Question

Write a structural formula for each of the following compounds. a. methyl pentyl ketone b. 3-methylpentanal c. 2 -methyl- 1 -pentanol d. 1,2,3 -propanetriol e. 2 -methyl- 3 -hexanone

Short answer

a. \(CH_3CO(CH_2)_3CH_3\) b. \(CH_3CH_2CH(CH_3)CH_2CHO\) c. \(CH_2OHCH(CH_3)(CH_2)_3H\) d. \(HOCH_2CH(OH)CH_2OH\) e. \(CH_3CH(CH_3)CO(CH_2)_2CH_3\)

Step-by-step solution

Identify the functional group

Methyl pentyl ketone is a ketone, which means it has a carbonyl group, C=O.

Determine the carbon chain length and branching

The "pentyl" in the name indicates a 5-carbon chain, and "methyl" indicates a 1-carbon branch attached to the ketone.

Draw the structure

Connect the 5-carbon chain with the carbonyl group and the methyl branch like so: \(CH_3CO(CH_2)_3CH_3\) #b. 3-methylpentanal#

Identify the functional group

This compound is an aldehyde, meaning it has a formyl group, CHO, at the end of its carbon chain.

Determine the carbon chain length and branching

The "pent-" in the name indicates a 5-carbon chain, and "3-methyl" indicates a methyl branch connected to the third carbon atom.

Draw the structure

Connect the 5-carbon chain with the formyl group and the methyl branch at the third carbon like this: \(CH_3CH_2CH(CH_3)CH_2CHO\) #c. 2-methyl-1-pentanol#

Identify the functional group

This compound has an alcohol functional group, which contains an OH group.

Determine the carbon chain length and branching

The "pent-" in the name indicates a 5-carbon chain, and "2-methyl" indicates a methyl branch connected to the second carbon atom.

Draw the structure

Connect the 5-carbon chain with the alcohol group at the first carbon and the methyl branch at the second carbon like this: \(CH_2OHCH(CH_3)(CH_2)_3H\) #d. 1,2,3-propanetriol#

Identify the functional group

This compound has three alcohol groups, which contain OH groups.

Determine the carbon chain length and branching

The "propane-" in the name indicates a 3-carbon chain without any other branching.

Draw the structure

Connect the 3-carbon chain with the three alcohol groups at each of the carbon atoms like this: \(HOCH_2CH(OH)CH_2OH\) #e. 2-methyl-3-hexanone#

Identify the functional group

This compound is a ketone, which means it has a carbonyl group, C=O.

Determine the carbon chain length and branching

The "hexan-" in the name indicates a 6-carbon chain, and "2-methyl" indicates a methyl branch connected to the second carbon atom.

Draw the structure

Connect the 6-carbon chain with the carbonyl group at the third carbon and the methyl branch at the second carbon like this: \(CH_3CH(CH_3)CO(CH_2)_2CH_3\)

Key concepts

Functional Groups in Organic Chemistry

Functional groups are specific groups of atoms within molecules that determine the characteristic chemical reactions of those molecules. These groups are the key to understanding organic compound behavior and their interactions.

Common Functional Groups

• Alcohols: Contain an -OH group (e.g., ethanol, propanol).
• Aldehydes: Have a carbonyl group (C=O) bonded to at least one hydrogen atom (e.g., formaldehyde, acetaldehyde).
• Ketones: Feature a carbonyl group bonded to two carbon atoms (e.g., acetone, butanone).
• Carboxylic Acids: Have a carboxyl group (-COOH) (e.g., acetic acid, butyric acid).
• Ethers: Consist of an oxygen atom connected to two alkyl or aryl groups (e.g., diethyl ether).
• Esthers: Derived from a carboxylic acid and an alcohol (e.g., ethyl acetate).
• Amines: Contain a nitrogen atom bonded to alkyl or aryl groups (e.g., methylamine, aniline).

Each functional group has a specific nomenclature and properties that can be understood and predicted. Recognizing these groups makes it possible to draw and understand complex organic structures.

Drawing Organic Molecules

The ability to draw organic molecules is crucial for understanding their structure and properties. The steps below outline how to draw molecules accurately.

Basic Steps for Drawing Molecules

1. Identify the backbone of the molecule, which is the longest carbon chain or ring structure.
2. Add any functional groups and branches at their appropriate locations along the backbone.
3. Fill in the remaining hydrogen atoms, ensuring each carbon has four bonds.

For example, when drawing a ketone like methyl pentyl ketone, one must add the carbonyl functional group (C=O). Positioning and notation are crucial in demonstrating the molecule's structure clearly. Labels such as '2-methyl' provide insight into the placement of branches, indicating that a methyl group is attached to the second carbon in the chain. Clear, accurate diagrams help to visualize molecular interactions and are a foundational skill in organic chemistry.

IUPAC Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) nomenclature is a standardized method for naming organic chemical compounds. This system ensures that each compound has a unique and universally recognized name.

IUPAC Naming Basics

• Determine the longest carbon chain to establish the base name of the compound.
• Identify and name all functional groups and branches.
• Number the carbon atoms in the main chain to give the lowest possible numbers to the functional groups and branches.
• Combine prefixes, infixes, and suffixes according to the rules. Infixes often indicate the saturation or unsaturation of the carbon chain (e.g., 'an' for alkanes, 'en' for alkenes).

For instance, '3-methylpentanal' indicates a five-carbon aldehyde with a methyl group on the third carbon. Understanding IUPAC rules is essential not only for accurate communication but also for predicting the structure and properties of organic molecules based on their names.