Problem 84 - Chemistry: The Central Science

Question

(a) What do ethane and ethanol have in common? (b) How does 1-propanol differ from propane?

Step-by-Step Solution

Answer

(a) Ethane and ethanol both have a carbon chain consisting of two carbon atoms. (b) 1-Propanol has an alcohol functional group (-OH) attached to the first carbon atom in the chain and contains an oxygen atom in addition to carbon and hydrogen atoms, while propane is part of the alkane group and is composed solely of carbon and hydrogen atoms.

Step 1: Write the chemical formulas of ethane and ethanol, 1-propanol, and propane

Ethane: \(C_2H_6\) Ethanol: \(C_2H_5OH\) 1-Propanol: \(C_3H_7OH\) Propane: \(C_3H_8\)

Step 2: Compare ethane and ethanol

Both ethane and ethanol have two carbon atoms in their molecular structure. They belong to different functional groups, with ethane being part of the alkane group and ethanol belonging to the alcohol group. The primary difference between them is that ethane has a single bond between the two carbon atoms and is composed solely of carbon and hydrogen atoms. In contrast, ethanol has an alcohol functional group (-OH) attached to one of the carbon atoms. The commonality between ethane and ethanol is the carbon chain consisting of two carbon atoms.

Step 3: Compare 1-propanol and propane

Both 1-propanol and propane have three carbon atoms in their molecular structure. Like ethane, propane belongs to the alkane group and is composed solely of carbon and hydrogen atoms. Its structure consists of a three-carbon chain with single bonds between the carbon atoms and all remaining valences satisfied by hydrogen atoms. 1-Propanol, on the other hand, has an alcohol functional group (-OH) attached to the first carbon atom in the chain. Unlike propane, 1-propanol contains an oxygen atom in addition to carbon and hydrogen atoms. The difference between the two compounds lies in the functional group (alcohol in 1-propanol) and the presence of an oxygen atom in 1-propanol's molecular structure.

Key Concepts

Functional Groups

Functional groups are distinct groups of atoms within molecules that determine the chemical behavior of those molecules. They are the key to understanding how different organic compounds react and interact with each other.
Some of the most common functional groups include:

• Alkanes: As a basic structure, alkanes are simply chains of carbon atoms bonded with hydrogen atoms. They are saturated hydrocarbons with single covalent bonds and no functional groups.
• Alcohols: These contain the hydroxyl group (-OH) attached to their carbon chain.

Functional groups like the alcohol group in ethanol and 1-propanol are critical because they modify the physical and chemical properties of the compound. This leads to various applications and reactivity patterns, making functional groups indispensable in organic chemistry.

Alkanes

Alkanes are the simplest type of hydrocarbons and are also known as paraffins. They consist exclusively of carbon and hydrogen atoms, with all the carbon-to-carbon bonds being single bonds. These single bonds categorize alkanes as saturated hydrocarbons.
Common properties of alkanes include:

• They are nonpolar molecules, making them relatively unreactive.
• Alkanes typically exhibit low boiling and melting points, which increase with the molecular size due to van der Waals forces.
• Since they lack functional groups, their reactions are mostly limited to combustion and substitution reactions.

Ethane, for instance, is an alkane with the molecular formula \(C_2H_6\), possessing a simple structure of two carbon atoms and six hydrogen atoms. Alkanes serve as a backbone for more complex chemical structures when functional groups are added.

Alcohols

Alcohols are a vital class of organic compounds characterized by having one or more hydroxyl groups (-OH) bonded to a carbon atom. This functional group dramatically changes the properties of the molecule compared to alkanes.
Some key features of alcohols include:

• They are generally more polar than alkanes due to the presence of the hydroxyl group, leading to higher solubility in water.
• Alcohols have higher boiling points than comparable alkanes due to hydrogen bonding.
• The hydroxyl group is responsible for the alcohol's ability to participate in reactions such as oxidation and dehydration.

Ethanol \(C_2H_5OH\), for example, is an alcohol with a similar backbone to ethane. However, the presence of the -OH group adds unique properties, influencing the molecule's reactivity and polarity. Similarly, 1-propanol \(C_3H_7OH\) differs from propane (an alkane) due to the hydroxyl group addition, which is crucial for its behavior in chemical reactions.