Question

Draw the structural formula for each of the following. a. formaldehyde (methanal) b. 4 -heptanone c. 3 -chlorobutanal d. \(5,5-\) dimethyl- 2 -hexanone

Short answer

a. Methanal: \( \ce{H-C(=O)-H} \) b. 4-heptanone: \( \ce{CH3-CH2-CH2-(C(=O))-CH2-CH2-CH3} \) c. 3-chlorobutanal: \( \ce{H-C(=O)-CH2-CH(Cl)-CH3} \) d. 5,5-dimethyl-2-hexanone: \( \ce{CH3-CH2-(C(=O))-CH2-(C(CH3)_2)- CH2-CH3} \)

Step-by-step solution

a. Formaldehyde (methanal)

Formaldehyde is also known as methanal, which indicates it has one carbon atom and is an aldehyde. Aldehydes have the functional group \( \ce{-CHO} \). To draw the structure, we simply connect the functional group to the single carbon atom. Methanal: \( \ce{H-C(=O)-H} \)

b. 4 -heptanone

Heptanone indicates that it has a ketone functional group \(\ce{C(=O)}\) and its carbon chain has 7 carbon atoms. The number 4 in front of the name shows the location of the ketone on the carbon chain. We will start by drawing the 7-carbon long chain and then add the ketone group to the 4th carbon atom. 4-heptanone: \( \ce{CH3-CH2-CH2-(C(=O))-CH2-CH2-CH3} \)

c. 3 -chlorobutanal

3-chlorobutanal indicates it is an aldehyde with a 4-carbon long chain with a chlorine atom attached at carbon number 3. First, draw the 4-carbon long chain and add the aldehyde functional group \( \ce{-CHO} \) to the end of the chain. Then add a chlorine atom to the 3rd carbon in the chain. 3-chlorobutanal: \( \ce{H-C(=O)-CH2-CH(Cl)-CH3} \)

d. 5,5- dimethyl-2-hexanone

5,5-dimethyl-2-hexanone is a ketone with 6 carbon atoms in the parent chain, the ketone group is at position 2 and there are two methyl groups at the 5th carbon atom. Start by drawing the 6-carbon long chain and then add the ketone group to the 2nd carbon. Lastly, add the two methyl groups to the 5th carbon. 5,5-dimethyl-2-hexanone: \( \ce{CH3-CH2-(C(=O))-CH2-(C(CH3)_2)- CH2-CH3} \)

Key concepts

Structural Formula

Understanding the structural formula is essential in organic chemistry as it represents how atoms are arranged and bonded in a molecule. It's like a blueprint for molecules, showing each atom connected to others by lines representing chemical bonds. This is crucial because different arrangements, even with the same atoms, can lead to entirely different properties and types of molecules.

For instance, in the structural formula of methanal (formaldehyde), the single carbon atom is connected to two hydrogen atoms and an oxygen atom, displaying a clear picture of its chemical structure as \( \ce{H-C(=O)-H} \).

Key aspects of structural formulas include:

• Showing the type and number of each atom
• Representing the specific bonds between them
• Indicating the molecule's three-dimensional arrangement

Practicing drawing structural formulas is a helpful skill for grasping complex organic molecules. It allows you to predict the molecule's reactivity and behavior.

Aldehydes

Aldehydes are an important class of organic compounds characterized by the presence of the functional group \( \ce{-CHO} \). This group contains a carbon atom double-bonded to an oxygen atom (carbonyl group) and also bonded to a hydrogen atom, making them distinct. Aldehydes are known for their role in various chemical reactions and their unique aromas, often used in perfumes and flavorings.

In the example of 3-chlorobutanal, you can see the aldehyde's \( \ce{-CHO} \) group attached at the end of a four-carbon chain, with a chlorine atom on the third carbon: \( \ce{H-C(=O)-CH2-CH(Cl)-CH3} \).

This indicates:

• The presence of an aldehyde functional group \( \ce{-CHO} \)
• The relative simplicity of its structure with varying carbon chain lengths
• The localization of substituents like chlorine, affecting physical and chemical properties

Aldehydes play a central role in many biochemical and industrial processes, making them an essential topic in organic chemistry.

Ketones

Ketones are another vital group of organic compounds, similar to aldehydes but with a slight difference in structure. They contain a carbonyl group \( \ce{C=O} \) bonded to two other carbon atoms. This position distinguishes them as compounds with the carbonyl group within the carbon skeleton, rather than at the edge like aldehydes. Their carbonyl group's internal placement often leads to unique reactivity patterns.

In 4-heptanone, the ketone group is placed on the fourth carbon in a seven-carbon-long chain: \( \ce{CH3-CH2-CH2-(C(=O))-CH2-CH2-CH3} \).

This arrangement reflects:

• The typical internal placement of the carbonyl group
• The diversity of molecules with the ketone functional group due to differing chain lengths and positions
• The variance in properties and uses based on specific ketone structures

Ketones, like aldehydes, serve distinct roles in both synthetic and natural processes, forming the basis for many compounds used in everyday life.

Functional Groups

Functional groups are specific groups of atoms within molecules that have particular reactive properties. They are the key players that define the characteristics and types of chemical reactions that the molecule can undergo. Think of them as the active centers of molecules.

Both aldehydes and ketones have the carbonyl group \( \ce{C=O} \), but its placement determines the type:

• Aldehydes have it at the end of the molecule \( \ce{-CHO} \)
• Ketones have it placed within the carbon chain \( \ce{C=O} \)

These functional groups' presence influences the molecule's polarity, solubility, and reactivity patterns.

Understanding functional groups is crucial for predicting how a molecule might interact with others, forming the basis for the study of reactivity and synthesis in organic chemistry. Recognizing these groups in various compounds is fundamental for mastering organic chemistry.