Question

Draw structures corresponding to the following aldehyde and ketone names: (a) 3-Methylpentanal (b) 4-Chloro-2-hydroxybutanal (c) \(p\) -Methylbenzaldehyde (d) 2 -Ethylcycloheptanone (e) Cyclopropyl methyl ketone (f) Methyl phenyl ketone (also known as acetophenone)

Short answer

Draw the structures based on names, considering the main carbon backbone, substituents, and carbonyl group positions.

Step-by-step solution

Understand the components of the name

For aldheyde and ketone IUPAC names, the suffix `-al` indicates an aldehyde, while the suffix `-one` indicates a ketone. Identify and translate any prefixes detailing additional functional groups or branches.

Identify the parent chain or ring

For each compound, determine the main carbon chain or cyclic structure. For example, `3-Methylpentanal` has a five-carbon chain, while `2-Ethylcycloheptanone` contains a seven-membered ring.

Consider and add substitutes

Use the given prefixes to place substituents at the appropriate positions along the main carbon chain or ring. In `4-Chloro-2-hydroxybutanal`, place chlorine at carbon 4 and a hydroxyl group at carbon 2.

Place the carbonyl group

For aldehydes, the carbonyl group is at the end of the chain, while in ketones, it is typically placed at the lowest possible numbered carbon atom within the chain or ring. In `3-Methylpentanal`, the aldehyde group is at carbon 1.

Create the structure

Draw the skeleton of the molecule, placing each functional group and substituent into their correct positions based on previous steps.

Key concepts

Aldehydes

Aldehydes are organic compounds characterized by the presence of a carbonyl group (\(\text{C}=\text{O}\)) linked to a hydrogen atom. This distinctive group is typically placed at the end of a carbon chain. Aldehydes play a crucial role in chemistry, serving as key intermediates in various synthetic pathways.
The names of aldehydes in IUPAC nomenclature typically end with "-al". This ending indicates the presence of the aldehyde group. When naming aldehydes, it's important to identify the longest carbon chain that includes the aldehyde group.
Two common examples of aldehydes include:

• **3-Methylpentanal**: This is an aldehyde with a five-carbon chain. The chain is derived from pentane, with a methyl group on the third carbon.
• **4-Chloro-2-hydroxybutanal**: Here, "butanal" indicates a four-carbon chain aldehyde. The chlorine atom is at the fourth position, while a hydroxyl (−OH) group is at the second position.

Ketones

Ketones are characterized by a carbonyl group (\(\text{C}=\text{O}\)) that is bonded to two carbon atoms. Unlike aldehydes, the carbonyl group in ketones is never at the end of the carbon chain. Instead, it's found in the internal position, providing ketones their distinct structural property. These compounds are crucial in various chemical processes and are highly valued in industrial applications.
When naming ketones using IUPAC nomenclature, the suffix "-one" is utilized. The position of the carbonyl group is indicated by numbering the longest carbon chain such that the carbonyl carbon gets the lowest possible number.
Common ketones include:

• **2-Ethylcycloheptanone**: A seven-membered ring where the carbonyl group is bonded within the ring. The prefix "ethyl" indicates an ethyl group attached at the second carbon.
• **Methyl phenyl ketone**: Also known as acetophenone, this ketone features a methyl group and a phenyl group attached to the carbonyl carbon.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In organic chemistry, identifying functional groups is essential because they define the class to which the molecule belongs and its reactivity.
The carbonyl group (\(\text{C}=\text{O}\)) is an essential functional group for both aldehydes and ketones. In aldehydes, this group is linked to a hydrogen atom and is located at the end of the chain, while in ketones, it's bonded between carbon atoms within a carbon chain or ring.
Examples of other functional groups found in aldehydes and ketones include:

• **Hydroxyl group (-OH)**: Seen in compounds like 4-chloro-2-hydroxybutanal, where it contributes to the molecule's reactivity.
• **Chloro group (Cl-)**: Adds unique properties to the molecule such as in 4-chloro-2-hydroxybutanal, affecting its polarity and reactivity.

Carbon Chain

In organic molecules, a carbon chain serves as the molecule's backbone with various lengths influencing its properties. Understanding carbon chains is fundamental in predicting the molecule's behavior and in naming its structure using IUPAC nomenclature.
Terms like "pentanal" or "butanal" indicate a specific number of carbon atoms - five and four, respectively. The main chain should include the most significant functional groups, such as the aldehyde or carbonyl group.
Each carbon atom in the chain needs to be numbered, starting from the end nearest the functional group. This helps locate other substituents correctly. For example:

• In **3-Methylpentanal**, the main chain is pentane with a methyl substituent on the third carbon.
• In **4-Chloro-2-hydroxybutanal**, butanal is a four-carbon chain with designated functional groups and substituents.

Cyclic Structures

Cyclic structures are frequently encountered in organic chemistry. They are compounds where carbon atoms form a ring, which can significantly affect the compound's reactivity and physical properties.
These structures often contain functional groups such as ketones, which determine the chemical behavior of the molecule. Cyclic ketones, like **2-Ethylcycloheptanone**, have a carbonyl group within the ring itself.
Key aspects of cyclic structures include:

• **Ring Size**: Can vary with common ring sizes being 5, 6, or 7 carbon atoms, affecting the stability of the molecule.
• **Substituents**: Affect the chemical behavior and naming of cyclic compounds. For instance, ethylcycloheptanone indicates an ethyl group in the seven-membered ring structure.

Understanding cyclic structures involves identifying these attributes and knowing how they interact with functional groups to influence the molecular properties.