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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 14a,b
Chapter 5, Problem 14a,b

Make a model of each compound, draw it in its most symmetric conformation, and determine whether it is capable of showing optical activity.
a. 1-bromo-1-chloroethane
b. 1-bromo-2-chloroethane

Verified step by step guidance
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Step 1: Understand the concept of optical activity. A compound is optically active if it is chiral, meaning it lacks a plane of symmetry and has a non-superimposable mirror image. Chirality often arises when a carbon atom is bonded to four different groups.
Step 2: Analyze the structure of 1-bromo-1-chloroethane. Draw the molecule, ensuring that the carbon atom at position 1 is bonded to a bromine atom, a chlorine atom, a hydrogen atom, and a methyl group (-CH3). Check if this carbon atom is a chiral center by confirming that all four groups attached to it are different.
Step 3: Determine the symmetry of 1-bromo-1-chloroethane. Rotate the molecule in your mind or using a model to see if it has a plane of symmetry. If no plane of symmetry exists, the molecule is chiral and capable of optical activity.
Step 4: Analyze the structure of 1-bromo-2-chloroethane. Draw the molecule, ensuring that the carbon atoms at positions 1 and 2 are correctly substituted. Carbon 1 is bonded to a bromine atom, a hydrogen atom, and a -CH2Cl group, while carbon 2 is bonded to a chlorine atom, a hydrogen atom, and a -CH2Br group. Check if either carbon atom is a chiral center.
Step 5: Determine the symmetry of 1-bromo-2-chloroethane. Examine the molecule for a plane of symmetry or superimposability of its mirror image. If the molecule lacks a plane of symmetry and has at least one chiral center, it is capable of optical activity. Otherwise, it is not optically active.

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Key Concepts

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

Stereoisomerism

Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of those atoms. This can lead to different physical and chemical properties. Understanding stereoisomerism is crucial for determining whether a compound can exhibit optical activity, which is a key aspect of the question.
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Determining when molecules are stereoisomers.

Chirality

Chirality is a property of a molecule that makes it non-superimposable on its mirror image, much like left and right hands. A chiral molecule typically has at least one carbon atom bonded to four different substituents, creating two enantiomers. Identifying chiral centers in the given compounds is essential for assessing their potential for optical activity.
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What is chirality?

Optical Activity

Optical activity is the ability of a chiral compound to rotate the plane of polarized light. This property arises from the presence of chiral centers in the molecule. To determine if the compounds in the question can show optical activity, one must analyze their structures for chirality and the presence of enantiomers.
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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

Draw three-dimensional representations of the following compounds. Which have asymmetric carbon atoms? Which have no asymmetric carbons but are chiral anyway? Use your models for parts (a) through (d) and any others that seem unclear.

(c)

(d)

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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

Draw three-dimensional representations of the following compounds. Which have asymmetric carbon atoms? Which have no asymmetric carbons but are chiral anyway? Use your models for parts (a) through (d) and any others that seem unclear.

(e)

(f)

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Textbook Question

Draw three-dimensional representations of the following compounds. Which have asymmetric carbon atoms? Which have no asymmetric carbons but are chiral anyway? Use your models for parts (a) through (d) and any others that seem unclear.

(a)

(b)

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