HALOALKANES & HALOARENES.pppppppppppppppppppppppptx

class 12, cbse, halo alkanes and halo arenes.

1. HALOALKANES & HALOARENES rohii

2. In haloalkanes, the halogen atom(s) is(are) attached to the sp3 hybridized carbon atom(s) of alkyl group whereas in haloarenes, the halogen atom(s) is(are) attached to sp2 hybridized carbon atom(s) of an aryl group. ALKANE/ARENE USES 1] Chlorine containing antibiotic chloromycetin 1] Treatment of Typhoid 2] Iodine containing hormone thyroxine 2] Deficiency of which causes goitre 3] Chloroquine 3] Treatment of Malaria Fever 4] Halothane (CF3-CHClBr) 4] Anaesthetic 5] Agriculture

3. Classification on Basis of Number of Halogen atoms (a) Haloalkanes: T he halogen derivatives of alkanes are called haloalkanes. These are classified as fluoro (F), chloro (Cl), bromo(Br) or iodo (I) compounds according to the type of halogen present and as mono-, di-, tri-, tetra haloalkanes, etc. according as they contain one, two, three, four etc. halogen atoms respectively in their molecules . 1 1 2 1 2 3 Methyl Chloride 1,2-di Chloro Ethane 1,2,3-tri Chloro Propane Eg --- X = Cl

4. Alkyl halides are classified as primary (1°), secondary (2⁰) and tertiary (3°) according as the halogen atom is attached to primary, secondary and tertiary carbon atom respectively. 1 1 2 1 2 3 b) Allylic Halides are compounds in which the halogen atom is connected to the carbon adjacent to the C=C double bond ie to a sp3 hybridized carbon .

5. c) Benzylic Halides these are compounds in which the halogen is attached to a sp3 hybridized carbon ie attached to the aromatic ring. If Carbon is sp3 Hybridized Halo Alkanes Allylic Halides Benzylic Halides

6. Compounds Containing sp2-X Bond If Carbon is sp2 Hybridized Aryl Halides Vinylic Halides a) Aryl Halides : Compounds in which halogen is bonded directly to sp2 hybridised carbon of an aromatic ring a) Vinylic Halides : Compounds in which halogen is bonded to sp2 hybridised carbon

7. IUPAC Naming

8. IUPAC Naming DiHaloAlkanes : having halogen atoms on same carbon are known as geminal di halides(gem). They are named as alkylidene di-halide. Having halogen atoms on adjacent carbon atoms are known as vicinal di halides . They are named as alkylene di-halide .

9. NATURE of C-X BOND Fluorine Chlorine Bromine Iodine Size Bond length Due to electronegativity between C and halogen, the shared pair of electron lie near the halogen. Since the size of atom increases as we move down the group , hence size of fluorine is smallest and iodine is the largest. As a result the Carbon halogen bond length increases and the bond enthalpy decreases. (energy reqd. to break bond) As we move down electronegativity decreases, as a result polarity and dipole moment also decreases Dipole mmt of CH3F should be greater than that of CH3Cl because the size of CH3F is very small, hence the product of charge and distance ie . Dipole moment is slightly lower than CH3Cl . Bond enthalpy Electro-negativity Polarity Dipole moment

10. METHODS OF PREPERATION OF HALOALKANES From Alcohols: 1. The hydroxyl group of an alcohol replaces the halogen on reaction with thionyl chloride(SO2,SOCl2), halogen acids(HCl), phosphorus halides(KI). 2. Thionyl Chloride is preferred because it produces SO2 gas and HCl which evaporate and only pure alkyl halide remains. 3. The reaction with primary and secondary alcohols require the presence of catalyst ZnCl2 . 4. With tertiary alcohols the reaction is conducted by simply shaking the alcohol with conc HCl at room temperature. 5. Constant boiling with HBr gives alkyl bromide. 6. Good yields in R-I may be obtained by heating alcohols with sodium or potassium iodide in 95% orthophosphoric acid. 7. Phosphorus tribromide and triiodide are usually generated in situ(produced in the reaction mixture) by the reaction of red phosphorus with bromine and iodine respectively.

11. From Hydrocarbons: (I) From alkanes by free radical halogenation: Free radical halogenation of chloro or bromo alkanes gives a complex mixture of mono and polyhaloalkanes.

12. (II) From Alkenes (a) Addition of hydrogen halide: An alkene is converted to alkyl halide by reacting it with hydrogen chloride, iodide or bromide. C C + H X c c Propene yields two products however only one predominates as per Markonikovs rule. *textbook H X

13. (b) Addition of Halogens: To for vicinal di-halides.

14. (III) Halogen Exchange Further when the bromo/ chloro compound is reacted with metallic fluoride (SbF3,AgF,CoF2,Hg2F2) it gives a fluoro compound this is known as Swarts reaction.