Problem 137 - A Complete Resource Book in Chemistry for JEE Main

Question

The total number of isomers which are primary amines with a molecular formula \(\mathrm{C}_{4} \mathrm{H}_{7} \mathrm{~N}\), having no \(\mathrm{C} \equiv \mathrm{C}\) bond is

Step-by-Step Solution

Answer

The total number of primary amine isomers is 4.

Step 1: Understanding Primary Amines

Primary amines are compounds that contain an \(-\mathrm{NH}_2\) group attached to a carbon atom and have no carbon-carbon triple bond.

Step 2: Analyzing the Molecular Formula

The given molecular formula is \(\mathrm{C}_{4} \mathrm{H}_{7} \mathrm{~N}\), which implies 4 carbon atoms, 7 hydrogen atoms, and 1 nitrogen atom. There must also be a \(-\mathrm{NH}_2\) group involved.

Step 3: Drawing Carbon Chain Structures

Considering the given constraints, start with a straight 4-carbon alkyl chain (butyl) and replace one hydrogens by the \(-\mathrm{NH}_2\). Next, make branches where possible.

Step 4: Applying Constraints of No Triple Bonds

Ensure each drawn isomer has no triple bond by checking that all bonds are either single or double and that the number of hydrogens and nitrogens matches.

Step 5: Listing Possible Isomers

Identify possible isomeric structures: 1-butanamine, 2-butanamine, 2-methylpropanamine, and 1-methylpropan-2-amine. Consider different placements of the \(-\mathrm{NH}_2\) group.

Step 6: Counting Unique Isomers

Check each structure for uniqueness, ensuring each has a different connectivity, resulting in a total count of valid isomers. The distinct primary amines without \(\mathrm{C} \equiv \mathrm{C}\) bonds should be four.

Key Concepts

Primary Amines

Primary amines are organic compounds featuring a functional group, specifically an \(-\mathrm{NH}_2\) group, connected to a carbon atom. This type of amine is considered primary because the nitrogen is bonded to just one carbon chain or alkyl group. This differs from secondary and tertiary amines where the nitrogen bonds to two or three carbon chains, respectively. To identify and work with primary amines, it is crucial to remember:

• The nitrogen atom forms three bonds – one with the carbon chain and two with hydrogen atoms, resulting in the \(-\mathrm{NH}_2\) structure.
• Primary amines need one available position on the carbon atom to accommodate the \(-\mathrm{NH}_2\) group.
• The absence of a triple bond, such as \(\mathrm{C} \equiv \mathrm{C}\), distinguishes the class of primary amines discussed here.

Molecular Formula

A molecular formula provides a count of each type of atom present in a molecule. For example, the formula \(\mathrm{C}_{4}\mathrm{H}_{7}\mathrm{~N}\) indicates the molecule contains 4 carbon atoms, 7 hydrogen atoms, and 1 nitrogen atom. This formula is key to determining the structure of a compound and assessing how different components, like the \(-\mathrm{NH}_2\) group, may be arranged.

• The given formula suggests that beyond the habitual bonds expected within organic compounds, special attention should be given to how the \(-\mathrm{NH}_2\) group fits into the structure.
• Interpreting molecular formulas is an essential skill as it guides chemists in visualizing potential structures the compound can form.
• Determining placement and count of atoms precisely is central to drawing isomers safely.

Carbon Chain Structures

Carbon chain structures are the backbone of organic chemistry. They consist of interlinked carbon atoms that provide the framework for other groups, such as \(-\mathrm{NH}_2\), to attach. In molecules with the formula \(\mathrm{C}_{4}\mathrm{H}_{7}\mathrm{~N}\), understanding carbon chain arrangements is vital for identifying possible structural isomers.

• A straight chain refers to a linear sequence of carbon atoms without any branching.
• In branched chain structures, one or more carbon atoms form side chains that deviate from the main line.
• In exploring isomers, you would employ both straight and branched arrangements to identify different compounds possible under the constraints of the molecular formula.
• The absence of a triple bond further aids in narrowing down valid structural possibilities in carbon chains.

Chemical Isomers

Chemical isomers are compounds with identical molecular formulas but different structural forms. In the context of primary amines with a formula \(\mathrm{C}_{4}\mathrm{H}_{7}\mathrm{~N}\), it's possible to have multiple isomers where the arrangement of the carbon chain and location of the \(\mathrm{NH}_2\) group differ.

• Isomers play a crucial role in chemistry as they can exhibit remarkably different physical and chemical properties despite sharing the same types and numbers of atoms.
• By repositioning functional groups, like the \(\mathrm{NH}_2\) group, on different carbon atoms, various isomers arise.
• In this specific example, the unique isomers include 1-butanamine, 2-butanamine, 2-methylpropanamine, and 1-methylpropan-2-amine.
• Understanding isomerism is important for applications in drug design, materials science, and many chemical processes.