Haloalkanes and Haloarenes

Physical and Chemical Properties of Haloalkanes

  • Physical properties of Haloalkanes:
    (a) Insoluble in water, though polar, because of being incapable of forming H-bond.
    (b) Branches decrease boiling points.
  • (c) Boiling point for same halogen increase in R group CH3Cl < CH3CH2Cl < CH3CH2CH2-Cl
    (d) Boiling point increase for same alkyl group as I > Br > Cl > F
                                                 C2H5I > C2H5Br > C2H5Cl > C2H5F
    (e) Density increases with increase in number of halogens and mass of halogen
                        C2H5I > C2H5Br > C2H5Cl > C2H5F ; CH3Cl > CH2Cl2 > CHCl3 > CCl4
    (f) Dipole moment
            CH3Cl (1.860D) > CH3F (1.847 D) > CH3Br (1.830D) > CH3I (1.636 D)
    (g) Stability: RF > RBr > RCl > RI
    (h) Alkyl iodides become dark due to the formation of I2
                 2RI → R − R + I2
  • Some physical properties of haloarenes:
    (a) Insoluble in water due to lack of formation of H-bond.
    (b) Density and b.p. same as in case of haloalkanes.
    (c) Dipole moment:

  • (d) O-Dichloro benzene has less dipole moment than the expected value because the steric effect of two Cl-atoms at -O- positions increases the bond angle than 60°.
    (e) P-Dichloro benzene is used as antimoth compound and room freshener in ODONIL.
    (f) Melting points: P-Dichloro benzene, because of best packing in solid state, among dichloro benzenes, has highest m.p 53°C and meta isomer the lowest 33°C, O-Dichloro benzene melts at 43°C
    (g) Boiling points: O-Dichloro benzene (179°C) > para isomer (172°C) ≈ meta isomer.

View the Topic in this Video from 30:30 to 36:40

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