Haloalkanes and Haloarenes Class 12 Notes - Chapter 10

Based on the structure i.e depending upon the number of halogen atoms in a compound, Alkyl/ Aryl halides are classified as mono, di, and polyhalogen. When compared to carbon, halogen atoms are more electronegative. Therefore

  • The bond (carbon-halogen bond) of alkyl halide is polarised.
  • Halogen atom carries a partial negative charge
  • Carbon atom carries a partial positive

Preparation Of Alkyl Halides

Alkyl halides are produced by the free radical halogenation of alkanes-

  • Step 1 – Adding halogen acids to alkenes
  • Step 2 – Replacing –OH group of alcohols by halogens with the use of phosphorus halides or halogen acids or thionyl chloride

Aryl halides are prepared with the help of electrophilic substitution to arenes. Iodides and Fluorides are prepared with halogen exchange method. Organohalogens have a higher boiling point when compared hydrocarbons due to strong van der Waals forces and dipole-dipole forces. They partial dissolve in water but completely dissolve in organic solvents.

Organometallic compounds are formed by the nucleophilic substitution, elimination, and reaction with metal atoms which occurs due to the polarity of a carbon-halogen bond of alkyl halides. Based on the kinetic properties Nucleophilic substitution reactions are classified as SN1 and SN2. Chirality plays a very important in SN2 reactions of understanding the reaction mechanisms of these reactions. SN2 reactions are characterized by inversion configuration whereas SN1 reactions are characterised by racemisation.

Few Important Questions

  1. Write the IUPAC names of ClCH2C≡CCH2Br
  2. Who has the highest dipole moment from the following?

CCl4 and CH2Cl2

  1. Write the steps to convert Propene to propan-1-ol and Benzyl alcohol to 2-phenylethanoic acid.
  2. Define ambident nucleophiles? Give an example and explain.
  3. When n-butyl chloride is treated with alcoholic KOH, what is the result?

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Practise This Question

 Read the assertion and reason carefully to mark the correct option out of the options given below:

(a)If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b)If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c)If assertion is true but reason is false.

(d)If assertion is false but reason is true.
 Assertion : EV(M2+/M) value for copper is positive (+0.34V).
 Reason :  High ionization enthalpy and low heat of hydration energy