Question

Explain the differences in the condensed structural formulas of propanal and propanoic acid.

Short answer

Propanal: CH₃CH₂CHO; Propanoic acid: CH₃CH₂COOH. Propanal has a formyl group, and propanoic acid has a carboxyl group.

Step-by-step solution

Identify Functional Groups

Propanal is an aldehyde, which means it has a formyl group (-CHO) at the end of the carbon chain. Propanoic acid is a carboxylic acid, which means it has a carboxyl group (-COOH) at the end of the carbon chain.

Write the Condensed Structural Formula for Propanal

Propanal has a three-carbon chain with a formyl group at one end. Its condensed structural formula is CH₃CH₂CHO.

Write the Condensed Structural Formula for Propanoic Acid

Propanoic acid has a three-carbon chain with a carboxyl group at one end. Its condensed structural formula is CH₃CH₂COOH.

Compare the Two Formulas

The key difference between the two formulas is the functional group at the end of the carbon chain. Propanal ends with -CHO, while propanoic acid ends with -COOH.

Key concepts

Propanal

Propanal is a simple aldehyde. Aldehydes are a class of organic compounds known for having a carbonyl group (C=O) bonded to at least one hydrogen atom. In the case of propanal, this carbonyl group is at the end of the three-carbon chain.

The condensed structural formula for propanal is CH₃CH₂CHO. This formula breaks down as:

• CH₃-: A methyl group at the start
• -CH₂-: A methylene group in the middle
• -CHO: The formyl group at the end

When you look at propanal, you will see it has a linear structure with no branching. This makes it easy to identify and also means it has certain physical properties, like being relatively soluble in water and having a distinctive pungent odor.

Propanoic Acid

Propanoic acid is a type of carboxylic acid. Carboxylic acids are characterized by having a carboxyl group (COOH). This group is made up of a carbonyl (C=O) and a hydroxyl group (OH) bonded to the same carbon atom.

For propanoic acid, the condensed structural formula is written as CH₃CH₂COOH:

• CH₃-: A methyl group at the beginning
• -CH₂-: A methylene group in the middle
• -COOH: The carboxyl group at the end

Carboxylic acids are known for their acidic properties, which come from the carboxyl group being able to donate a proton (H⁺) in solution. This gives propanoic acid, like other carboxylic acids, the ability to participate in acid-base reactions. Additionally, carboxylic acids tend to have higher boiling points due to the formation of strong hydrogen bonds.

Functional Groups

Functional groups are specific groups of atoms within molecules that determine the chemical properties of those molecules. In organic chemistry, recognizing functional groups is crucial for understanding how molecules will behave in different environments.

In this exercise, we looked at two functional groups:

• Formyl group (-CHO): This group is present in aldehydes like propanal. It consists of a carbonyl (C=O) bonded to a hydrogen atom.
• Carboxyl group (-COOH): Found in carboxylic acids like propanoic acid, this group includes both a carbonyl and a hydroxyl group bonded to the same carbon atom.

By identifying these functional groups, we can predict the reactivity and properties of molecules. For example, aldehydes (with a formyl group) are generally more reactive towards nucleophiles than ketones. Carboxylic acids (with a carboxyl group) are acidic and can participate in a variety of chemical reactions, including esterification and amide formation.