Question

The compound cyclohexane is an alkane in which six carbon atoms form a ring. The partial structural formula of the compound is as follows: (a) Complete the structural formula for cyclohexane. (b) Is the molecular formula for cyclohexane the same as that for \(n\) -hexane, in which the carbon atoms are in a straight line? If possible, comment on the source of any differences. (c) Propose a structural formula for cyclohexanol, the alcohol derived from cyclohexane.

Short answer

The complete structural formula for cyclohexane is: ``` H H H | | | H--C--C--C--H | | | C-----C-----C | H H H ``` The molecular formula for cyclohexane is \(C_6H_{12}\) and for n-hexane is \(C_6H_{14}\). The difference arises due to the ring structure of cyclohexane, which has two fewer hydrogen atoms compared to n-hexane. The structural formula for cyclohexanol, derived from cyclohexane, is: ``` H H H | | | H--C--C--C--H | | | C-----C-----C | H H O-H \ H ```

Step-by-step solution

a. Complete the structural formula for cyclohexane

To draw the complete structural formula for cyclohexane, we need to show all the carbon atoms (C) in a ring and fill in the missing hydrogen atoms (H) to follow the bonding patterns of an alkane. Alkanes have single bonds between the carbon and hydrogen atoms, and each carbon atom forms four bonds in total. In a cyclohexane ring, the carbon atoms naturally form single bonds with each other. To complete the structure, add the missing hydrogen atoms to make sure that each carbon atom has 4 bonds. Here is the complete structural formula for cyclohexane: ``` H H H | | | H--C--C--C--H | | | C-----C-----C | H H H ```

b. Comparing molecular formulas for cyclohexane and n-hexane

First, we need to determine the molecular formula for both cyclohexane and n-hexane. The molecular formula shows the composition of the molecule by listing the number of atoms in it. In this case, we are interested in the quantities of carbon (C) and hydrogen (H) atoms. For cyclohexane, we have 6 carbon atoms and 12 hydrogen atoms, so its molecular formula is \(C_6H_{12}\). Now, let's consider the structure of n-hexane. As a straight-chain alkane, n-hexane has a chain of 6 carbon atoms, with each carbon atom having 2 hydrogen atoms and the terminal carbon atoms having an additional 3 hydrogen atoms. This gives us a total of 6 carbon atoms and 14 hydrogen atoms. Therefore, the molecular formula for n-hexane is \(C_6H_{14}\). Comparing the two formulas, we can see that they are different, with cyclohexane having two fewer hydrogen atoms than n-hexane. The difference arises due to the ring structure of cyclohexane, removing the need for two additional hydrogen atoms that would be present in a straight-chain alkane like n-hexane.

c. Proposing a structural formula for cyclohexanol

Cyclohexanol is the alcohol derived from cyclohexane. In the context of organic chemistry, alcohols are compounds that contain a hydroxyl group (-OH) bonded to a carbon atom. The hydroxyl group replaces one of the hydrogen atoms of the parent alkane (in this case, cyclohexane). To draw the structural formula for cyclohexanol, we start with the cyclohexane structure and replace one hydrogen atom with a hydroxyl group (-OH). Here is a possible structural formula for cyclohexanol: ``` H H H | | | H--C--C--C--H | | | C-----C-----C | H H O-H \ H ``` In this structure, one of the hydrogen atoms in the cyclohexane ring has been replaced with a hydroxyl group, forming cyclohexanol.

Key concepts

Alkanes

Alkanes are a class of hydrocarbons that are chemically composed of carbon (C) and hydrogen (H) atoms connected by single bonds. They are the simplest form of hydrocarbons and follow the general molecular formula \( C_nH_{2n+2} \) for acyclic members. Alkanes are known for being saturated, meaning that all carbon-carbon bonds are single, with no room for additional hydrogen atoms, making them relatively stable compounds.
Alkanes can be divided into different categories based on their structure:

• Straight-chain alkanes: Where carbon atoms are connected in a continuous line, without any branching. An example is n-hexane.
• Branched-chain alkanes: These have alkyl groups branching off from the main carbon chain.
• Cyclic alkanes: These have carbon atoms arranged in a ring, as seen in cyclohexane.

Cyclohexane, being a cyclic alkane, has carbon atoms forming a closed loop, which impacts its chemical properties, such as having fewer hydrogen atoms compared to its straight-chain counterparts like n-hexane.

Molecular formula

A molecular formula provides insight into the number and types of atoms present in a compound. It serves as a simplified representation that reveals the elemental composition, crucial for understanding the chemical nature of substances.
For cyclohexane, the molecular formula is \( C_6H_{12} \). This formula indicates that the molecule consists of six carbon atoms and twelve hydrogen atoms. The fewer hydrogen atoms in cyclohexane compared to n-hexane (whose formula is \( C_6H_{14} \)) can be attributed to its ring structure. As such, fewer hydrogen atoms are needed to satisfy the bonding requirements.
Molecular formulas help in predicting various chemical properties and play a significant role in chemical nomenclature and reactions.

Cyclohexanol

Cyclohexanol is an example of an organic compound known as an alcohol, characterized by the presence of a hydroxyl group (-OH) bonded to a carbon atom. This group is the defining feature of alcohols, distinguishing them from other hydrocarbons.
In cyclohexanol, the structure begins with cyclohexane as the base molecule. One of the hydrogen atoms in the cyclohexane ring is replaced by a hydroxyl group, creating the structure of cyclohexanol. This modification alters its chemical characteristics, imparting properties typical of alcohols such as polarity and the ability to form hydrogen bonds.
Cyclohexanol has uses in the manufacturing of various products, including nylon, and serves as a solvent in chemical industries. Understanding the transformation from cyclohexane to cyclohexanol sheds light on functional group modifications commonly observed in organic chemistry.