Which of the following statements concerning organic compounds is false?
A. Compounds carrying the same functional group must have the same carbon framework. B. A functional group typically increases the melting and boiling points of the compound of which it is part. C. A functional group typically increases the solubility of the compound of which it is part. D. As an alkyl group increases in size, it decreases the solubility of the compound of which it is part. E. Compounds carrying the same functional group exhibit similar chemical and physical properties.
The correct answer and explanation is:
The false statement is A. Compounds carrying the same functional group must have the same carbon framework.
Explanation:
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. While functional groups define the reactivity and properties of organic compounds, the carbon framework (or structure) can vary, even for compounds that share the same functional group.
For example, consider the hydroxyl group (-OH). Alcohols have this functional group, but the carbon frameworks can differ. Ethanol (CH₃CH₂OH) and methanol (CH₃OH) both contain the hydroxyl group, yet they have different carbon backbones: ethanol has two carbon atoms, while methanol has just one. Despite this difference in structure, both compounds still exhibit the properties typical of alcohols, such as solubility in water and the ability to form hydrogen bonds.
Now, let’s discuss the other statements:
B. A functional group typically increases the melting and boiling points of the compound of which it is part.
This is generally true. Functional groups can influence the melting and boiling points of a compound due to their ability to engage in specific intermolecular interactions, such as hydrogen bonding, dipole-dipole interactions, or van der Waals forces. For instance, alcohols tend to have higher boiling points than alkanes of similar size due to hydrogen bonding.
C. A functional group typically increases the solubility of the compound of which it is part.
This is also true. The presence of functional groups can enhance the solubility of compounds in different solvents. For example, alcohols (with the -OH group) are more soluble in water than alkanes because the hydroxyl group forms hydrogen bonds with water molecules.
D. As an alkyl group increases in size, it decreases the solubility of the compound of which it is part.
This is correct. Alkyl groups are non-polar, and as their size increases, the molecule becomes more hydrophobic. This reduces the compound’s solubility in polar solvents, such as water.
E. Compounds carrying the same functional group exhibit similar chemical and physical properties.
This is generally true. Compounds that share the same functional group tend to exhibit similar reactivity and other physical properties like solubility, boiling point, and acidity. For example, both aldehydes and ketones have a carbonyl group and often show similar chemical reactivity, such as undergoing nucleophilic addition reactions.
In summary, while functional groups are crucial in determining the properties of organic compounds, the carbon framework is not necessarily the same for compounds with the same functional group.