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

Question

Alkyl halides react with dialkyl copper reagents to give \([\mathbf{2 0 0 5}]\) (a) alkenes (b) alkyl copper halides (c) alkanes (d) alkenyl halides

Step-by-Step Solution

Answer

(c) alkanes

Step 1: Recognize Reaction Participants

The reaction involves alkyl halides and dialkyl copper reagents. These compounds are commonly used in organocopper coupling reactions.

Step 2: Identify the Reaction Type

The interaction between alkyl halides and dialkyl copper reagents is a type of coupling reaction known as the Gilman reaction.

Step 3: Understand the Reaction Product

In a coupling reaction with dialkyl copper reagents (Gilman reagents), the product is typically an alkane. During the reaction, the alkyl group from the copper reagent replaces the halide in the alkyl halide.

Step 4: Match the Reaction Outcome to Options

Given the typical products of these reactions, match them with the options: (a) alkenes, (b) alkyl copper halides, (c) alkanes, and (d) alkenyl halides. Dialkyl copper reagent reactions typically produce alkanes.

Key Concepts

Alkyl Halides

Alkyl halides, also known as haloalkanes, are a group of chemical compounds derived from alkanes containing one or more halogen atoms (such as fluorine, chlorine, bromine, or iodine) bonded to a carbon atom. These compounds are significant in organic chemistry due to their reactivity, especially in substitution and elimination reactions.

Their general formula is \( ext{R-X}\), where \( ext{R}\) represents an alkyl group, and \( ext{X}\) is the halogen. The nature of the halogen and the type of carbon to which it is attached (primary, secondary, tertiary) greatly influence the chemical behavior of alkyl halides.

Alkyl halides serve as a versatile starting point in organic synthesis, especially in reactions that form new carbon-carbon bonds, such as the Gilman reaction. This reactivity makes them valuable in creating a broad array of chemical products, from pharmaceuticals to plastics.

• Primary alkyl halides: Halogen is bonded to a carbon atom attached to only one other carbon atom.
• Secondary alkyl halides: Halogen is bonded to a carbon atom linked to two other carbon atoms.
• Tertiary alkyl halides: Halogen is attached to a carbon atom connected to three other carbon atoms.

Dialkyl Copper Reagents

Dialkyl copper reagents, often referred to as Gilman reagents, are a class of organocopper compounds commonly employed in organic synthesis to form carbon-carbon bonds. Typically formulated as \(( ext{R}_2 ext{CuLi})\), these reagents are prepared by treating organolithium compounds with copper(I) salts.

Dialkyl copper reagents are known for their mild reactivity which allows for selective transformations in complex molecules. These reagents are particularly useful in synthesis because they can replace halides in alkyl halides to form new alkane products, showcasing their utility in coupling reactions.

A critical aspect of dialkyl copper reagents is their ability to perform reactions at low temperatures, reducing the risk of unwanted side reactions. This attribute also helps in preserving sensitive functional groups in the molecules, thereby broadening their applicability in synthesizing fine chemicals and pharmaceuticals.

Organocopper Coupling Reactions

Organocopper coupling reactions, such as the Gilman reaction, play a pivotal role in the construction of carbon-carbon bonds in organic synthesis. These reactions involve the coupling of organocopper reagents, like the dialkyl copper reagents, with alkyl halides to form alkanes.

The process begins with the transfer of an alkyl group from the copper reagent to the alkyl halide. This transformation effectively replaces the halogen atom in the halide with the alkyl group from the Gilman reagent, resulting in the formation of an alkane. Such transformations are central to the synthesis of organic compounds, offering routes to complex molecular structures.

Key features of organocopper coupling reactions include:

• High selectivity in product formation, often leading to minimal side reactions.
• Effectiveness at low temperatures, which helps maintain functional group integrity.
• Applications in synthesizing intermediates for pharmaceuticals and natural products.

These traits make organocopper coupling reactions indispensable in creating new molecules for various industrial applications.