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Chemistry

Chemistry. Alkyl and Aryl halides–1. Session objectives. Classification Nature of C — X bond Preparation of alkyl halides Physical and chemical properties of alkyl halides Substitution reaction: S N 1 and S N 2 reactions. Elimination reaction. E 1 E 2 E1 c B Ei. E1. Mechanism.

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Chemistry

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  1. Chemistry

  2. Alkyl and Aryl halides–1

  3. Session objectives • Classification • Nature of C — X bond • Preparation of alkyl halides • Physical and chemical properties of alkyl halides • Substitution reaction: SN1 and SN2 reactions

  4. Elimination reaction • E1 • E2 • E1 c B • Ei

  5. E1 Mechanism

  6. Elimination reaction 3° > 2° > 1° > CH3 Rate = k[RX]1

  7. E2 Rate = k[RX] [Base] = k[CH3CH2Cl]

  8. E1 cB carbanion stabilization by the participation of –R (conjugation), –I effect etc. Mechanism

  9. Ei Observed for pyrolytic elimination for xanthates (Tschugaev’s reaction), esters, oxides of amines (Cope’s reaction) which produces alkene. It occurs intramolecularly through the formation of a transition state, when they are heated.

  10. Comparison between E1 and E2

  11. Comparison between E1 and E2

  12. Polyhalogen compounds Dichloromethane (CH2Cl2) Colourless sweet smelling volatile liquid. It has low boiling point (313 k) and inflammable; used as a solvent in extraction in food and pharmaceutical industries. Vicinal dihalide When two halogen atoms are attached to adjacent carbon atoms, the compound is called vicinal dihalide. e.g., 1, 2-dichloroethane

  13. Polyhalogen compounds Geminal dihalide When two halogen atoms are attached to the same carbon atom, the compound is called geminal dihalide e.g. H3C – CHCl2 1,1-dichloroethane

  14. Polyhalogen compounds Chloroform (CHCl3) Methods of preparation (1) By chlorination of methane (2) By reduction of carbon tetra chloride

  15. Polyhalogen compounds (3) From ethyl alcohol

  16. Polyhalogen compounds (4) From acetone

  17. Properties (1)Sweet smelling liquid, boiling point 61° C. (2) Oxidation • Stored in dark coloured bottled because on oxidation chloroform gives phosgene gas which is poisonous • 1% C2H5OH is added while storing chloroform

  18. Properties (3) Reduction (4) Chlorination (5) Hydrolysis (6) Nitration

  19. Properties (7) Reaction with acetone (8) Dehalogenation (9) Carbylamine reaction

  20. Iodoform (CHI3) Preparation

  21. properties • Yellow solid melting point 119° C. • Chemical properties of iodoform are same as that of chloroform. • Chlorine and bromine can replace iodine in iodoform reaction to give CHCl3 and CHBr3 respectively. The reaction is called haloform reaction.

  22. Carbon tetrachloride Preparation Properties (1) Colourless liquid, boiling point 350 K.

  23. Uses (1) Used as fire extinguisher. Trade name is pyrene. At 773 K it is hydrolysed by water vapours into phosgene gas. Therefore, the room should be well ventilated after using CCl4 as fire extinguisher. (2) Industrial solvent for oils, fats, resins etc.

  24. Thank you

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