AP | A-Level | IB | NCERT 11 + 12 – FREE NOTES, RESOURCES AND VIDEOS!
NCERT Class 12
YouTube Channel
YouTube Channel
@chemistry.student
1 Solutions 2 Electrochemistry 3 Chemical Kinetics 4 The d-and f-Block Elements 5 Coordination Compounds 6 Haloalkanes and Haloarenes 7 Alcohols, Phenols and Ethers 8 Aldehydes, Ketones and Carboxylic Acids 9 Amines 10 Biomolecules

6 Haloalkanes and Haloarenes

6.1 Classification of Haloalkanes and Haloarenes 6.2 Nomenclature 6.3 Nature of C–X Bond 6.4 Methods of Preparation of Haloalkanes 6.5 Preparation of Haloarenes 6.6 Physical Properties 6.7 Chemical Reactions 6.8 Polyhalogen Compounds

Nature of C–X Bond

NCERT Reference: Chapter 6 – Haloalkanes and Haloarenes – Page 155

Quick Notes

  • The C–X bond in haloalkanes/haloarenes is polar due to the difference in electronegativity between carbon and halogen.
    • The carbon atom is slightly positive (δ+) and the halogen is slightly negative (δ−).
  • Bond polarity decreases down the halogen group:
    C–F > C–Cl > C–Br > C–I.
  • Bond length increases from C–F to C–I, while bond strength decreases in the same order.
  • Reactivity of halo compounds is significantly influenced by the bond dissociation enthalpy of the C–X bond.

Full Notes:

In haloalkanes and haloarenes, the carbon–halogen bond (C–X) plays a central role in determining the physical and chemical properties of the compound.

Polarity of the C–X Bond

The halogen atoms (F, Cl, Br) are more electronegative than carbon. This creates a polar bond:

NCERT Chemistry Class 12 — schematic showing polar C–X bond with partial charges δ+ on carbon and δ− on halogen for haloalkanes and haloarenes.

Note - the polarity of I is actually similar to carbon and the C–I bond is only weakly polar however the iodine is easily polarisable, meaning the bond readily behaves like a polar bond.

Bond Polarity Trend (Electronegativity-Based)

The degree of polarity depends on the electronegativity difference between C and X:

Bond Strength and Bond Length

As the size of the halogen atom increases the C–X bond length increases and the bond strength (bond dissociation enthalpy) decreases

NCERT Chemistry Class 12 — trend chart of carbon–halogen bonds showing increasing bond length and decreasing bond dissociation enthalpy from C–F to C–I.

Reactivity Implication

The lower the bond dissociation enthalpy, the easier it is to break the bond. Thus, C–I bonds are more reactive in substitution and elimination reactions than C–F bonds.

Summary