Question

Draw structural formulas for the following acids and esters: (a) 2 -methylhexanoic acid (b) pentyl butanoate (which has the odor of apricots) (c) octyl acetate (which has the odor of oranges)

Short answer

2-methylhexanoic acid is CH₃-CH(CH₃)-CH₂-CH₂-CH₂-COOH, pentyl butanoate is CH₃-CH₂-CH₂-COO-CH₂-CH₂-CH₂-CH₂-CH₃, octyl acetate is CH₃-COO-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-CH₃.

Step-by-step solution

Determine the Structural Formula for 2-Methylhexanoic Acid

**Identify the Name Components:** - The backbone is hexanoic acid, meaning six carbon atoms in a chain with a carboxylic acid group at one end. - The '2-methyl' indicates a methyl group (CH₃) is attached to the second carbon of the chain. **Draw the Structure:** 1. Start with a six-carbon chain. 2. Attach a carboxylic acid group (COOH) on the first carbon. 3. Attach a CH₃ group on the second carbon. **Structure:** CH₃-CH(CH₃)-CH₂-CH₂-CH₂-COOH.

Determine the Structural Formula for Pentyl Butanoate

**Identify the Name Components:** - 'Pentyl' refers to a five-carbon alkyl chain. - 'Butanoate' is the ester derived from butanoic acid, indicating a four-carbon fatty acid chain. **Draw the Structure:** 1. Write a four-carbon chain with a carbonyl (COO) group at one end. 2. Attach a five-carbon chain to the oxygen of the ester group. **Structure:** CH₃-CH₂-CH₂-COO-CH₂-CH₂-CH₂-CH₂-CH₃.

Determine the Structural Formula for Octyl Acetate

**Identify the Name Components:** - 'Octyl' indicates an eight-carbon alkyl chain. - 'Acetate' is derived from acetic acid, which contributes a two-carbon part to the ester. **Draw the Structure:** 1. Outline the acetate part: CH₃-COO. 2. Connect an eight-carbon chain to the oxygen of the carboxyl group. **Structure:** CH₃-COO-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-CH₃.

Key concepts

Carboxylic acids

Carboxylic acids are organic compounds characterized by the presence of a carboxyl group, which is \(-COOH\). This group comprises a carbonyl \( (C=O) \) and a hydroxyl \( (OH) \) group. Carboxylic acids are known for their acidic properties due to the ability of the hydrogen in the carboxyl group to dissociate as a proton \((H^+)\). When you see names like "hexanoic acid," this usually means there's a straight chain of carbon atoms with a carboxylic acid group at one end. In organic chemistry, these acids serve as a starting point for creating esters and other derivatives.

Key Characteristics:

• Soluble in water due to polar nature.
• Typically have higher boiling points than other types of oxygenated organic compounds.
• Can form hydrogen bonds due to the polar \(-OH\) group.

Examples of carboxylic acids include acetic acid in vinegar and citric acid in citrus fruits.

Esters

Esters are derived from carboxylic acids and alcohols through a process known as esterification, which involves removing a water molecule. These compounds are characterized by an ester group, which is represented as \(-COO-\). The name of an ester combines the alkyl group from the alcohol and the acid part from the carboxylic acid, often used in flavors and fragrances.

Ester Characteristics:

• Often have pleasant, fruity smells, thus used in perfumes and flavorings.
• Usually volatile, which makes them great for scents and flavors.
• They are less polar than carboxylic acids and do not form hydrogen bonds easily.

For example, pentyl butanoate has a fruity smell similar to apricots, while octyl acetate smells like oranges. Esters play a crucial role in the diversity of organic smells and have extensive industrial applications.

Structural formulas

Structural formulas in organic chemistry offer a detailed insight into the molecular layout of compounds, showing how atoms are arranged and bonded. This visual representation reveals not only the individual atoms but how they're connected through single, double, or triple bonds. A simple way to think of structural formulas is like a map for scientists, helping them understand a compound's behavior and reactions.

Important Elements of Structural Formulas:

• They show the precise arrangement of atoms, including all functional groups like \(-COOH\) for carboxylic acids and \(-COO-\) for esters.
• Help in predicting physical and chemical properties of organic compounds.
• Illustrations can be line structures, where each line represents a bond, simplifying large complex molecules into more readable formats.

Drawing the structural formula is like translating the compound’s name into a visual piece, capturing every vital functional group and connectivity, crucial in predicting the compound’s interaction and reactivity.