Question

question 1: Propose a synthesis of the compound below on the left from ethyl acetoacetate (ethyl 3-oxobutanoate). You may use any of the reagents in the table.

question 2:

Each of the compounds below is treated with a large molar excess of D₂O containing a catalytic amount of NaOD. When this is done all of the acidic hydrogens are exchanged for deuteriums. Indicate the number of hydrogens exchanged on each compound.

question 3: Indicate whether the compounds below undergo racemization when treated with aqueous acid or base.

Answer 1

Concepts and reason

Optical activity: optical activity is a property of rotation of the plane polarized light when passed through certain organic sample which has chiral center.

Acetoacetate ester synthesis: Conversion of ethyl Acetoacetate to ketone after alkylating the alpha carbon between 2 carbonyl groups.

When treating the chemical compound by ${{\rm{D}}_{\rm{2}}}{\rm{O}}$ with catalytic amount of ${\rm{NaOD}}$ , the hydrogen which is present near to the carbonyl group (alpha hydrogen) is more acidic and that will be exchanged with deuterium.

The conversion of optically active compound into optically inactive one is called as racemization. If the compound contains chiral center with alpha hydrogen present in the chiral center, then the compound will undergo racemization.

Fundamentals

The acidic hydrogen in the carbonyl compound:

In the above compound, the highlighted hydrogens are acidic hydrogens.

Racemization will occur in the compound:

Chiral center: It can be defined as in a molecule, where the carbon is bonded to four non identical substituents.

The formation of the given compound is shown below.

(1)

The reagents are

$\begin{array}{l}\\{\bf{Conversion - 1}}\,:{\bf{i}},\,{\bf{b}}\,\\\\{\bf{Conversion - 2}}\,:{\bf{i}},{\bf{e}}\,\\\\{\bf{Conversion - 3}}:\,{\bf{h}}.\\\end{array}$

(2)

Exchanged hydrogens are marked in red.

(3)

The compounds that undergo racemization are shown below.

Ans: Part 1

The letters of the reagents in order is given below:

${\bf{i}}\,{\bf{b}}\,{\bf{i}}\,{\bf{e}}\,{\bf{h}}.$

Part 2

Number of hydrogen exchanged in each compound is given below:

Part 3

The compound that undergoes racemization when treated with aqueous acid or base is given below: