Which C–X bond is the most polar?
"Which C–X bond is the most polar?" is a free, interactive Class 12 Chemistry simulation for NEET and JEE, built on the NCERT section "The carbon-halogen bond" in Haloalkanes and Haloarenes. CH₃–X drawn to scale for F, Cl, Br, I: bond length grows, bond enthalpy falls, and the dipole moment (charge × distance) peaks at Cl, not F. NEET has asked about this idea 2 times in 10 years of papers. JEE Main asked 62 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson The carbon-halogen bond in Haloalkanes and Haloarenes. Change the values and watch what happens.
What it shows
NCERT §6.3
CH₃–X drawn to scale for F, Cl, Br, I: bond length grows, bond enthalpy falls, and the dipole moment (charge × distance) peaks at Cl, not F.
Controls
2 to try
- Sliderhalogen F / Cl / Br / I
- Readoutsbond length (pm), bond enthalpy (kJ mol⁻¹), δ charge, dipole moment (D), relative leaving ability
Try this
Find the halomethane with the largest dipole moment and the one whose C–X bond breaks most easily.
Common mistake
CH₃F has the largest dipole moment because F is most electronegative.
In NEET
10 years of papers
Asked 2 times in 10 years of NEET.
See the past questions: Nucleophilic Substitution, Haloalkanes and Haloarenes (chapter)
In JEE Main
42 shifts analysed
62 questions from Haloalkanes and Haloarenes across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT §6.3
- A halogen is more electronegative than carbon, so the C–X bond is polar: carbon carries a partial positive charge (δ+) and the halogen a partial negative charge (δ−).
- Down the group the halogen atom grows (F smallest, I largest), so the C–X bond lengthens from C–F to C–I.
- Bond lengths in the methyl halides: CH₃–F 139 pm, CH₃–Cl 178 pm, CH₃–Br 193 pm, CH₃–I 214 pm.
- C–X bond enthalpies fall as the bond lengthens: 452 (C–F), 351 (C–Cl), 293 (C–Br) and 234 (C–I) kJ mol⁻¹.
- Dipole moments: CH₃F 1.847 D, CH₃Cl 1.860 D, CH₃Br 1.830 D, CH₃I 1.636 D. The largest is for CH₃Cl, not CH₃F: F has the bigger charge separation but the far shorter bond.
- The δ+ carbon is the site a nucleophile attacks, and the weaker, longer C–I bond breaks most easily; this explains the reactivity order R–I > R–Br > R–Cl > R–F met later.
Questions
5 answers
- What does the "Which C–X bond is the most polar?" simulation show?
- CH₃–X drawn to scale for F, Cl, Br, I: bond length grows, bond enthalpy falls, and the dipole moment (charge × distance) peaks at Cl, not F.
- What mistake does the "Which C–X bond is the most polar?" simulation fix?
- A common mistake it clears up: CH₃F has the largest dipole moment because F is most electronegative.
- Has NEET asked about this idea?
- Yes. NEET has asked about this idea 2 times in 10 years of papers.
- Does JEE Main ask questions from Haloalkanes and Haloarenes?
- Yes. JEE Main asked 62 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "The carbon-halogen bond" in Haloalkanes and Haloarenes (Class 12 Chemistry).
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