Organic Chemistry MCAT Practice Exam

Which feature characterizes conjugated systems?

1. Weak colors

2. Strong colors

3. High molecular weight

4. Low stability

The correct answer is: Strong colors

Conjugated systems are characterized by a series of alternating single and multiple bonds, which allows for the delocalization of π (pi) electrons across the atoms involved. This delocalization is significant because it lowers the energy of the system, contributing to its stability and imparting specific optical properties. One of the most notable features of conjugated systems is their ability to absorb visible light, which is ultimately linked to the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). As the conjugation length increases, the energy gap decreases, allowing the system to absorb light at longer wavelengths. This phenomenon results in conjugated compounds often exhibiting strong colors. In contrast, systems with weak colors typically arise in compounds with lower levels of conjugation or without any significant delocalization of electrons. Therefore, the statement about strong colors fits well because it emphasizes how the presence of conjugation can lead to pronounced and vivid coloration due to effective light absorption.