AP Inter 2nd Year Chemistry Notes Chapter 11 Haloalkanes and Haloarenes

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AP Inter 2nd Year Chemistry Notes 11th Lesson Haloalkanes and Haloarenes

→ Haloalkanes (or) Haloarenes are formed by-the replacement of hydrogen atom (s) in a hydrocarbon by halogen atom (s).

→ Haloalkanes contain halogen (s) attached to sp3 – hybridised carbon where as in haloarenes halogen (s) attached to sp2 – hybridised carbon.

→ On the basis of number of halogen atoms halo alkanes (or) halo arenes classified as mono halo alkane/arene, Dihaloalkane/arene, Trihaloalkane/arene.

→ Comppunds containing sp3 C – X bond are (a) Alkyl halides (b) Allylic halides (c) Benzylic halides.

→ Compounds containing sp2 C – X bond are (a) Vinylic halides (b) Aryl halides.

AP Inter 2nd Year Chemistry Notes Chapter 11 Haloalkanes and Haloarenes

→ The carbon-halogen bond of alkyl halide is polarised due to high electronegativity of halogen atoms than carbon.
AP Inter 2nd Year Chemistry Notes Chapter 11 Haloalkanes and Haloarenes 1

→ Alcohols undergo treatment with HX/ZnCl2 (or) PX3 (or) PX5 (or) SOCl2 to form alkyl halides.

→ Alkyl halides arylhalides are prepared by

  1. free radical halogenation
  2. Electrophillic substitution
  3. Sandmeyer’s reaction
  4. The addition of hydrogen halide or halogens toalkenes.

→ The boiling points of alkyl halides decrease in the order RI > RBr > RCl > RF.

→ Due to polar nature of C-X bond haloalkanes under go Nucleo phillic substitution reactions 1) SN2-Reactions ii) SN1-reactions.

→ The order of reactivity of alkyl halides in SN2-reactions as follows 1°-alkyl halide > 2°-alkyl halide > 3°-alkyl halide.

→ The order of reactivity of alkyl halides in SN1-reactions as follows 3°-alkyl halides > 2°-alkyl halides > 1°-alkyl halides.

→ SN2-mechanism results in the formation of inversion configurated product where as SN1– mechanism results in the formation of racemised product.

→ Alkyl halides undergo elimination reaction with alc.KOH to form preferred product alkene. This is called dehydro halogenation reaction.

AP Inter 2nd Year Chemistry Notes Chapter 11 Haloalkanes and Haloarenes

→ Alkyl halides react with certain metals to form C-metal bonds containing compounds which are known as organometallic compounds.
Eg.: Grignard reagent (RMgX).

→ Halo arenes undergo nucleophillic substitution, electrophilic substitution reactions.

→ Alkyl halides and aryl halides mixed in presence of Na and dry ether forms alkyl arene. This is called Wurtz-Fitting reaction. If only aryl halides are mixed then the reaction is called Fitting reaction.

→ Poly halogen compounds mostly useful in industry and agriculture. Some examples of poly halogen compounds are CH2Cl2, CHCl3, CHI3, DDT, Freons, CCl4.