Question

Draw structures for all the alcohols with molecular formula \(\mathrm{C}_{6} \mathrm{H}_{14} \mathrm{O}\).

Short answer

Answer: There are a total of 8 distinct structures for alcohols with the molecular formula \(\mathrm{C}_{6}\mathrm{H}_{14}\mathrm{O}\). Their names are 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 3-methyl-1-pentanol, 3-methyl-2-pentanol, and 2,2-dimethyl-1-propanol.

Step-by-step solution

Identify the carbon skeletons

To start, we will identify all possible carbon skeletons (carbon chains) with 6 carbons that can hold the hydroxyl group. We have the following possibilities: 1. A straight chain with 6 carbons (hexane): \(\mathrm{C}-\mathrm{C}-\mathrm{C}-\mathrm{C}-\mathrm{C}-\mathrm{C}\) 2. A branched chain with 5 carbons and one methyl group (isopentane): \(\mathrm{C}-(\mathrm{C}-\mathrm{C})-\mathrm{C}-\mathrm{C}-\mathrm{C}\) 3. A branched chain with 4 carbons and two methyl groups (neopentane): \(\mathrm{C}-(\mathrm{C}-\mathrm{C}-\mathrm{C})-\mathrm{C}\)

Assign hydroxyl groups to carbon skeletons

Now, we will place the hydroxyl group on each of these carbon skeletons, while taking care to avoid repeating any structures. For the hexane skeleton: 1. 1-hexanol: -OH on the first carbon 2. 2-hexanol: -OH on the second carbon 3. 3-hexanol: -OH on the third carbon For the isopentane skeleton: 4. 2-methyl-1-pentanol: -OH on the first carbon 5. 2-methyl-2-pentanol: -OH on the second carbon 6. 3-methyl-1-pentanol: -OH on the carbon next to the methyl group 7. 3-methyl-2-pentanol: -OH on the carbon two away from the methyl group For the neopentane skeleton: 8. 2,2-dimethyl-1-propanol: -OH on the carbon at the center (not on the methyl groups) These are all the possible structures for alcohols with the molecular formula \(\mathrm{C}_{6}\mathrm{H}_{14}\mathrm{O}\), without any duplicates or enantiomers.

Key concepts

Carbon Skeleton Structures

Exploring the carbon skeleton structures is the initial step when analyzing compounds such as alcohols with the formula \(\mathrm{C}_6\mathrm{H}_{14}\mathrm{O}\). A 'carbon skeleton' refers to the chain or framework of carbon atoms that form the backbone of an organic molecule. The carbon atoms can be arranged in a variety of ways, leading to different structural possibilities for the compound.

For instance, a straight chain carbon skeleton consists of carbon atoms connected in a row without any branches. This is the simplest form and offers a starting point for developing more complex structures. However, complexity increases as we introduce branches in the skeleton by adding side chains, such as methyl (-CH₃) groups, transforming a straight chain into a branched chain. As we move from hexane to isopentane and neopentane structures, we rearrange the carbon atoms to create branched configurations.

In the given problem, we discuss three primary carbon skeleton configurations for the formula \(\mathrm{C}_6\mathrm{H}_{14}\mathrm{O}\)—hexane, isopentane, and neopentane. The placement of substituents like hydroxyl groups will vary depending on these skeletons, leading to different alcohols.

Alcohol Functional Group

The alcohol functional group significantly defines the properties of alcohol molecules and is represented by a hydroxyl (-OH) group. This group consists of an oxygen atom bonded to a hydrogen atom, and it is usually attached to a carbon atom within an organic compound.

In an alcohol molecule such as those with the composition \(\mathrm{C}_6\mathrm{H}_{14}\mathrm{O}\), the hydroxyl group must be placed on a carbon atom in the carbon skeleton. It is the position of this -OH group on the carbon chain that distinguishes one alcohol from another. For example, if the -OH is on the first carbon of a hexane chain, the resulting alcohol is named 1-hexanol. When the placement of the hydroxyl group changes to the second or third carbon, the compounds are named differently to represent their structures, such as 2-hexanol and 3-hexanol respectively.

The functionality that the -OH group brings is twofold: it influences the molecular geometry and the chemical reactivity of the compound, granting alcohols their characteristic physical and chemical properties.

Structural Isomerism

Structural isomerism is a fascinating aspect of organic chemistry, where molecules share the same molecular formula but differ in the arrangement of their atoms or functional groups. When we look at alcohols with the molecular formula \(\mathrm{C}_6\mathrm{H}_{14}\mathrm{O}\), the number of isomers becomes particularly significant due to the varied positions the -OH group can occupy, along with the potential for different carbon skeleton arrangements.

An essential rule in identifying structural isomers is to ensure no repeats in the created structures. Isomers should be unique in their connectivity. For example, placing the hydroxyl group on the second or third carbon of a hexane chain results in distinct alcohols, namely 2-hexanol and 3-hexanol. The situation is compounded with branched structures like isopentane and neopentane, which allow even more variations by altering the position of the -OH group relative to the branching.

As illustrated in the exercise, each different arrangement obtains a specific name to accurately describe the structure, emphasizing the importance of isomerism in determining the identity and properties of chemical compounds. Structural isomerism showcases the incredible diversity that can arise from a single molecular formula, leading to multiple unique structures, each with potentially different character and reactivity.