The most common type of chemical reaction that alkanes undergo is
- A. Substitution
- B. Addition
- C. Condensation
- D. Polymerisation
- E. Double decomposition
Correct Answer: Option A
Explanation
Alkanes are the simplest type of organic compound. They are saturated hydrocarbons with only carbon (C) and hydrogen (H) atoms connected by single bonds. Most of the time, alkanes go through a chemical reaction called substitution, which is part of a group of reactions called radical halogenation.
In substitution reactions, one or more atoms in a molecule are replaced by other atoms or groups of atoms, making a new compound. Radical halogenation is a type of substitution reaction in which a fluorine, chlorine, bromine, or iodine atom swaps places with a hydrogen atom in an alkane. This process happens through a radical mechanism with three steps: starting, spreading, and ending.
- Initiation: The reaction starts when ultraviolet (UV) light or heat breaks a halogen molecule (X2) into two halogen radicals (X•). This gives the bond the energy it needs to break.
- Propagation: The halogen radical reacts with the alkane molecule, taking away a hydrogen atom and making a new bond with the carbon. This makes a hydrocarbon radical (R•) and a hydrogen halide (HX). The hydrocarbon radical then reacts with another halogen molecule to make the desired haloalkane (RX) and bring back the halogen radical.
- Termination: The reaction is over when two radicals join together to make a stable molecule, which stops the chain reaction.
The Bottom Line
Due to how stable alkanes are, radical halogenation is the most common substitution reaction they go through. This is because it allows more reactive functional groups to be added, which makes it easier for more chemical changes to happen.