In organic chemistry, dihalides are compounds that contain two halogen atoms (Cl, Br, I, or F) attached to a hydrocarbon chain. Depending on the position of the halogen atoms, dihalides are classified into two main types:
Vicinal dihalides – when the...
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In organic chemistry, dihalides are compounds that contain two halogen atoms (Cl, Br, I, or F) attached to a hydrocarbon chain. Depending on the position of the halogen atoms, dihalides are classified into two main types:
Vicinal dihalides – when the two halogen atoms are attached to two adjacent carbon atoms.
Example: CH₂Cl–CH₂Cl (1,2-dichloroethane).
The word "vicinal" comes from the Latin vicinus meaning “neighboring.”
Geminal dihalides – when the two halogen atoms are attached to the same carbon atom.
Example: CHCl₂–CH₃ (1,1-dichloroethane).
The word "geminal" comes from gemini meaning “twins.”
Because the definition in the question clearly states two halogen atoms on two adjacent carbons, which is the exact definition of a vicinal dihalide.
Option 1 (Glycols): These are compounds with two hydroxyl (–OH) groups on adjacent carbons, not halogens.
Option 3 (Geminal dihalides): Wrong, because geminal dihalides have both halogen atoms on the same carbon atom.
Option 4 (Diols): These contain two hydroxyl groups (–OH) but no halogens.
They are commonly prepared by the halogenation of alkenes. For example, when ethene reacts with Br₂, vicinal dibromoethane is formed.
They are important intermediates in organic synthesis. For example, vicinal dihalides can undergo dehydrohalogenation to form alkynes.
Industrially, compounds like 1,2-dichloroethane are used in the manufacture of vinyl chloride (PVC production).
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