A Level Chemistry OCR Practice Exam

What is the role of a functional group in organic chemistry?

1. To define the overall molecular weight

2. To allow identification of isomer types

3. To dictate the chemical reactions that the molecule can undergo

4. To determine the solubility of the compound

The correct answer is: To dictate the chemical reactions that the molecule can undergo

In organic chemistry, a functional group is a specific group of atoms or bonds within a molecule that is responsible for the characteristic chemical reactions of that molecule. The presence of a functional group determines how the molecule will interact with others, which reactions it can undergo, and the types of transformations it can experience during a chemical process. For example, the hydroxyl group (-OH) found in alcohols makes them reactive in dehydration and oxidation reactions, while carboxylic acids (-COOH) can undergo acid-base reactions. By influencing the reactivity and behavior of organic compounds, functional groups play a critical role in their chemistry. This is why the correct answer emphasizes that the functional group dictates the chemical reactions that the molecule can undergo. The other options touch on different aspects of chemistry but do not accurately represent the primary role of functional groups. For example, while functional groups may indirectly influence molecular weight and solubility, they do not define the molecular weight directly, nor are they used specifically for classifying isomers. The classification of isomers can be based on structural differences that may or may not involve functional groups. Additionally, while solubility can be affected by the functional groups present, determining solubility is more complex and influenced by several factors