeed an aromatic compound with substitution in the side chain, making this statement true.

Step 4: Assess Statement (c)

Benzyl chloride can undergo a nucleophilic substitution reaction due to the presence of the reactive \(\text{C-Cl}\) bond. Therefore, this statement is true.

Step 5: Review Statement (d)

Vinyl chloride (\(\text{CH}_2=CHCl\)) involves an \(\text{sp}^2\)-hybridized carbon, making it less reactive towards nucleophilic substitution compared to the \(\text{sp}^3\)-hybridized carbon in benzyl chloride. Thus, benzyl chloride is more reactive than vinyl chloride, making this statement incorrect.

Key Concepts

Nucleophilic Substitution

Nucleophilic substitution is a type of chemical reaction where a nucleophile replaces a leaving group on a molecule. In benzyl chloride, the chlorine (Cl) atom acts as the leaving group. This is because the C-Cl bond is polar, making the carbon susceptible to attack by nucleophiles.
Nucleophiles are electron-rich species. They love to donate electrons to electron-deficient areas on other molecules. In the case of benzyl chloride, the nucleophile will attack the carbon atom bonded to the chlorine atom, resulting in the substitution of chlorine with the nucleophile.

• Example Reaction: Benzyl chloride reacts with water, where the -OH group from water acts as a nucleophile replacing the chlorine atom.
• Result: Formation of benzyl alcohol and release of chloride ion.

The reason benzyl chloride undergoes nucleophilic substitution is due to the relatively weak bond between the carbon and chlorine, which is easier to break compared to some other compounds.

Aromatic Compound

An aromatic compound is characterized by a stable ring of atoms that follows Hückel’s rule. This means it contains a planar ring with \(4n + 2\) pi electrons, where n is an integer. Benzyl chloride is an example of an aromatic compound.
Benzyl chloride features a benzene ring, which is a classic aromatic structure. Its aromatic nature is due to the delocalization of electrons across the planar ring.

• The chemical structure of benzyl chloride is: a benzene ring attached to a carbon atom that is further bonded to a chlorine atom (-CH₂Cl).
• It is often referred to as having a side chain substitution because the chlorine atom is part of the methyl group connected to the benzene ring, rather than part of the ring itself.

These structural features are crucial for various reactions, including electrophilic and nucleophilic substitutions, which are typical in aromatic chemistry.

Reactivity Comparison

The reactivity of chemical compounds is vital in understanding how they behave in various reactions. Comparing the reactivity of benzyl chloride with vinyl chloride helps in assessing their tendencies in nucleophilic substitution.
Benzyl chloride is more reactive than vinyl chloride due to its structure:

• Benzyl chloride consists of an \(sp^3\) hybridized carbon in the side chain, making it more prone to reaction since the C-Cl bond is easier to break.
• Vinyl chloride, on the other hand, has an \(sp^2\) hybridized carbon linked to the chlorine. This bond is stronger and less susceptible to nucleophilic attack compared to benzyl chloride.

Therefore, when comparing benzyl chloride to vinyl chloride, it is essential to recognize that benzyl chloride can readily participate in nucleophilic substitution reactions, making it generally more reactive.