MCQ Detailed View

Alkyl halides, also called haloalkanes, are organic compounds in which a halogen atom (Cl, Br, I, or F) is bonded to a saturated carbon atom. These compounds are reactive because the carbon–halogen bond is polarized. Carbon carries a partial positive charge (δ⁺) while halogen carries a partial negative charge (δ⁻). This polarization makes alkyl halides highly susceptible to certain types of reactions.

The two most common reactions of alkyl halides are nucleophilic substitution and elimination.

1. 
   

   Nucleophilic substitution (SN1 and SN2):
   In this reaction, the halogen atom is replaced by a nucleophile. Since halogens are good leaving groups, they depart as halide ions (Cl⁻, Br⁻, I⁻). There are two main mechanisms:

   
   
   
   
   • 
     

     SN1 (unimolecular substitution): Proceeds in two steps, with carbocation formation as the intermediate. It is favored in tertiary alkyl halides.

     
     
   
   
   • 
     

     SN2 (bimolecular substitution): A one-step mechanism where the nucleophile attacks the carbon simultaneously as the halogen leaves. It is common in primary alkyl halides.

     
     
   
   
   
   


2. 
   

   Elimination (E1 and E2):
   In elimination, a hydrogen atom and a halogen atom are removed from adjacent carbon atoms, leading to the formation of an alkene.

   
   
   
   
   • 
     

     E1 (unimolecular elimination): Proceeds via carbocation intermediate, similar to SN1.

     
     
   
   
   • 
     

     E2 (bimolecular elimination): A one-step mechanism where base abstracts a proton while halogen leaves.

     
     
   
   
   
   

Nucleophilic addition does not occur in alkyl halides because it is a characteristic reaction of compounds with multiple bonds such as carbonyl groups.

Therefore, alkyl halides usually undergo nucleophilic substitution and elimination reactions, making the correct choice Both A & C.