Which class of compounds is usually associated with pleasant scents?

• A. Terpenes
• B. Alkaloids
• C. Amines
• D. Alcohols

Answer: (A)

Scent in plants and essential oils mainly comes from volatile terpene compounds. Terpenes are built from isoprene units and come in many forms, like monoterpenes and sesquiterpenes, which easily evaporate at room temperature. That volatility lets them waft into the air and create recognizable fragrances. The diversity of terpene structures gives a wide range of scents—from citrusy and fresh to piney and floral. For example, limonene gives a citrus note, pinene a piney scent, and linalool a floral aroma. Other classes—alkaloids tend to be bitter or toxic and aren’t typically associated with pleasant smells; amines and alcohols can have odors too, but they don’t define the broad, pleasant fragrance profile that terpenes do.