Which of the following compounds is not a stereoptene?

• A. Methyl Salicylate
• B. Menthol
• C. Camphor
• D. Thymol

Answer: (A)

Stereopenes are odor-active molecules whose smelling properties depend on their three-dimensional arrangement, meaning you need a chiral or otherwise stereochemically distinct form to have different enantiomers or diastereomers with different scents. Methyl salicylate is an achiral ester; it has no stereocenter, so there aren’t mirror-image forms to taste or smell differently. Menthol, camphor, and thymol, on the other hand, involve stereochemical features that give rise to distinct forms with their own olfactory notes or sensory effects. Menthol is famously chiral with enantiomers that differ in smell and coolness; camphor is optically active, and thymol also has stereochemical forms that influence its odor. So the compound that cannot be a stereoptene is methyl salicylate.