Question

The number of primary amines of formula \(\mathrm{C}_{4} \mathrm{H}_{11} \mathrm{~N}\) are (a) 2 (b) 3 (c) 4 (d) 5

Short answer

There are 4 primary amines possible for \(\mathrm{C}_{4}\mathrm{H}_{11}\mathrm{N}\).

Step-by-step solution

Understand the Formula

We want to find the number of primary amines with the molecular formula \(\mathrm{C}_{4}\mathrm{H}_{11}\mathrm{N}\). A primary amine has the structure \(\mathrm{RNH}_{2}\), where \(\mathrm{R}\) is an alkyl group derived from the \(\mathrm{C}_{4}\) hydrocarbon skeleton.

Determine Possible Alkyl Groups

Identify the possible structures for a \(\mathrm{C}_{4}\) hydrocarbon chain. These are butane and isobutane. Butane has a straight chain (\(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{CH}_{3}\)) and isobutane has a branched chain (\((\mathrm{CH}_{3})_{2}\mathrm{CHCH}_{3}\)).

Identify Primary Amines from Alkyl Groups

For each hydrocarbon structure, determine where the \(\mathrm{NH}_{2}\) group (the amine group) can be placed. For butane (straight chain), the \(\mathrm{NH}_{2}\) group can replace a hydrogen at either the terminal carbon or the second carbon. For isobutane, the \(\mathrm{NH}_{2}\) group can replace a hydrogen on a terminal carbon or the second carbon leading to different structures.

Count Unique Primary Amines

From butane, two primary amines can be made: butan-1-amine (\(\mathrm{NH}_{2}\) on the terminal carbon) and butan-2-amine (\(\mathrm{NH}_{2}\) on the second carbon). From isobutane, there are two possibilities as well: 2-methylpropan-1-amine and 2-methylpropan-2-amine. Another possibility is by placing the \(\mathrm{NH}_{2}\) on the tertiary carbon of isobutane, resulting in 2-amino-2-methylpropane. Thus, there are 4 primary amines.

Key concepts

Primary Amines

In organic chemistry, amines are a versatile class of compounds derived from ammonia by replacement of one or more of its hydrogen atoms by alkyl groups. Among amines, primary amines are particularly straightforward. They are characterized by having the general structure \( \text{RNH}_2 \), meaning they consist of an ammonia derivative with one hydrogen atom replaced by an alkyl group \( \text{R} \). Primary amines are the simplest type of amines and act as building blocks in organic synthesis.

Primary amines exhibit basic properties due to the lone pair of electrons on the nitrogen atom, which can accept a proton. Their functional group, \( \text{NH}_2 \), can form hydrogen bonds, affecting the compound's solubility and boiling point. These characteristics are crucial in determining where an amine can interact with other molecules, making them a pivotal point for many organic reactions.

Molecular Formula C4H11N

The molecular formula \( \text{C}_4\text{H}_{11}\text{N} \) suggests a compound containing four carbon atoms, eleven hydrogen atoms, and one nitrogen atom, typical of amines. This formula can potentially represent various isomers, primarily due to variations in the carbon skeleton and the position of the nitrogen atom.

By understanding the molecular formula, we can predict the types of chemical and physical properties the molecule may exhibit. For the molecular formula \( \text{C}_4\text{H}_{11}\text{N} \), we identify it as a primary amine, since there is one nitrogen atom that links with one alkyl group (the rest being hydrogen atoms). Thus, formulating different structural arrangements with the alkyl group \( \text{R} \) becomes key in identifying all possible primary amine structures.

Alkyl Groups

Alkyl groups play a central role in forming primary amines. They are hydrocarbon groups based on alkanes, where one hydrogen atom is removed, which allows them to attach to other atoms or groups of atoms. In our context, alkyl groups replace a hydrogen in ammonia (\( \text{NH}_3 \)) to form an amine.

In the given exercise, the main alkyl groups to consider are derived from butane and isobutane. Butane provides a straight-chain alkyl group, whereas isobutane gives a branched form. This distinction is crucial as it changes how and where the amine group \( \text{NH}_2 \) attaches. Such varying structures alter the connectivity and the resulting chemical properties of the amines. For example:

• Butane can lead to butan-1-amine and butan-2-amine.
• Isobutane can form 2-methylpropan-1-amine, 2-methylpropan-2-amine, and 2-amino-2-methylpropane.

Isomerism in Organic Chemistry

Isomerism is a fundamental concept in organic chemistry, where compounds with the same molecular formula have different arrangements of atoms. This typically leads to compounds with different chemical or physical properties.

In this exercise, the isomerism of the compound \( \text{C}_4\text{H}_{11}\text{N} \) is essential for identifying the number of primary amines. Structural isomers arise when atoms are arranged in different orders. For instance:

• With butane and isobutane as our starting points, the position of the \( \text{NH}_2 \) group can vary, leading to different isomers.
• Each position gives rise to a unique compound, such as butan-1-amine or 2-methylpropan-2-amine, due to variations in the connectivity of the carbon backbone.

Understanding isomerism allows chemists to explore the diversity of organic compounds, thus broadening the scope of chemical synthesis and application.