Question

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

Short answer

The correct answer is (c) propadiene.

Step-by-step solution

Identify the Reaction Type

The reaction involves the removal of hydrochloric acid (HCl) from allyl chloride (C3H5Cl), which indicates that a dehydrochlorination reaction is taking place.

Understand the Mechanism

Dehydrochlorination of allyl chloride typically involves the elimination of HCl to form a compound with a double bond. This type of elimination leads to the formation of a conjugated or cumulated diene.

Determine the Reaction Product

When HCl is removed from allyl chloride, the most likely result is the formation of a cumulated diene. This compound is known as propadiene (C3H4). The double bond shifts to form CH_2=C=CH_2.

Confirm the Answer

Given the understanding of dehydrochlorination and the structure of allyl chloride, the product is likely to be propadiene. Therefore, the correct answer is (c) propadiene.

Key concepts

Dehydrochlorination

Dehydrochlorination is an important chemical reaction in organic chemistry that involves the removal of a hydrogen chloride molecule, typically resulting in the formation of a carbon-carbon double bond. It is a type of elimination reaction. In this process, a molecule of hydrochloric acid (HCl) is removed from an organic compound. This leads to the formation of an alkene or a form of diene, depending on the structure of the original compound.

In the case of allyl chloride (C3H5Cl), dehydrochlorination involves the loss of an HCl molecule. The hydrogen is abstracted from an adjacent carbon when chlorine is removed, causing electrons to shift and create a double bond.

Key steps involved in dehydrochlorination:

• Identify the presence of HCl in the molecule.
• Determine the location where HCl will be removed.
• Understand that this removal results in the formation of a double bond.

Dehydrochlorination is fundamental for converting compounds into more reactive forms and is widely used in synthetic organic chemistry.

Allyl Chloride

Allyl chloride, scientifically known as 3-chloropropene, is a derivative of propene with the chemical formula C3H5Cl. It possesses a chloro (Cl) functional group attached to a three-carbon alkene chain, specifically at the terminal end.

Allyl chloride's structure features both single and double bonds, making it versatile for various chemical reactions. The double bond in its structure allows for potential transformations such as dehydrochlorination. This ability to react is particularly valuable in producing more complex organic compounds.

Some properties and features of allyl chloride include:

• It is a colorless liquid with a pungent odor.
• It participates mainly in elimination and substitution reactions.
• Its double bond is conducive to forming conjugated systems when reacting under suitable conditions.

Understanding allyl chloride's properties helps in predicting its behavior in chemical reactions such as dehydrochlorination and its eventual transformation into compounds like propadiene.

Propadiene Formation

Propadiene, also known as allene, is a simple linear hydrocarbon with the formula C3H4. It is categorized as a cumulated diene due to the presence of consecutive double bonds in its structure, specifically CH2=C=CH2.

The formation of propadiene from allyl chloride through dehydrochlorination involves an interesting rearrangement of electrons. When HCl is removed from allyl chloride, the electrons shift in such a way that two adjacent carbon atoms gain a pair of double bonds, creating the unique structure of propadiene.

Characteristics of propadiene include:

• It consists of two carbon-carbon double bonds in succession.
• It has significant reactivity due to its pliable electronic structure.
• It can participate in additional chemical reactions, serving as an intermediate in organic synthesis.

The conversion of allyl chloride to propadiene exemplifies the transformation of a chlorinated alkene into a more reactive diene, showcasing the intricate nature of organic transformation reactions.