Question

C-Cl bond in methyl chloride compared to C-Cl bond in chlorobenzene is

• A. Longer and stronger
• B. Shorter and stronger
• C. Shorter and weaker
• D. Longer and weaker

Hint:

Remember these two key factors when comparing bonds to a benzene ring with bonds to a simple alkyl group: 1. \textbf{Hybridization:} A bond to an sp\(^2\) carbon is shorter and stronger than a bond to an sp\(^3\) carbon. 2. \textbf{Resonance:} Resonance can introduce partial double bond character, which shortens and strengthens the bond. Both factors work in the same direction for chlorobenzene, making its C-Cl bond shorter and stronger.

Answer 1

The Correct Option is D

Step 1: Analyze the bonding in methyl chloride (CH\(_3\)Cl).
In methyl chloride, the chlorine atom is bonded to a carbon atom that is sp\(^3\) hybridized. The C-Cl bond is a pure single (\(\sigma\)) bond.
Step 2: Analyze the bonding in chlorobenzene (C\(_6\)H\(_5\)Cl).
In chlorobenzene, the chlorine atom is bonded to a carbon atom that is part of the benzene ring. This carbon atom is sp\(^2\) hybridized. Furthermore, the lone pairs of electrons on the chlorine atom can participate in resonance with the \(\pi\)-electron system of the benzene ring. This resonance delocalization gives the C-Cl bond a partial double bond character.
Step 3: Compare the bond length and bond strength.
Bond Length:

• A single bond is longer than a double bond.
• The C(sp\(^2\))-Cl bond in chlorobenzene has partial double bond character, making it shorter than the C(sp\(^3\))-Cl single bond in methyl chloride.
• Also, an sp\(^2\) hybrid orbital has more s-character (33.3%) than an sp\(^3\) hybrid orbital (25%). More s-character leads to shorter and stronger bonds.

Therefore, the C-Cl bond in methyl chloride is longer.
Bond Strength:

• A double bond is stronger than a single bond.
• Because the C-Cl bond in chlorobenzene has partial double bond character, it is stronger than the pure single C-Cl bond in methyl chloride.

Therefore, the C-Cl bond in methyl chloride is weaker.
Step 4: Final Answer.
Combining the two comparisons, the C-Cl bond in methyl chloride is longer and weaker than the C-Cl bond in chlorobenzene.