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Answer 1

QUESTION:

A compound has a molecular formula C₄H₆, when it is treated with excess hydrogen in presence of Ni-catalyst, a new compound is C₄H₁₀ is formed. When C₄H₆ is treated with ammonical silver nitrate a white precipiatate is formed. What is the structural formula of the given compound?

ANSWER:

• Structural formula of the given compound is CH₃ - CH₂ - C ≡ CH.

GIVEN:

• A compound has a molecular formula C₄H₆.

• When C₄H₆ is treated with excess hydrogen in presence of Ni-catalyst, a new compound is C₄H₁₀ is formed.

• When C₄H₆ is treated with ammonical silver nitrate a white precipiatate is formed.

TO FIND:

• Structural formula of the given compound.

EXPLANATION:

$\sf C_4H_6 + H_2(excess) \xrightarrow{Ni-catalyst}C_4H_{10}$

$\sf C_4H_{10} \ is \ n - Butane$

Only Alkynes on treating with excess Hydrogen will give Alkanes.

This is also an example of Addition reaction.

$\sf C_4H_6 + H_2 \xrightarrow{Ni-catalyst}C_4H_{8}$

$\sf C_4H_8+ H_2 \xrightarrow{Ni-catalyst}C_4H_{10}$

And the overall reaction is:

$\sf C_4H_6+ 2H_2 \xrightarrow{Ni-catalyst}C_4H_{10}$

Now C₄H₆ is treated with ammonical silver nitrate which gives a white precipitate.

Ammonical silver nitrate is also called Tolen's reagent and has the Molecular formula (AgNO₃ + NH₄OH)

Consider a alkyne R - CH ≡ CH.

R - C ≡ CH + AgNO₃ + NH₄OH → R - C ≡ C - Ag↓ + H₂O + NH₄NO₃

Here R - C ≡ C - Ag is the white precipate.

Likewise C₄H₆ on reaction with Ammonical silver nitrate gives a white precipitate as it is a alkyne.

CH₃ - CH₂ - C ≡ CH + AgNO₃ + NH₄OH → CH₃ - CH₂ - C ≡ C - Ag↓ + H₂O + NH₄NO₃

Here CH₃ - CH₂ - C ≡ C - Ag is the white precipate.

Also alkynes have a general formula CₙH₂ₙ₋₂

In C₄H₆ n value is 4.

C₄H₂₍₄₎₋₂ = C₄H₈₋₂

C₄H₂₍₄₎₋₂ = C₄H₆

Hence C₄H₆ is the alkyne of Structurual formula CH₃ - CH₂ - C ≡ CH.