Question

There are four amine isomers with the molecular formula \(\mathrm{C}_{3} \mathrm{H}_{9} \mathrm{~N}\). Draw their condensed structural formulas. Name and classify each as a primary \(\left(1^{\circ}\right)\), secondary \(\left(2^{\circ}\right)\), or tertiary \(\left(3^{\circ}\right)\) amine.

Short answer

Propan-1-amine: primary, Isopropylamine: secondary, Ethyl(methyl)amine: secondary, Trimethylamine: tertiary.

Step-by-step solution

- Identify the molecular formula and possible structures

Given the molecular formula \(\text{C}_3\text{H}_9\text{N}\), we need to determine possible structures that fit this formula. Amines contain nitrogen atoms bonded to one or more carbon atoms.

- Draw the primary amine structure

The primary amine has one alkyl group attached to the nitrogen atom. One possible structure is: \(\text{CH}_3\text{CH}_2\text{CH}_2\text{NH}_2\). This is called propan-1-amine.

- Draw secondary amine structures

Secondary amines have two alkyl groups attached to the nitrogen atom. One structure is: \(\text{CH}_3\text{CH}(\text{NH}_2)\text{CH}_3\). This is called isopropylamine. Another structure could be: \(\text{CH}_3\text{NH}(\text{CH}_2\text{CH}_3)\). This is called ethyl(methyl)amine.

- Draw the tertiary amine structure

Tertiary amines have three alkyl groups attached to the nitrogen atom. One structure is: \(\text{CH}_3\text{N}(\text{CH}_3)(\text{CH}_3)\text{CH}_3\). This is called trimethylamine.

- Classify each amine

Propan-1-amine is a primary amine \(1^{\text{o}}\). Isopropylamine and ethyl(methyl)amine are secondary amines \(2^{\text{o}}\). Trimethylamine is a tertiary amine \(3^{\text{o}}\).

Key concepts

primary amine

A primary amine is an amine where the nitrogen atom is bonded to only one carbon atom and two hydrogen atoms. The simplest primary amine with the molecular formula \(\text{C}_3\text{H}_9\text{N}\) is propan-1-amine.
Its structural formula is: \(\text{CH}_3\text{CH}_2\text{CH}_2\text{NH}_2\).
In this molecule, the single nitrogen atom is bonded to one alkyl group (propyl group) and two hydrogen atoms.
This makes it a primary amine because it has the template: \(\text{R-NH}_2\), where \(\text{R}\) is an alkyl group.

Some features of primary amines include:

• primarily occur in simple organic compounds and in nature
• their reactivity is characterized by the lone pair of electrons on the nitrogen allowing them to act as nucleophiles.

Understanding primary amines is critical for mastering more complex organic chemistry concepts.

secondary amine

A secondary amine has its nitrogen atom bonded to two carbon atoms and one hydrogen atom.
The nitrogen in secondary amines has a lone pair of electrons and is connected to two alkyl groups.
For the molecular formula \(\text{C}_3\text{H}_9\text{N}\), two secondary amines exist:

• Isopropylamine (\text{CH}_3\text{CH}(\text{NH}_2)\text{CH}_3)
• Ethyl(methyl)amine (\text{CH}_3\text{NH}\text{CH}_2\text{CH}_3)

These structures differ in how the carbon chains are attached to the nitrogen atom.
Key features of secondary amines include:

• Tendency to form stable intermediates in substitution reactions.
• Reactivity similar to primary amines but forms different products due to additional alkyl groups.

The presence of two alkyl groups affects their physical properties, such as boiling points and solubility in water.

tertiary amine

A tertiary amine has the nitrogen atom bonded to three carbon atoms and no hydrogen atoms directly attached to the nitrogen.
An example with the molecular formula \(\text{C}_3\text{H}_9\text{N}\) is trimethylamine.
Its structural formula is: \(\text{(CH}_3\text{)}_3\text{N}\).
In this molecule, the nitrogen is bonded to three methyl groups, which makes it a tertiary amine.
Some general characteristics of tertiary amines are:

• They act as bases due to the lone pair of electrons on nitrogen
• Lack of hydrogen atoms on the nitrogen makes them less reactive in some organic reactions compared to primary and secondary amines

Understanding tertiary amines is essential to grasp the diversity and behavior of nitrogen-containing organic compounds.

molecular structures

Molecular structures of amines are critical for understanding their physical and chemical properties.
The molecular formula \(\text{C}_3\text{H}_9\text{N}\) can result in different isomers based on the arrangement of carbon, hydrogen, and nitrogen atoms.
Drawing the structures helps visualize how the nitrogen atom is bonded to other atoms.
Some basics of molecular structures:

• A primary amine structure has the template: \(\text{R-NH}_2\)
• A secondary amine structure has the template: \(\text{R'}\text{-N}(\text{R})\text{H}\)
• A tertiary amine structure has the template: \(\text{R'}\text{-N}(\text{R})(\text{R''})\)

These structures are crucial for predicting reactions and behaviors in organic compounds.
Always identify the number of carbon groups attached to the nitrogen to determine the class of amine.