Chemistry – Organic chemistry - Alkanes | e-Consult

The reaction of alkanes with chlorine is a photochemical reaction. This means that light is required to initiate the reaction. Specifically, ultraviolet (UV) light provides the activation energy (E_a) needed to break the Cl-Cl bond, forming chlorine radicals. These chlorine radicals are highly reactive and abstract hydrogen atoms from the alkane molecule, creating alkyl radicals. The alkyl radicals then react with another chlorine molecule to form a chloroalkane product and regenerate a chlorine radical, continuing the chain reaction. This results in a mixture of products, as the chlorine can substitute at different carbon atoms within the alkane chain. The products are primarily monosubstituted chloromethane, but also include dichloromethanes, trichloromethanes, and tetrachloromethane, along with hydrogen chloride (HCl) as a byproduct.

The main organic products formed from the substitution of methane are:

• Chloromethane (CH₃Cl): A methyl group is replaced by a chlorine atom.
• Dichloromethane (CH₂Cl₂): Two hydrogen atoms are replaced by chlorine atoms.
• Trichloromethane (CHCl₃): Three hydrogen atoms are replaced by chlorine atoms.
• Tetrachloromethane (CCl₄): All four hydrogen atoms are replaced by chlorine atoms.

Here are the structural formulae:

• Chloromethane (CH₃Cl): CH₃-Cl
• Dichloromethane (CH₂Cl₂): CH₂Cl-CH₂Cl
• Trichloromethane (CHCl₃): CHCl₃
• Tetrachloromethane (CCl₄): CCl₄