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MHT-CET : Chemistry Entrance Exam

MHT - CET : Chemistry - Halogen Derivatives of Alkanes Know More


  • Markownikoff's Rule
    When a hydrogen halide is added to an unsymmetrical alkene, the addition across the double bond takes place according to Markownikoff's Rule.
    It states that:
    The negative part (halide part) of the hydrogen halide goes to the carbon atom containing the lowest number of hydrogen atom.
  • Peroxide Effect (Kharsch Effect or Anti-Markownikoff's Effect)
    When an unsymmetrical alkene is treated with HBr in presence of a peroxide (like benzoyl peroxide), Br- ion gets added to the carbon atom (within the double bond) containing the highest number of hydrogen atoms.
    This effect is applicable only for HBr and not for HI, HCl, etc.
    This is because:
    (i) HBr bond is weaker than HCl bond. Hence, HCl bond cannot be broken by the peroxide.
    (ii) HI bond is weaker than HBr bond. The iodine atoms combine to form iodine molecules and hence cannot attack the double bond present in alkenes.
  • The Reaction of Thionyl Chloride (SOCl2) on Alcohol to form Alkyl Chloride is also known as Darzen's Method:
    - OH + SOCl2 R - Cl + HCl + SO2
  • Physical Properties of Alkyl Halides

                                 i.            They are insoluble in water but soluble in organic solvents. This is because they cannot form hydrogen bonds with water.

                               ii.            They are polar in nature.

                              iii.            Their boiling point decreases from fluorine to iodine.

                             iv.            They can show optical and chain isomerism.

  • Grignard Reagent
    It was found by Victor Grignard. It is an organo metallic compound. The C-Mg bond (in R - Mg - X) is a polar covalent bond because C is more electronegative than Mg atom.
  • Inductive Effect (I)
    It is of two types:
    i) +I effect: It is due to the electron repelling or donating groups of atoms.
    ii) -I effect: It is due to the electron accepting or attracting groups of atoms.
  • Electromeric Effect (E)
    It is of two types:
    i) + E effect: This effect occurs when the transfer of electrons takes place towards the attacking reagents.
    ii) - E effect: This effect occurs when the transfer of electrons takes place away from the attacking reagents.

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