Question

Draw the structure of each carboxylic acid or ester. \begin{equation}\begin{array}{l}{\text { a. pentanoic acid }} \\ {\text { b. methyl hexanoate }} \\ {\text { c. } 3 \text { -ethylheptanoic acid }} \\\ {\text { d. butyl ethanoate }}\end{array}\end{equation}

Short answer

a. A five-carbon chain with a COOH group. b. A six-carbon chain with COO linked to a methyl group. c. A seven-carbon chain with a carboxyl group on one end and an ethyl group on the third carbon. d. A two-carbon chain with COO linked to a four-carbon chain.

Step-by-step solution

Drawing Pentanoic Acid

To draw pentanoic acid, we start with a chain of five carbon atoms for the 'pent' prefix. We need a carboxyl group (COOH) to make it a carboxylic acid. Attach the carboxyl group at the end of the chain to complete the structure.

Drawing Methyl Hexanoate

Methyl hexanoate is an ester. It is derived from hexanoic acid (which has six carbons) and methanol. Draw a six-carbon chain with a single oxygen double-bonded to the first carbon for the ester group (COO), and then draw a single carbon (methyl group) attached to the oxygen.

Drawing 3-Ethylheptanoic Acid

This is a carboxylic acid with a seven-carbon chain, indicated by 'heptanoic'. We need to add an ethyl group (–CH2CH3) on the third carbon of the chain. Attach the carboxyl group (COOH) at the end to complete the structure.

Drawing Butyl Ethanoate

Butyl ethanoate is an ester made from butanol and ethanoic acid. Draw an ethanoic acid portion (two carbons with a COO group), and attach a butyl group, a four-carbon chain, to the oxygen of the COO group.

Key concepts

Drawing Organic Compounds

Organic chemistry often requires visualizing the structure of compounds, which involves drawing molecules with various functional groups. To draw organic compounds accurately, one begins by identifying the base carbon chain, numbering the longest carbon chain to find the correct position for any substituents. Substituents are atoms or groups of atoms attached to the main chain, and they can significantly alter the physical and chemical properties of the compound.

When drawing, one should depict all carbon and hydrogen atoms, or choose a simplified representation like a skeletal structure where the carbon-to-carbon bonds are shown as lines and the carbon atoms are not explicitly drawn. Understanding how to draw these structures aids in visual comprehension and communication within the field of chemistry.

Functional Groups in Organic Chemistry

Functional groups are specific clusters of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They are the reactive part of the molecule and dictate properties like solubility, acidity, basicity, and reactivity.

In the context of carboxylic acids and esters, the functional groups are the carboxyl group (-COOH) and the ester group (-COO-), respectively. The carboxyl group is composed of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group (OH), while an ester group features a carbon double-bonded to an oxygen and single-bonded to another oxygen atom, which is in turn bonded to a carbon chain or a hydrogen atom.

Molecular Representation of Carboxylic Acids

Carboxylic acids are represented molecularly by the presence of a carboxyl group (-COOH) attached to a hydrocarbon chain. The length and branching of the chain, along with the presence of other functional groups, define the specific carboxylic acid.

The molecular representation can be shown in different forms like full structural formula, condensed formula, or skeletal formula, depending on the level of detail desired. In these formulas, the carboxyl group is usually denoted at the end of the hydrocarbon chain, signifying its terminal position, and establishing the molecule's acidic nature.

Esterification Process

Esterification is a chemical reaction in which a carboxylic acid reacts with an alcohol to form an ester and water. It is a subset of condensation reactions, where two molecules or parts thereof combine, releasing a small molecule, often water.

The process involves the nucleophilic attack of the alcohol's hydroxyl oxygen on the carbonyl carbon of the acid, followed by the loss of a water molecule. This reaction typically requires an acidic catalyst to proceed at a useful rate. Esters are commonly represented by their fruity or floral scents and are used in a wide range of products, from plastics to perfumes.