Alkenes are produced from dehalogenation of ?

The process of dehalogenation involves the removal of halogen atoms from an organic compound. When this process occurs in a vicinal dihalo alkane (a compound in which two halogen atoms are attached to adjacent carbon atoms), the product formed is an alkene.

Reaction Example:
CH₂Br–CH₂Br → CH₂=CH₂ + 2HBr

This transformation takes place under the influence of a reducing agent such as zinc dust in the presence of alcohol (Zn/EtOH). The zinc reacts with halogen atoms to remove them from the molecule, leading to the formation of a carbon–carbon double bond.

Mechanism:

1. 
   

   Zinc donates electrons to halogen atoms, forming ZnX₂ (where X is the halogen).

   
   


2. 
   

   Both halogen atoms are removed from adjacent carbon atoms.

   
   


3. 
   

   The carbon atoms, now electron-deficient, form a π-bond, resulting in an alkene.

   
   

Vicinal dihalo alkanes vs. Geminal dihalo alkanes:

• 
  

  Vicinal dihalo alkane: Halogen atoms on adjacent carbon atoms → form alkene after dehalogenation.

  
  


• 
  

  Geminal dihalo alkane: Both halogens on same carbon atom → may form carbene or other products, not a simple alkene.

  
  

Example Reaction:
1,2-Dibromoethane → Ethene + 2HBr
(CH₂Br–CH₂Br → CH₂=CH₂ + 2HBr)

Key Points:

• 
  

  Type of reaction: Dehalogenation (removal of halogens).

  
  


• 
  

  Reagent used: Zinc in alcohol.

  
  


• 
  

  Product formed: Alkene (due to formation of C=C bond).

  
  


• 
  

  Important condition: Halogens must be on adjacent carbons (vicinal).

  
  

Thus, alkenes are specifically produced from the dehalogenation of vicinal dihalo alkanes.

✅ Correct Option: C) Vicinal dihalo alkane