Problem 93 - A Complete Resource Book in Chemistry for JEE Main

Question

Allyl chloride on dehydrochlorination gives (a) propylene (b) acetone (c) propadiene (d) allyl alcohol

Step-by-Step Solution

Answer

The product of the reaction is (c) propadiene.

Step 1: Understanding the Reaction

Allyl chloride is an organic compound with the formula CH2=CH-CH2Cl. Dehydrochlorination involves the removal of hydrogen chloride (HCl) from the molecule.

Step 2: Determine the Elimination Process

During dehydrochlorination, a hydrogen atom is removed from a carbon adjacent to the carbon bonded to chlorine. Here, allyl chloride (CH2=CH-CH2Cl) loses HCl to form a double bond.

Step 3: Analyze Possible Products

Removing HCl from allyl chloride leaves a molecule with two double bonds, converting the structure to CH2=C=CH2, which is propadiene.

Step 4: Identify the Correct Product

Examine the possible transformations and structure changes. Upon losing HCl, the product becomes propadiene (option c).

Key Concepts

Understanding Allyl Chloride

Allyl chloride is an important compound in organic chemistry, known for its ability to undergo various reactions. Its chemical structure is represented as \( \text{CH}_{2}=\text{CH}-\text{CH}_{2}\text{Cl} \). This structure contains both a chlorine atom and a carbon-carbon double bond, which makes it a reactive molecule.

• The chlorine atom is bonded to the terminal carbon of the propylene chain.
• The presence of the chlorine makes this molecule susceptible to nucleophilic substitution reactions.

The innate reactive nature of allyl chloride allows it to engage in processes like dehydrochlorination, making it versatile in generating various useful chemical compounds.

Dehydrochlorination Process

Dehydrochlorination is a common method for transforming organic compounds by removing hydrogen chloride (HCl) from a molecule. This process often occurs in the presence of a base, which facilitates the removal of the hydrogen and chlorine atoms.

• In allyl chloride, dehydrochlorination involves breaking the bonds of adjacent hydrogen and chlorine.
• This elimination results in the formation of an additional double bond between carbon atoms.

By removing HCl, the molecular structure undergoes significant alteration, creating new, often more stable compounds like dienes. The dehydrochlorination of allyl chloride transforms it into propadiene, a compound with greater unsaturation.

Formation of Propadiene

Propadiene is an interesting and useful product formed from the dehydrochlorination of allyl chloride. This molecule has the formula \( \text{CH}_{2}=\text{C}=\text{CH}_{2} \), showing its characteristic two double bonds.

• This compound is also known as allene, highlighting its similarity with other unsaturated hydrocarbons.
• Propadiene demonstrates resonance and higher reactivity due to its conjugated double bond system.

The flexibility and reactivity of propadiene make it valuable in chemical syntheses and industrial applications. Its formation from allyl chloride through dehydrochlorination illustrates the powerful transformations possible through elimination reactions.

Elimination Reaction in Organic Chemistry

Elimination reactions are a fundamental aspect of organic chemistry, involving the removal of components from a molecule to form a new product, typically with the introduction of double or triple bonds. This class of reactions is crucial for the creation of unsaturated compounds.

• Elimination reactions often require a base to abstract a proton, facilitating the departure of a leaving group such as a halide.
• These reactions are characterized by the conversion of single bonds to multiple bonds, increasing the molecule's unsaturation.

In the case of the dehydrochlorination of allyl chloride, the elimination reaction transforms it into propadiene, demonstrating the formation of a diene. Understanding how elimination reactions work is integral for predicting and utilizing the structural changes and new bond formations in organic molecules.