CH$_3$ - CH$_2$ - COOCH$_2$ - CH$_3$ From the condensed structure above, the reactants are

To solve this, we need to understand the structure of an ester and how it is formed through the process of esterification.

1. Analyze the structure

The given compound is: CH$_3$ - CH$_2$ - COOCH$_2$ - CH$_3$

An ester is formed by the reaction between a carboxylic acid and an alcohol. The general formula for an ester is R-COO-R', where:

• R-COO- comes from the carboxylic acid.
• -R' comes from the alcohol.

2. Break down the molecule

Let’s split the structure at the ester linkage (-COO-):

• Part 1 (Acid side): CH$_3$ - CH$_2$ - COO- • This part contains 3 carbon atoms (Propanoate). The corresponding acid is Propanoic acid (CH$_3$CH$_2$COOH).
• Part 2 (Alcohol side): -CH$_2$ - CH$_3$ • This part contains 2 carbon atoms. The corresponding alcohol is Ethanol (CH$_3$CH$_2$OH).

3. Explain the concept (Esterification)

Esterification is a condensation reaction where an acid and an alcohol react to form an ester and water:

In this specific case:

4. Identify the reactants

Looking at our breakdown:

• The acid part is Propanoic acid.
• The alcohol part is Ethanol.

Comparing this to your options, we see that Option D matches our findings perfectly.

5. Exam Tip

When naming or identifying esters, remember the "Alcohol-Acid" rule:

• The first part of the name (the alkyl group) comes from the alcohol (e.g., Ethyl from Ethanol).
• The second part of the name (the alkanoate) comes from the acid (e.g., Propanoate from Propanoic acid).
• Always look for the "COO" group; the carbon attached to the two oxygens is the "head" of the acid part!