If you had the two enantiomers of carvone in unmarked bottles, could you use just your nose and a polarimeter to determine
a. whether it is the (+) or (−) enantiomer that smells like spearmint
b. whether it is the (R) or (S) enantiomer that smells like spearmint?
c. With the information given in the drawings of carvone above, what can you add to your answers to (a) and (b)?

Verified step by step guidance

1. Step 1: Analyze the given information about carvone enantiomers. The (+)-carvone enantiomer smells like caraway seed, while the (−)-carvone enantiomer smells like spearmint. This indicates that the smell is directly related to the enantiomeric form.
2. Step 2: Use a polarimeter to determine the optical activity of the carvone enantiomers. A polarimeter measures the direction and degree of rotation of plane-polarized light. The (+)-enantiomer rotates light clockwise (dextrorotatory), while the (−)-enantiomer rotates light counterclockwise (levorotatory). This will help identify whether the sample is (+) or (−).
3. Step 3: Relate the smell to the optical activity. Based on the information provided, the (−)-carvone enantiomer smells like spearmint, and the (+)-carvone enantiomer smells like caraway seed. By combining the polarimeter data and the smell, you can determine which enantiomer corresponds to spearmint.
4. Step 4: Determine the absolute configuration (R or S) of the enantiomers. The drawings provided show that the (+)-carvone enantiomer has the R configuration, while the (−)-carvone enantiomer has the S configuration. This means the spearmint smell corresponds to the (S)-carvone enantiomer.
5. Step 5: Summarize the findings. Using both the polarimeter and the smell, you can identify the enantiomer as either (+)-carvone (R configuration, caraway seed smell) or (−)-carvone (S configuration, spearmint smell). The drawings confirm the relationship between optical activity, absolute configuration, and smell.

Key Concepts

Enantiomers

Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. They have the same molecular formula and connectivity but differ in the spatial arrangement of atoms. This difference can lead to distinct physical properties, such as smell, as seen with (+)-carvone and (−)-carvone, which smell like caraway seed and spearmint, respectively.

Optical Activity

Optical activity refers to the ability of chiral compounds to rotate the plane of polarized light. This property is measured using a polarimeter, which quantifies the angle of rotation. Each enantiomer will rotate light in opposite directions; thus, a polarimeter can help distinguish between the (+) and (−) forms of carvone based on their specific rotations.

Chirality and R/S Nomenclature

Chirality is a property of a molecule that has a non-superimposable mirror image, often due to the presence of a chiral center, typically a carbon atom bonded to four different groups. The R/S nomenclature system is used to assign configurations to these chiral centers, helping to identify the specific enantiomer. Understanding this system is crucial for determining whether the enantiomer that smells like spearmint is (R) or (S) carvone.