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Ch.5 - Stereochemistry
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.5 - StereochemistryProblem 11
Chapter 5, Problem 11

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)?
(+)-carvone smells like caraway seed, (−)-carvone smells like spearmint.

Verified step by step guidance
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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.
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 (−).
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.
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.
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.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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.
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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.
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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.
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Related Practice
Textbook Question
One of the crowning achievements of natural products synthesis was Bryostatin 1, published by Professor Gary Keck (University of Utah; Journal of the American Chemical Society, 2011, 133, 744–747). The Bryostatins are a familyof compounds isolated from aquatic invertebrates known as Bryozoans. The compounds are of interest for a variety of biological effects, including anti-cancer activity and reversing brain damage in rodents.(d) How many chiral centers are in this molecule?(e) Using the number of chiral centers you reported in part(d), calculate the number of stereoisomers possible atthese chiral centers. (Ignore stereoisomers at double bonds.)
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Textbook Question
Write structural formulas for the following compounds (includes both old- and new-style names).(j) vinylacetylene(k) (S)-3-methyl-1-penten-4-yne
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Textbook Question

A chiral sample gives a rotation that is close to 180°. How can one tell whether this rotation is +180° or -180°?

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Textbook Question

A chemist finds that the addition of (+)-epinephrine to the catalytic reduction of butan-2-one (Figure 5-17 ) gives a product that is slightly optically active, with a specific rotation of +0.45°. Calculate the percentages of (+)-butan-2-ol and (−)-butan-2-ol formed in this reaction.

Textbook Question

When optically pure (R)-2-bromobutane is heated with water, butan-2-ol is the product. The reaction forms twice as much (S)-butan-2-ol as (R)-butan-2-ol. Calculate the e.e. and the specific rotation expected for the product.

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Textbook Question

A solution of 0.50 g of (−)-epinephrine (see Figure 5-16) dissolved in 10.0 mL of dilute aqueous HCl was placed in a 20-cm polarimeter tube. Using the sodium D line, the rotation was found to be −5.1° at 25 °C. Determine the specific rotation of epinephrine.

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