The problem presents a two-step reaction sequence and asks to identify the intermediate compound A and the reactant B. The starting material is propyne ( ), and the final products are a substituted alkyne (C) and sodium bromide ( ).
Concept Used:
The solution involves two key reactions in alkyne chemistry:
1. Formation of an Acetylide Anion: Terminal alkynes (alkynes with a hydrogen atom attached to a triply-bonded carbon) are weakly acidic. They can be deprotonated by a strong base, such as sodium metal ( ) or sodamide ( ), to form a sodium acetylide salt. In this reaction, the sodium acts as a reducing agent, producing the sodium salt and hydrogen gas.
2. Nucleophilic Substitution by an Acetylide Anion: The acetylide anion ( ) is a strong nucleophile. It can react with a primary alkyl halide in a nucleophilic substitution reaction (specifically, an reaction) to form a new carbon-carbon bond, resulting in a longer, internal alkyne.
Step-by-Step Solution:
Step 1: Determine the structure of compound A.
The first reaction is the reaction of propyne ( ) with sodium metal ( ). Propyne is a terminal alkyne, and the hydrogen atom on the terminal carbon is acidic. Sodium metal will deprotonate the alkyne to form a sodium propynide salt.
Therefore, the intermediate compound A is sodium propynide, .
Step 2: Determine the structure of compound B.
with a branch on the second carbon of the added chain. This is likely a typographical error in the problem's depiction of product C. Let's assume the product is the straight-chain alkyne (hex-2-yne), as would be formed from 1-bromopropane, which is a more common reactant in textbook examples and aligns with the options.
Assuming the product is hex-2-yne, the added group is (a propyl group). This would mean B is 1-bromopropane, . This matches the structure of B given in option (1).
Let's proceed by assuming the product shown has a typo and the intended product is . Reaction:
Final Computation & Result:
Step 3: Match the identified structures of A and B with the given options.
- Compound A is sodium propynide:
- Compound B is 1-bromopropane:
Let's evaluate the other options:
- Option (2): A is incorrect (propene), B is incorrect.
- Option (3): A is incorrect (propane), B is incorrect.
- Option (4): A is correct, but B is incorrect (propane).
The correct choice is (1) .
