Among the following compounds, which one has the shortest C–Cl bond?

Step 1: Understand bond length factors

C–Cl bond length depends on:

1. Hybridization of carbon (sp > sp² > sp³)
2. Resonance (partial double bond character)
3. Inductive effects

Step 2: Analyze each option

(a) Tertiary alkyl chloride:

• sp³ hybridized carbon
• Normal C–Cl single bond
• Bond length: ~1.78 Å

(b) Vinyl chloride ($\ce{CH2=CHCl}$):

• sp² hybridized carbon
• Higher s-character (33% vs 25%)
• Shorter, stronger bond
• Possible resonance: $\ce{CH2=CH-Cl <-> CH2+-CH=Cl-}$
• Bond length: ~1.69 Å
• Shortest ✓

(c) Methyl chloride ($\ce{CH3Cl}$):

• sp³ hybridized carbon
• Normal C–Cl single bond
• Bond length: ~1.78 Å

(d) Appears to be another alkyl chloride:

• sp³ hybridized
• Normal bond length

Step 3: Hybridization effect

Bond length order:

• sp–Cl (shortest) - if C≡C–Cl existed
• sp²–Cl (short) - vinyl chloride ✓
• sp³–Cl (longest) - alkyl chlorides

Why sp² gives shorter bond:

• More s-character (33% vs 25%)
• s-orbitals are closer to nucleus
• Tighter overlap
• Shorter, stronger bond

Answer: (b) Vinyl chloride

Key Concepts:

Hybridization and bond length:

| Hybridization | s-character | C–X bond length | Example | |---------------|-------------|-----------------|----------| | sp | 50% | Shortest | $\ce{HC≡C-Cl}$ | | sp² | 33% | Short | $\ce{CH2=CH-Cl}$ | | sp³ | 25% | Longest | $\ce{CH3-Cl}$ |

Vinyl and aryl halides:

• C–X bond has partial double bond character
• Resonance with π system
• Shorter and stronger than alkyl halides
• Less reactive toward nucleophilic substitution