Question

The number of isomers of \(\mathrm{C}_{6} \mathrm{H}_{14}\) is (A) 6 (B) 5 (C) 4 (D) 7

Short answer

The number of isomers of \(\mathrm{C}_{6} \mathrm{H}_{14}\) is 5. This can be determined by listing all possible arrangements of the six carbon atoms while ensuring that each arrangement results in a total of 14 hydrogen atoms. The 5 unique isomers are: 1) Linear isomer, 2) 2-Methylpentane, 3) 3-Methylpentane, 4) 2,2-Dimethylbutane, and 5) 2,3-Dimethylbutane.

Step-by-step solution

Write down the molecular formula for hexane

The given compound, \(\mathrm{C}_{6}\mathrm{H}_{14}\), is an alkane with six carbon atoms. The general molecular formula for alkanes is \(\mathrm{C_nH_{2n+2}}\) where n is the number of carbon atoms. In this case, n = 6.

List all possible isomers

We will now list all possible isomers of \(\mathrm{C}_{6}\mathrm{H}_{14}\) by arranging the six carbon atoms and making sure that each arrangement results in a total of 14 hydrogen atoms: 1. Linear isomer: All six carbon atoms are connected in a straight chain. 2. 2-Methylpentane: A five-carbon chain with a methyl group (\(\mathrm{CH}_3\)) attached to the second carbon atom. 3. 3-Methylpentane: A five-carbon chain with a methyl group (\(\mathrm{CH}_3\)) attached to the third carbon atom. 4. 2,2-Dimethylbutane: A four-carbon chain with two methyl groups (\(\mathrm{CH}_3\)) attached to the second carbon atom. 5. 2,3-Dimethylbutane: A four-carbon chain with one methyl group (\(\mathrm{CH}_3\)) attached to the second carbon atom and another methyl group (\(\mathrm{CH}_3\)) attached to the third carbon atom. We find that there are no more possible isomers that result in the given molecular formula.

Count the isomers and find the answer

As we have identified above, there are 5 unique isomers for \(\mathrm{C}_{6}\mathrm{H}_{14}\). Therefore, the correct answer is (B) 5.

Key concepts

Structural Isomerism

Structural isomerism, a core concept in organic chemistry, occurs when molecules with the same molecular formula have their atoms bonded together in different orders, thereby creating distinct structures. This is a key concept to understand when exploring isomers of hexane (C6H14), as it accounts for the diversity of isomers possible for alkanes, such as hexane, despite having the same number of carbon and hydrogen atoms.

Considering hexane's molecular formula, C6H14, structural isomerism allows for multiple configurations. Each isomer features unique properties such as boiling points, melting points, and density that can drastically differ from the other isomers, despite having the identical molecular formula. This differentiation in isomers is crucial, as it affects how the compound behaves in reactions and in different environments. By understanding how to identify and distinctive structural isomers, students can tackle various organic chemistry problems with a deeper comprehension of molecular structures.

Alkane Isomers

Alkane isomers are a practical example of structural isomerism found among the simplest organic compounds, the alkanes. These hydrocarbons consist only of carbon and hydrogen atoms with single covalent bonds and follow the general formula \(C_nH_{2n+2}\), where 'n' is the number of carbon atoms.

In the case of hexane \(C6H14\), which is an alkane with six carbon atoms, the basic straight-chain structure is just the beginning. The carbon chain can be rearranged to form various branched structures, as long as the four valence electrons of each carbon atom are fully bonded. As a result, compounds such as 2-methylpentane, 3-methylpentane, and dimethylbutanes are formed, each representing a unique structural isomer of hexane. Exploring alkane isomers helps students understand how changed connectivity affects physical and chemical properties, a fundamental concept in organic chemistry.

Organic Chemistry Problems

Solving organic chemistry problems often involves understanding the concepts of isomerism, recognizing patterns in molecular structures, and drawing connections between structure and properties. When faced with a challenge such as determining the number of isomers for a given alkane, like hexane, a methodical approach is paramount.

Students must start with the molecular formula and recognize the necessary conditions for an alkane. They then enumerate all the reasonable structural variations, taking care to account for each possibility that differs in the order of atom connectivity without appearing identical through simple rotation or reflection. This step-by-step process enables students to apply concepts systematically to complex problems, enhancing their skills in tackling increasingly challenging organic chemistry exercises.