Question

In an alkane halogenation reaction. which of the following steps will never produce a radical? A. initiation B. propagation C. conjugation D. termination

Short answer

C. conjugation

Step-by-step solution

Understand Halogenation

In an alkane halogenation reaction, a halogen is added to an alkane, typically through a series of radical reactions.

Define Each Step in Radical Mechanism

Identify each step involved in a halogenation reaction: Initiation, Propagation, and Termination.

Initiation Step

In the initiation step, radicals are generated. For example, the halogen molecule splits into two halogen radicals.

Propagation Step

During propagation, radicals react with stable molecules to produce new radicals. This generates a chain reaction.

Termination Step

In the termination step, radicals combine to form stable molecules, thereby ending the reaction.

Conjugation Detailed Analysis

Conjugation is not a step in the radical chain mechanism of halogenation of alkanes. It usually refers to the overlapping of p-orbitals in pi-systems.

Determine the Correct Answer

Since conjugation does not produce radicals and is unrelated to the reactions in halogenation, the step that will never produce a radical is conjugation.

Key concepts

Radical Mechanism

In organic chemistry, a radical mechanism involves the formation, reaction, and disappearance of free radicals. Free radicals are atoms or molecules with an unpaired electron, making them highly reactive.

• Formation of Radicals: Radicals are often formed by the breaking of covalent bonds through processes like heat or light.
• Chain Reaction: Once formed, these radicals can perpetuate a chain reaction where more radicals are continuously generated.
• Reactivity: Due to their unpaired electron, radicals can react quickly with other molecules to achieve a more stable state.

Understanding the radical mechanism is key to mastering many organic reactions, including alkane halogenation.

Initiation Step

The initiation step is the beginning phase of a radical chain reaction. During this stage, radicals are produced from stable molecules.

• Example: In alkane halogenation, the halogen molecule (\text{X\(_2\)}) is split into two radicals (\text{X·}) using energy from heat or light. \text{X\(_2\)} \rightarrow \text{2X·}
• Role: These radicals are necessary to start the chain reaction that occurs in subsequent steps.
• Trigger: The initiation step usually requires an external energy source like UV light to break the bonds.

Without the initiation step, the radical chain reaction would never start.

Propagation Step

The propagation step is where the actual