Halogen derivates of alkanes HDA

12th chemistry chapter halogen derivates of alkanes. Organic synthesis and its uses. Phenomenon like resonance and o,p directing. Classifications

1. Halogen derivatives PRESENTED BY: FREYA CARDOZO Presented by: Freya Cardozo 1

2. Classification based on Hydrocarbon skeleton On the basis of hydrocarbon skeleton to which halogen atom is bonded, the halogen derivatives are classified as haloalkanes, haloalkenes, haloalkynes and haloarenes. Presented by: Freya Cardozo 2

3. Based on no. Of halogen atoms On the basis of number of halogen atoms, halogen derivatives are classified as mono, di, tri or poly halogen compounds. Presented by: Freya Cardozo 3

4. Monohalogen compunds Alkyl halides or haloalkanes Allylic halides Benzylic halides vinylic halides Haloalkynes Aryl halides or haloarenes Presented by: Freya Cardozo 4

5. Haloalkanes or alkyl halides halogen atom is bonded to sp 3 hybridized carbon which is a part of saturated carbon skeleton. Alkyl halides may be primary, secondary or tertiary depending on the substitution state of the carbon to which halogen is attached Presented by: Freya Cardozo 5

6. Identify Presented by: Freya Cardozo 6

7. Allylic halides In allylic halides, halogen atom is bonded to a sp 3 hybridized carbon atom next to a carbon-carbon double bond Presented by: Freya Cardozo 7

8. Benzylic halides In benzylic halides halogen atom is bonded to a sp 3 hybridized carbon atom which is further bonded to an aromatic ring . Presented by: Freya Cardozo 8

9. Vinylic halides In vinylic halides halogen atom is bonded to a sp 2 hybridized carbon atom of aliphatic chain. Vinylic halide is a haloalkene. Presented by: Freya Cardozo 9

10. Haloalkynes When a halogen atom is bonded to a sp hybridized carbon atom it is a haloalkyne. Presented by: Freya Cardozo 10

11. Haloarenes or aryl halides In aryl halides, halogen atom is directly bonded to the sp 2 hybridized carbon atom of aromatic Ring . Presented by: Freya Cardozo 11

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14. Things you need to know! Carbon ke 4 haath hai , so it can always form only 4 bonds - ane = single bonds, ene = double bond, yne = triple bond, - ol = OH group i.e. alcohol Rememeber 1 C Methane F Fluoride Fluoro 2 C Ethane Br Bromine Bromo 3 C Propane Cl Chlorine Chloro 4 C Butane I Iodine Iodo 5 C Pentane 6 C Hexane Presented by: Freya Cardozo 14

15. Preperation of alkyl halide Presented by: Freya Cardozo 15

16. Four main methods Presented by: Freya Cardozo 16

17. From Alcohols- Hydrogen acids R-OH + HX Presented by: Freya Cardozo 17

18. From HCl Presented by: Freya Cardozo 18

19. Using HBr Presented by: Freya Cardozo 19

20. Using HI Presented by: Freya Cardozo 20

21. Phosphorus trichloride PCl 3 Presented by: Freya Cardozo 21

22. Phosphorus pentachloride PCl 5 Presented by: Freya Cardozo 22

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24. Thionyl Chloride SOCl 2 Presented by: Freya Cardozo 24

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26. From Hydrocarbons Alkanes Alkenes Alkenes + CCl 4 Presented by: Freya Cardozo 26

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29. Write reaction and iupac name of major product Presented by: Freya Cardozo 29

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31. Halogen exchange reaction Finkelstein reaction Presented by: Freya Cardozo 31

32. Swartz reaction Presented by: Freya Cardozo 32

33. Electrophilic substitution Presented by: Freya Cardozo 33

34. Electrophilic substitution Presented by: Freya Cardozo 34

35. Questions Convert But-1-ene to n-butyl iodide Aniline to chlorobenzene Presented by: Freya Cardozo 35

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39. Physical properties Presented by: Freya Cardozo 39

40. Bond strength Carbon atom that carries halogen develops a partial positive charge while the halogen carries a partial negative charge. Thus carbon-halogen bond in alkyl halide is a polar covalent bond. Therefore alkyl halides are moderately polar compounds Size of the halogen atom increases from fluorine to iodine. Hence the C-X bond length increases. The C-X bond strength decreases with an increase in size of halogen. This is because as the size of p-orbital of halogen increases the p-orbital becomes more diffusedand the extent of overlap with orbital of carbon decreases Presented by: Freya Cardozo 40

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42. Boiling point Boiling points of alkyl halides are considerably higher than those of corresponding alkanes due to higher polarity and higher molecular mass For alkyl halides with same R group the B.P depends upon the size of halogen atom.More larger the atom more is B.P . Because Vander waals forces increase Thus boiling point of alkyl halide decreases in the order RI > RBr > RCl > RF Presented by: Freya Cardozo 42

43. 2. With same X atom and different R group... Longer R group chain or more number of carbon atoms More is the Vander waal forces Higher B.p Presented by: Freya Cardozo 43

44. 3. For isomeric alkanes i.e R group with same number of carbon atoms More the branching Lesser the surface area Lesser Vander waal forces Thus lesser B.P Presented by: Freya Cardozo 44

45. Question Arrange the following compounds in order of increasing boiling points : bromoform, chloromethane, dibromomethane, bromomethane. Presented by: Freya Cardozo 45

46. Solubility Though alkyl halides are moderately polar, they are insoluble in water. It is due to inability of alkyl halides to form hydrogen bonds with water. Attraction between alkyl halide molecules is stronger than attraction between alkyl halide and water. Alkyl halides are soluble in non-polar organic solvents. Aryl halides are also insoluble in water but soluble in organic solvents. Presented by: Freya Cardozo 46

47. Alkyl halides though polar are immiscible with water.Give reason Presented by: Freya Cardozo 47

48. Reactions of alkyl halides Lab test Substitution reactions Dehydrohalogrnation/ beta elimination Presented by: Freya Cardozo 48

49. Lab test Presented by: Freya Cardozo 49

50. Substitution reactions Formation of alcohol Amines cyanide Isocyanide Esters
Ethers Nitroalkanes Alkyl nitrite Presented by: Freya Cardozo 50

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59. Optical activity Presented by: Freya Cardozo 59

60. Draw 2-chlorobutane Presented by: Freya Cardozo 60

61. Carbon atom in a molecule which carries four different groups/atoms is called chiral carbon atom. Thus, the C-2 in 2-chlorobutane is a chiral carbon. Chiral atom in a molecule is marked with asterisk (*). Presented by: Freya Cardozo 61

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64. Optical isomers and optical activity The stereoisomerism in which the isomers have different spatial arrangements of groups/atoms around a chiral atom is called optical isomerism. The optical isomers differ from each other in terms of a measurable property called optical activity Presented by: Freya Cardozo 64

65. Plane polarized light light having oscillations only in one plane perpendicular to direction of propagation of light is known as plane polarized light. Presented by: Freya Cardozo 65

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67. Definitions property of a substance by which it rotates plane of polarization of incident plane polarized light is known as optical activity. The compounds which rotate the plane of plane polarized light are called optically active compounds and those which do not rotate it are optically inactive compounds. Optical activity of a substance is expressed numerically in terms of optical rotation. The angle through which a substance rotates the plane of plane polarized light on passing through it is called optical rotation. In accordance with the direction of optical rotation an optically active substance is either dextrorotatory or laevorotatory. A compound which rotates the plane of plane polarized light towards right is called dextrorotatoryand designated by symbol d- or by (+)sign. A compound which rotates plane of Plane polarized light towards left is called laevorotatory and designated by symbol l-or by (-) sign. Presented by: Freya Cardozo 67

68. Enantiomers The optical isomers which are non-superimposable mirror image of each other are called enantiomers or enantiomorphs or optical antipodes. Enantiomers have equal and opposite optical rotation. Thus, enantiomers are a kind of optical isomers. Enantiomers have identical physical properties (Such as melting point, boiling points, densities, refractive index) except the sign of optical rotation. The magnitude of their optical rotation is equal but the sign of optical rotation is opposite. They have identical chemical properties except towards optically active reagent. Presented by: Freya Cardozo 68

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70. Racemic mixture An equimolar mixture of enantiomers (dextrorotatory and laevorotatory) is called racemic modification or racemic mixture. A racemic modification is optically inactive because optical rotation due to molecules of one enatiomer is cancelled by equal and opposite optical rotation due to molecules of the other enantiomer. A racemic modification is designated as (dl) or by (±) sign. Presented by: Freya Cardozo 70

71. SN mechanism Presented by: Freya Cardozo 71

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75. Distinguish between Presented by: Freya Cardozo 75

76. Factors influencing SN1 and SN2 mechanism Nature of substrate Nucleophilicity of reagent solvent polarity Presented by: Freya Cardozo 76

77. Nature of substrate 1° alkyl halide – SN2 reaction 3° alkyl halide – SN1 reaction T.S in SN2 is pentacoordinate carbon which is crowded this not favoured by 3° Steric hinderance doesn’t allow 3° to proceed by this mechanism For SN1 it proceeds with formation of carbocation which is stabilized by hyperconjugation and +I inductive effect of alkyl group Thus favours 3° R-X Presented by: Freya Cardozo 77

78. Nucleophilicity of reagent Nucleophilicity is similiar to concept of Lewis base Lewis base- donates an electron pair easier the nucleophile donating the electron pair better Nucleophilic reagent In SN2 reaction rate depends on nucleophile thus stronger nucleophile will be needed for such reaction Poor nucleophile undergo SN1 beacuse rate is independent of nucleophile Presented by: Freya Cardozo 78

79. Solvent polarity SN1 reactions proceed rapidly in protic and polar solvents SN1mechanism proceeds via formation of carbocation intermediate. A good ionizing solvent, polar solvent, stabilizes the ions by solvation. Cations are poorly solvated but anions solvation is of key importance Anions are solvated by hydrogen bonding solvents, that is, protic solvents Presented by: Freya Cardozo 79

80. aprotic solvents or solvents of low polarity will favour SN2 mechanism. Polar protic solvents usually decrease the rate of SN2 reaction. In the rate determining step of SN2 mechanism substrate as well as nucleophile is involved. A polar solvent stabilizes nucleophile (one of the reactant) by solvation. Thus solvent deactivates the nucleophile by stabilizing it. Presented by: Freya Cardozo 80

81. Which of the following two compounds would react faster by SN2 mechanism and Why ? 1-chlorobutane and 2-chlorobutane Presented by: Freya Cardozo 81

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85. Primary allylic and primary benzylic halides show higher reactivity by SN1 mechanism than other primary alkyl halides. Explain. Presented by: Freya Cardozo 85

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89. Haloarenes Presented by: Freya Cardozo 89

90. Sandmeyers reaction Aniline reacts with nitrous acid HNO2 (NaNo2 + HCl) to give benzene diazonium chloride which when treated with copper chloride forms Chlorobenzene and nitrogen gas. Presented by: Freya Cardozo 90

91. Reaction with metals Presented by: Freya Cardozo 91

92. Fittig Reaction Presented by: Freya Cardozo 92

93. Wurtz fittig Reaction Presented by: Freya Cardozo 93

94. G.R Why cleavage of C-X bonds in haloarenes proceeds with great difficulty? Resonance effect Sp2 hybridization of carbon chlorine Presented by: Freya Cardozo 94

95. How to break C-X bond Placing –I or electronwithdrawing groups at the o or p position More grps easier reaction Presented by: Freya Cardozo 95

96. Nucleophilic substitution Presented by: Freya Cardozo 96

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98. GR. Therefore Cl is o-/p- directing but ring deactivating group. Presented by: Freya Cardozo 98

99. GR. Aryl halides undergo electrophilic substitution reaction slowly as compared to benzene. In resonance structures of chlorobenzene elelctron density is relatively more at ortho and para position. Therefore incoming electrophilic group is more likely to attack at these positions. But due to steric hinderance at ortho position, para product usually predominates. In haloarenes, halogen atom has strong electron withdrawing inductive effect (-I). This deactivates the ring and electrophilic substitution reaction occurs slowly. Presented by: Freya Cardozo 99

100. Electrophilic substitution Presented by: Freya Cardozo 100

101. Halogenation Presented by: Freya Cardozo 101

102. Nitration Presented by: Freya Cardozo 102

103. SULphonation Presented by: Freya Cardozo 103

104. Fridel crafts Alkylation Presented by: Freya Cardozo 104

105. Fridel crafts acylation Presented by: Freya Cardozo 105