Problem 175 - A Complete Resource Book in Chemistry for JEE Main

Question

Alkyl halides react with dialkyl copper reagents to give \(\mid 2005]\) (a) alkenes (b) alkyl copper halides (c) alkanes (d) alkenyl halides

Step-by-Step Solution

Answer

The reaction produces (c) alkanes.

Step 1: Understanding Alkyl Halides

Alkyl halides, also known as haloalkanes, are compounds in which a halogen atom is bonded to an alkyl group. They are represented as R-X, where R is an alkyl group and X is a halogen.

Step 2: Recognizing Dialkyl Copper Reagents

Dialkyl copper reagents, denoted as R2CuLi, are organocopper compounds used in organic synthesis. The copper is bonded to two alkyl or aryl groups and usually involved in coupling reactions with alkyl halides.

Step 3: Analyzing the Reaction Type

The reaction between alkyl halides and dialkyl copper reagents typically results in a coupling reaction, where the copper reagent transfers an alkyl group to the alkyl halide.

Step 4: Identifying the Product

In this reaction, an alkyl group from the dialkyl copper reagent replaces the halogen on the alkyl halide, producing an alkane. This is known as the core reaction of Gilman reagents.

Step 5: Conclusion

The product of the reaction between an alkyl halide and a dialkyl copper reagent is an alkane, as the alkyl group from the copper reagent attaches to the alkyl chain previously bearing the halogen.

Key Concepts

Understanding Alkyl Halides

Alkyl halides, which are sometimes referred to as haloalkanes, are organic compounds where one or more halogens are bonded to an alkyl group. This is the basic structure: R-X, with 'R' representing the alkyl group and 'X' being a halogen like chlorine, bromine, or iodine. Alkyl halides are versatile in chemical reactions due to their reactive nature, making them key players in various organic synthesis processes. Their reactivity is often attributed to the difference in electronegativity between the carbon atoms in the alkyl group and the halogen atom.

• These halides act as useful intermediates in nucleophilic substitution reactions.
• They are also reactive toward elimination reactions, which lead to the formation of alkenes and other structures.

Understanding the properties and reactions of alkyl halides helps in predicting the structure of the products formed after reactions such as coupling with organocopper compounds.

Exploring Organocopper Compounds

Organocopper compounds, particularly the ones used in organic synthesis, often refer to copper-bearing substances like Gilman reagents. These are typically formed using copper and alkyl or aryl groups. A commonly used form is R₂CuLi, known as a dialkyl copper reagent. These compounds serve as a significant class in organometallic chemistry:

• They have a distinctive characteristic of being nucleophilic.
• They easily participate in reactions where they transfer an alkyl or aryl group from the copper to another molecule.

When these reagents are used with alkyl halides, the result is often a structural transformation that excises the halogen atom and supplants it with an alkyl group from the organocopper compound. The role of copper in such reactions is quite unique as it serves to mediate the transfer of organic groups, resulting in new carbon-carbon bonds, making them incredibly useful for intricate synthesis pathways.

Insight into Coupling Reactions

Coupling reactions involve the joining of two fragments, typically organic moieties, with the aid of a catalyst. In our context, coupling reactions occur when an alkyl halide interacts with a dialkyl copper reagent, leading to the creation of alkanes. The mechanism involves a direct transfer of an organic group from the organocopper compound to the alkyl halide. This reaction replaces the halogen atom in the alkyl halide with an alkyl group, effectively forming a new C-C bond. Coupling reactions are pivotal in building complex molecules as they allow:

• The formation of carbon-carbon bonds.
• The assembly of molecular skeletons with intricate structures.

Because these reactions are so efficient in generating diverse organic compound structures, they are vital in the synthesis of complex organic chemicals and pharmaceuticals. Understanding how coupling reactions work helps in appreciating their broad utility and expansive application in modern organic chemistry.