Problem 48 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

Predict the nature of \(\mathrm{P}\) in the following reaction \(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{CCH}_{3} \frac{\mathrm{NaNH}_{2} \text { /inert solvent }}{\text { heat }}{\longrightarrow} \mathrm{P}\)

Step-by-Step Solution

Answer

P is an acetylide ion (RC≡C⁻) formed after deprotonation.

Step 1: Analyze the Reaction Conditions

The given reaction involves acetylene (CH_3C equiv CCH_3) treated with NaNH_2 in an inert solvent, under heat. NaNH_2 is a strong base that can deprotonate terminal alkynes, leading to the formation of acetylide ions.

Step 2: Deprotonation of Terminal Alkyne

In this step, NaNH_2 deprotonates the terminal alkyne - one of the hydrogen atoms from the H_3 group, specifically the hydrogen attached to the terminal carbon, is removed. This results in the formation of an acetylide ion, which is a strong nucleophile.

Step 3: Predict the Product

The formation of the acetylide ion, Cequiv C^-CH_3, does not result in additional subsequent reactions in the presence of only NaNH_2 and heat without further electrophiles or reactive species present. Thus, the immediate nature of P following this step is the acetylide ion itself.

Key Concepts

Deprotonation

Deprotonation is an important concept, especially in organic chemistry. It involves the removal of a proton (a hydrogen ion, H⁺) from a molecule. When a molecule loses a proton, it becomes negatively charged, often forming a conjugate base.

In the context of terminal alkynes, deprotonation is crucial for creating reactive intermediates, like acetylide ions. Alkyne deprotonation typically requires a strong base, and NaNH₂ (sodium amide) is commonly used because it can effectively remove the hydrogen atom from the terminal alkyne.

• NaNH₂ acts as a strong base, facilitating the removal of the proton from the alkyne.
• Deprotonation converts the alkyne into a more reactive form, which can be used in further chemical reactions.
• This process is essential for various synthesis reactions in organic chemistry.

Acetylide Ion

An acetylide ion is a highly reactive species formed when a terminal alkyne undergoes deprotonation. It is represented as a carbon-carbon triple bond attached to a negatively charged carbon atom \(R- ext{C} ext{≡} ext{C}^- \). The negatively charged carbon makes acetylide ions strong nucleophiles.

These ions are particularly useful in organic synthesis because they can create carbon-carbon bonds with various electrophiles.

• The acetylide ion generated from deprotonation is poised for further reactions.
• They can attack electrophilic centers, aiding in the formation of larger organic molecules.
• This ability makes them crucial for constructing complex structures in synthesis processes.

Due to their negative charge and high energy, acetylide ions must be handled carefully to avoid unwanted side reactions.

Terminal Alkyne

Terminal alkynes are a type of alkyne where the triple bond is located at the end of the carbon chain. These molecules are characterized by having a \(- ext{C≡C-H}\) group, which is crucial for undergoing deprotonation.

The unique position of the hydrogen atom in terminal alkynes makes them important in synthetic chemistry. The acidic hydrogen can be easily removed by strong bases such as NaNH₂, leading to different transitions.

• Terminal alkynes provide a versatile platform for generating acetylide ions.
• Their unique properties are leveraged in creating different organic compounds.
• They serve as starting materials in synthesizing complex molecules due to their reactivity.

Understanding terminal alkynes is vital for anyone studying organic chemistry, particularly those interested in synthesis and structural modifications of organic compounds.