Question

Question: Draw the products formed when the following alkynes are treated with each set of reagents: [1] ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{,}{\mathbf{H}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}\mathbf{,}{\mathbf{HgSO}}_{\mathbf{4}\mathbf{}}\mathbf{;}\mathbf{}\mathbf{\left[}\mathbf{2}\mathbf{\right]}\mathbf{}{\mathbf{R}}_{\mathbf{2}}\mathbf{BH}\mathbf{}\mathbf{followed}\mathbf{}\mathbf{by}\mathbf{}{\mathbf{H}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{2}}\mathbf{,}{\mathbf{OH}}^{\mathbf{-}}$.

a.

b.

Short answer

Answer

a.

b.

Step-by-step solution

Step-by-Step Solution Step 1: Hydroboration-oxidation Reaction

Hydroboration-oxidation reaction involves the conversion of an alkyne to aldehyde or ketone. The reagents used is borane, peroxide and a hydroxyl ion source.

In case of internal alkyne, the final product formed is a ketone and in case of terminal alkynes, it is an aldehyde. The general reaction scheme is shown below:

General scheme of hydroboration-oxidation reaction

Hydration reaction

Similar to that of hydroboration-oxidation, in case of hydration, the hydrogen atom gets attached to the less substituted carbon of the terminal alkyne group. The final product of the reaction is a ketone.The general reaction scheme is shown below:

General scheme of hydration reaction

Determination of the type of bond present

The bonds are classified as ionic or covalent based on atomic charges. Two neutral atoms will form a covalent bond, whereas two charged species will form an ionic bond.

Reaction scheme

a.

Hydration and hydroboration reaction for a.

b.

Hydration and hydroboration reaction for b.