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Question: An unknown compound \[(A)\]has a molecular formula \[{C_4}{H_6}.\]When \[(A)\]is treated with excess...

An unknown compound (A)(A)has a molecular formula C4H6.{C_4}{H_6}.When (A)(A)is treated with excess of Br2B{r_2} a new substance(B)(B) with formula C4H6Br4{C_4}{H_6}B{r_4} is formed. (A)(A) forms a white ppt. with ammoniacal silver nitrate solution.(A)(A) may be:
A. But-1-yne
B. But-2-yne
C. But-1-ene
D. But-2-ene

Explanation

Solution

C4H6{C_4}{H_6} is alkyne. Alkynes are unsaturated hydrocarbons having triple bonds between at least two adjacent carbon atoms.
It’s general formula is CnH2n−2{C_n}{H_{2n - 2}}

Complete step by step answer:
Let us form an equation according to the given condition

C4H6{C_4}{H_6}is butyne. It can either be But-1-yne or But-2-yne.
CH3−CH2−C≡CHC{H_3} - C{H_2} - C \equiv CH But-1-yne
CH3−C≡C−CH3C{H_3} - C \equiv C - C{H_3} But-2-yne
If the triple bond is present with the carbon atom 11 and 22, then the hydrogen atom is present at C-atom 11 so it is acidic in nature.
CH3−CH2−C≡CHC{H_3} - C{H_2} - C \equiv CHis acidic in nature.
Since Ammoniacal silver nitrate is reducing agent, it reduces butyne, and butyne oxidize ammonical silver nitrate solution.
We know that oxidation and Reduction occur together.
But-1-yne reduces by tollen’s reagent and form white precipitate
CH3−CH2−C≡C−H+C{H_3} - C{H_2} - C \equiv {C^ - }{H^ + }

So, the correct answer is “Option A”.

Additional Information:
Tollen’s Reagent is an ammoniacal solution of AgNO3AgN{O_3}. It is prepared by adding NH4OHN{H_4}OH solution toAgNO3AgN{O_3} solution till the precipitate of Ag2OA{g_2}O is formed which just gets dissolved. It has the formula [Ag(NO3)2]+OH−{[Ag{(N{O_3})_2}]^ + }O{H^{^ - }}
2AgNO3+2NH4OH→Ag2O+2NH4NO3+H2O2AgN{O_3} + 2N{H_4}OH \to A{g_2}O + 2N{H_4}N{O_3} + {H_2}O
Ag2O+4NH4OH→2[Ag(NH3)2]+OH−+H2OA{g_2}O + 4N{H_4}OH \to 2{[Ag{(N{H_3})_2}]^ + }O{H^ - } + {H_2}O
We can define oxidation and reduction as follows:
Addition of oxygen or removal of hydrogen is called Oxidation.
Addition of hydrogen or removal of oxygen is called Reduction.
Since But-1-yne is acidic in nature. So it can easily remove H-atoms and oxidates, while Tollen’s reagent reduces. But-2-yne does not have acidic hydrogen, so it will not react with tollen’s reagent.

Note:
Oxidation and reduction occurs simultaneously. This reaction is a Redox reaction in which But-1-yne reduces and Tollen’s reagent oxidises.