Question

When chlorine is passed through propene at \(400^{\circ} \mathrm{C}\), which of the following is formed? (a) allyl chloride (b) PVC (c) vinyl chloride (d) 1,2 -dichloroethane

Short answer

At 400°C, free radical chlorination leads to chlorine addition, but no choice matches exactly; closest analog is 1,2-dichloroethane, option (d).

Step-by-step solution

Identify the Reaction Type

When chlorine is passed through an alkene such as propene at high temperatures, a free radical chlorination reaction typically occurs. This happens due to the breaking of double bonds and addition of chlorine atoms.

Analyze the Structure of Propene

Propene, also known as propylene, has the chemical structure of ext{CH}_3 ext{CH}= ext{CH}_2. The double bond between the second and third carbon atoms allows for the addition of chlorine in a free radical reaction.

Determine Product Formation

At high temperatures like 400°C, chlorine breaks into free radicals and can add across the double bond in propene. This results in the addition of chlorine atoms to both carbon atoms originally involved in the double bond.

Identify the Final Product

The addition of chlorine to the double bond in propene results in the formation of 1,2-dichloropropane, which is not listed among the given options. However, considering the choices, 1,2-dichloroethane is the only compound formed through a similar mechanism in tetragonal chlorine additions to an ethylene structure. Due to the close analogs, the intended answer seems to point to a typical addition product similar to choice (d).

Key concepts

Free Radical Reaction

In a free radical reaction, molecules with unpaired electrons, known as radicals, engage in chemical reactions. These radicals are highly reactive and seek to pair their unpaired electrons, which can drive the reaction forward. A common example of a free radical reaction is the chlorination of alkenes. Chlorine molecules (Cl₂) can be split into radicals by exposure to high temperatures or ultraviolet light.
When chlorine is introduced to an alkene such as propene at elevated temperatures, it dissociates into two chlorine radicals. These radicals are then able to add to the carbon atoms of the double bond, forming new chemical bonds. This process is highly significant because it allows the transformation of alkenes into chlorinated products within synthetic chemistry. Using the radical nature of chlorine, various addition products can be synthesized, leading to applications such as the production of PVC and other chlorinated materials.

Propene Structure

Propene, or propylene, is a key organic compound in the realm of alkenes. Its molecular structure can be represented as \, \( \text{CH}_3\text{CH}=\text{CH}_2 \), indicating it has three carbon atoms and a double bond between the second and third carbon.
Understanding propene's molecular structure is essential, especially its double bond. The double bond is a site of high electron density, making it an ideal target for addition reactions. Free radicals can effectively react at this site, altering the structure and forming new products.

• The methyl group \( (\text{CH}_3) \) is connected to the first carbon.
• The double bond exists between the second \( (\text{CH}) \) and third \( (\text{CH}_2) \) carbon atoms.

Due to this structure, propene is a prime candidate for reactions like chlorination, where the double bond provides an avenue for new chemical bonds to form.

Addition Reaction Mechanism

Addition reactions are fundamental chemical reactions in which elements are added to another molecule. In the context of alkenes, such as propene, these reactions frequently occur at the site of the double bond. A typical scenario is when chlorine radicals "add" themselves across a double bond in an alkene.
During the chlorination of propene, chlorine radicals attack the carbon atoms that constitute the double bond. The high reactivity of free radicals facilitates this process. This mechanism involves breaking the double bond and forming two new single bonds with chlorine atoms.
At elevated temperatures, these addition reactions are more favorable since they provide the energy needed to overcome the activation barrier and initiate the reaction. The final result is a saturated compound, like 1,2-dichloropropane, with no double bonds remaining. It's important in different synthetic processes, providing pathways to useful and varied end products.