Stereochemistry | Practice Problems, Examples & Solutions

Chirality

Introduction to General, Organic and Biochemistry

Using only $\mathrm{C}, \mathrm{H},$ and $\mathrm{O},$ write structural formulas for the lowest-molecular-weight chiral molecule of each class.
(a) Alkane
(b) Alkene
(c) Alcohol
(d) Aldehyde
(e) Ketone
(f) Carboxylic acid

Chirality: The Handedness of Molecules

06:00

Introduction to General, Organic and Biochemistry

There are eight primary amines with the molecular formula $\mathrm{C}_{3} \mathrm{H}_{13} \mathrm{N}$
(a) Name and draw a structural formula for each amine.
(b) Which of these amines are chiral?

Amines

09:45

Introduction to General, Organic and Biochemistry

Answer true or false.
(a) The $c$ is and trans stereoisomers of 2 -butene are achiral.
(b) The carbonyl carbon of an aldehyde, ketone, carboxylic acid, or ester cannot be a stereocenter.
(c) Stereoisomers have the same connectivity of their atoms.
(d) Constitutional isomers have the same connectivity of their atoms.
(e) An unmarked cube is achiral.
(f) A human foot is chiral.
(g) Every object in nature has a mirror image.
(h) The most common cause of chirality in organic molecules is the presence of a tetrahedral carbon atom with four different groups bonded to it.
(i) If a molecule is not superposable on its mirror image, the molecule is chiral.

Chirality: The Handedness of Molecules

(R) and (S) Nomenclature of Asymmetric Carbon Atoms

5 Practice Problems

14:08

Organic Chemistry

Threonine has two asymmetric centers and, therefore, has four stereoisomers. Naturally occurring L-threonine is $(2 S, 3 R)$ -threonine. Which of the following stereoisomers is $L$ -threonine?

Amino Acids, Peptides, and Proteins

01:40

Organic Chemistry

Does the following compound have the $R$ or the $S$ configuration?

Isomers: The Arrangement of Atoms in Space

02:08

Organic Chemistry

a. Do the following compounds have any asymmetric carbons?
1. $\mathrm{CH}_{2}=\mathrm{C}=\mathrm{CH}_{2} \quad$ 2. $\mathrm{CH}_{3} \mathrm{CH}=\mathrm{C}=\mathrm{CHCH}_{3}$
b. Are they chiral? (Hint: Make models.)

Stereochemistry

Optical Activity

29 Practice Problems

02:08

Chemistry

(a) A plane of symmetry in a molecule is a plane passing through the middle of the molecule that bisects the molecule into two mirror-image halves. If a molecule has a plane of symmetry, it cannot be chiral and cannot be optically active. Which of the following have at least one plane of symmetry? Do any have more than one?
(b) Specify the relationships (constitutionally isomeric or stereoisomeric) among these compounds.

Organic Chemistry

04:23

General Chemistry: Principles and Modern Applications

Compound $A$ is an alcohol of formula $C_{5} H_{12} O$ that can be resolved into enantiomers.(a) Draw three possible structures of compound A.
(b) Treatment of A with $\mathrm{CrO}_{3} /$ pyridine gives compound $\mathrm{B},$ which also exhibits optical activity. What are the structural formulas of $A$ and of $B ?$ Name and draw the enantiomers of A and B.

Structures of Organic Compounds

00:44

General Chemistry: Principles and Modern Applications

A sample of $(S)-C H_{3} C H_{2} C H\left(C H_{3}\right) C l$ is hydrolyzed by water, and the resulting solution is optically inactive.
(a) Write the formula of the product. (b) By which nucleophilic substitution reaction mechanism does this reaction occur?

Reactions of Organic Compounds

Biological Discrimination of Enantiomers

0 Practice Problems

Racemic Mixtures

8 Practice Problems

06:38

Organic Chemistry

A racemic mixture of 2-methyl-1-phenyl-1-butanone is formed when ( $R$ )-2-methyl-1-phenyl-1-butanone is dissolved in an acidic or basic aqueous solution. Give an example of another ketone that undergoes acid- or base-catalyzed racemization.

Reactions at the $\alpha$ -Carbon

02:06

Organic Chemistry

Reaction of HBr with $(R)-3$ -methyl-3-hexanol leads to racemic 3 -bromo3-methylhexane. Explain. (EQUATION CAN'T COPY)

Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations

06:53

Organic Chemistry

What products are formed from acid-catalyzed hydration of racemic ( $\pm$ )-4-methyl1-hexene? What can you say about the relative amounts of the products? Is the product mixture optically active?

Alkenes: Reactions and Synthesis

Enantiomeric Excess and Optical Purity

4 Practice Problems

02:39

Introduction to General, Organic and Biochemistry

Each of the following molecules has one stereocenter marked by an asterisk. Draw three-dimensional representations for the enantiomers of each molecule.

Chirality: The Handedness of Molecules

01:58

Organic Chemistry

Is the following compound optically active?

Isomers: The Arrangement of Atoms in Space

01:52

Organic Chemistry

Explain why the following compounds are not optically active:
a. the product obtained from the reaction of 1,3 -butadiene with cis -1,2-dichloroethene
b. the product obtained from the reaction of 1,3-butadiene with trans-1,2-dichloroethene

Delocalized Electrons and Their Effect on Stability, $\mathrm{p} K_{\mathrm{a}}$, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene"

Chirality of Conformationally Mobile Systems

2 Practice Problems

06:53

Organic Chemistry

The chair conformer of fluorocyclohexane is $0.25 \mathrm{kcal} / \mathrm{mol}$ more stable when the fluoro substituent is in an equatorial position than when it is in an axial position. How much more stable is the anti conformer than a gauche conformer of 1-fluoropropane, considering rotation about the $\mathrm{C}-1-\mathrm{C}-2$ bond?

An Introduction to Organic Compounds: Nomenclature, Physical Properties, and Structure

08:00

Organic Chemistry

Classify each of the following objects as to whether it is chiral or achiral:
(a) A screwdriver
(d) A tennis shoe
(g) A car
(b) A baseball bat
(e) An car
(h) A hammer
(c) A golf club
(f) A woodscrew

Stereochemistry

Chiral Compounds Without Asymmetric Atoms

7 Practice Problems

07:22

Organic Chemistry

a. For conjugated systems with two, three, four, five, six, and seven conjugated $\pi$ bonds, construct quick MOs (just draw the lobes at the ends of the conjugated system as they are drawn on pages 1220 and 1221 ) to show whether the HOMO is symmetric or antisymmetric.
b. Using these drawings, convince yourself that the Woodward-Hoffmann rules in Table 28.1 are valid.

Pericyclic Reactions

01:15

Organic Chemistry

Draw the structure for a compound with molecular formula $\mathrm{C}_{2} \mathrm{H}_{2} \mathrm{I}_{2} \mathrm{F}_{2}$.
a. that is optically inactive because it does not have an asymmetric center.
b. that is optically inactive because it is a meso compound.
c. that is optically active.

Isomers: The Arrangement of Atoms in Space

01:53

Organic Chemistry

a. Stereoisomers with two asymmetric carbons are called ______ if the configuration of both asymmetric carbons in one isomer is the opposite of the configuration of the asymmetric carbons in the other isomer.
b. Stereoisomers with two asymmetric carbons are called ______ if the configuration of both asymmetric carbons in one isomer is the same as the configuration of the asymmetric carbons in the other isomer.
c. Stereoisomers with two asymmetric carbons are called _______ if one of the asymmetric carbons has the same configuration in both isomers and the other asymmetric carbon has the opposite configuration in the two isomers.

Stereochemistry

Fischer Projections

17 Practice Problems

02:01

Biochemistry

Without consulting chapter figures, draw Fischer projection formulas for glycine, aspartate, leucine, isoleucine, methionine, and threonine.

Amino Acids and the Peptide Bond

00:30

Biochemistry

Following are Fischer projections for a group of five-carbon sugars, all of which are aldopentoses. Identify the pairs that are enantiomers and the pairs that are epimers. (The sugars shown here are not all of the possible five-carbon sugars.)

Carbohydrates

05:42

Introduction to General, Organic and Biochemistry

Draw Fischer projections for the product formed by treating each of the following monosaccharides with sodium borohydride, $\mathrm{NaBH}_{4}$, in water
(a) $D$ -Galactose
(b) D-Ribose

Carbohydrates

Diastereomers

23 Practice Problems

01:26

Introduction to General, Organic and Biochemistry

Consider the experimental antiviral drug Peramivir, shown below, a neuraminidase inhibitor recently supported by the U.S. Department of Health and Human Services as a treatment for Influenza A (H1N1), "Swine Flu."
(a) What is the molecular formula of Peramivir?
(b) Identify the functional groups labeled with arrows in the structure above. If any alcohols or amines are present, determine if they are primary, secondary, or tertiary.
(c) How many stereocenters are present in Peramivir?
(d) Determine the maximum number of stereoisomers possible for this molecule.
(e) Fill in the blanks: There is/are ______ enantiomer(s) and _______ diastereomer(s) of Peramivir.

Carboxylic Anhydrides, Esters, and Amides

01:36

Introduction to General, Organic and Biochemistry

(a) Find all of the carbon stereocenters in a cholesterol molecule.
(b) How many total stereoisomers are possible?
(c) How many of these stereoisomers do you think are found in nature?

Lipids

04:54

Introduction to General, Organic and Biochemistry

Consider $L u$ nesta, a nonbenzodiazepine hypnotic agent (i.e., sleep-inducing drug) that is frequently advertised on TV commercials. Answer the following questions with respect to the given structure:
(a) Determine the molecular formula for Lunesta.
(b) Identify the functional groups present in Lunesta.
(c) How many of Lunesta's rings are aromatic?
(d) Fill in the blanks as shown: Lunesta has stereocenter(s) and therefore possible stereoisomer(s). Of the possible stereocenter(s), is/are $R$ and is/are $S$.
(e) Does Lunesta have an enantiomer? Does it have a diastereomer?
(f) Which of the following is true about an enantiomer of Lunesta? Identify all that apply:
(1) The enantiomer rotates plane-polarized light in the opposite direction as Lunesta.
(2) The enantiomer is a mirror image of Lunesta.
(3) The enantiomer has the opposite biological effects as Lunesta (i.e., it keeps you awake).
(4) Lunesta does not have an enantiomer.
(g) Draw an enantiomer of Lunesta.
(h) Examine the derivative of the representation of the six-membered ring found in Lunesta. Draw the alternative chair conformations of this ring and label the more stable chair conformation. (Chapter 11 )

Chirality: The Handedness of Molecules

Stereochemistry of Molecules with Two or More Asymmetric Carbons

29 Practice Problems

05:45

Introduction to General, Organic and Biochemistry

Many tumors of the breast are correlated with estrogen levels in the body. Drugs that interfere with estrogen binding have antitumor activity and may even help prevent tumor occurrence. A widely used antiestrogen drug is tamoxifen.
(a) Name the functional groups in tamoxifen.
(b) Classify the amino group in tamoxifen as primary, secondary, or tertiary.
(c) How many stereoisomers are possible for tamoxifen?
(d) Would you expect tamoxifen to be soluble or insoluble in water? In blood?

Amines

02:59

Chemistry

In each of the following pairs, specify whether the two structural formulas represent constitutional isomers, cis, trans-stereoisomers, enantiomers, resonance structures, or are simply a different representation of the same structure.

Organic Chemistry

04:17

Chemistry

Define the term chiral. What are enantiomers?

Organic Chemistry

Meso Compounds

2 Practice Problems

05:21

Organic Chemistry

Which compounds are meso compounds?

Stereochemistry

Meso Compounds

Absolute and Relative Configuration

4 Practice Problems

02:03

Inorganic Chemistry

Which of the following square-planar complexes have 16-electron valence configurations?
a. $\operatorname{Ir}(\mathrm{CO}) \mathrm{Cl}\left(\mathrm{PPh}_{3}\right)_{2}$
b. $\operatorname{Rh} \mathrm{Cl}\left(\mathrm{PPh}_{3}\right)_{3}$
c. $\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}$
d. $c i s-\mathrm{PtCl}_{2}\left(\mathrm{NH}_{3}\right)_{2}$

Organometallic Chemistry

06:55

Introduction to General, Organic and Biochemistry

Glucose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6},$ contains an aldehyde group but exists predominantly in the form of the cyclic hemiacetal shown here. We will discuss this cyclic form of glucose in Chapter 20.
A cyclic hemiacetal is formed when the $-$ OH group of one carbon bonds to the carbonyl group of another carbon.
(a) Which carbon in glucose provides the $-\mathrm{OH}$ group and which provides the $-$ CHO group?
(b) Draw the alternative chair confirmations of $\beta-$ D-glucose and state which of the two is the more stable.

Aldehydes and Ketones

05:36

Introduction to General, Organic and Biochemistry

Consider the structure of the immunosuppressant $F K-506,$ a molecule shown to disrupt calcineurinmediated signal transduction in $T$ -lymphocytes.
(a) What is the molecular formula of this immunosuppressant?
(b) How many stereocenters are present in $F K-506 ?$ Determine the maximum number of stereoisomers possible.
(c) Identify and label the various functional groups present.
(d) Consider the two stereocenters in this structure labeled with asterisks ("). Determine the absolute configuration of each stereocenter.
(e) $F K-506$ has been shown to exhibit moderate solubility in various organic solvents. Is this immunosuppressant expected to be soluble in ethanol $\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\right) ?$
(f) Consider the carbon atom labeled "1." Describe the geometry and approximate bond angles about this carbon atom.
(g) Draw the alternative chair conformations of the cyclohexane ring at the lower right of $F K-506$ and label the more stable conformation.
(h) Are there any aromatic components present in $F K-506 ?$
(i) Patients taking $F K-506$ have reported several side effects from this medication, including headaches, nausea or diarrhea, and slight shaking. Would you expect the enantiomer of this drug to result in the same side effects?

Chirality: The Handedness of Molecules

Physical Properties of Diasteromers

0 Practice Problems

Resolution of Enantiomers

7 Practice Problems

01:08

Organic Chemistry

a. Using the wedge-and-dash notation, draw the nine stereoisomers of 1,2,3,4,5,6 -hexachlorocyclohexane.
b. From the nine stereoisomers, identify one pair of enantiomers.
c. Draw the most stable conformer of the most stable stereoisomer.

Isomers: The Arrangement of Atoms in Space

01:50

Organic Chemistry

When $\mathrm{Br}_{2}$ adds to a cis alkene that has different substituents attached to each of the two $s p^{2}$ carbons, such as cis-2-heptene, identical amounts of the two threo enantiomers are obtained even though $\mathrm{Br}^{-}$ is more likely to add to the less sterically hindered carbon of the bromonium ion. Explain why identical amounts of the two enantiomers are obtained.

The Reactions of Alkenes • The Stereochemistry of Addition Reactions

00:42

Organic Chemistry as a Language

Draw the enantiomer of each of the following compounds.
IMAGE IS NOT AVAILABLE TO COPY

CONFIGURATIONS

Drawing Enantiomers

Isomerism

5 Practice Problems

05:23

Organic Chemistry

a. Draw three constitutional isomers with molecular formula $\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}$.
b. How many constitutional isomers can you draw for $\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}$ ?

Isomers: The Arrangement of Atoms in Space

01:54

Organic Chemistry

Compare the physical properties of the three stereoisomers of 1,3-dimethylcyclopentane.
a. How do the boiling points of $\textbf{A}$ and $\textbf{B}$ compare? What about $\textbf{A}$ and $\textbf{C}$?
b. Characterize a solution of each of the following as optically active or optically inactive: pure $\textbf{A}$; pure $\textbf{B}$; pure $\textbf{C}$; an equal mixture of $\textbf{A}$ and $\textbf{B}$; an equal mixture of $\textbf{A}$ and $\textbf{C}$.
c. A reaction forms a 1 :1 :1 mixture of $\textbf{A}$, $\textbf{B}$, and $\textbf{C}$. If this mixture is distilled, how many fractions would be obtained? Which fractions would be optically active and which would be optically inactive?

Stereochemistry

Physical Properties of Stereoisomers

01:27

Organic Chemistry

Classify each pair of compounds as constitutional isomers or stereoisomers.

Stereochemistry

The Two Major Classes of Isomers

Enantiomers and diasteriomers

33 Practice Problems

03:13

Introduction to General, Organic and Biochemistry

Draw Fischer projections for all 2-ketopentoses. Which are D-2-ketopentoses, which are $\mathrm{L}-2$ -ketopentoses, and which are enantiomers? Refer to Table $20-2$ and write the name of each 2 -ketopentose.

Carbohydrates

00:52

General Chemistry: Principles and Modern Applications

For each pair of structures shown below, indicate whether the two species are identical molecules, enantiomers, or isomers of some other sort.

Structures of Organic Compounds

04:59

General Chemistry: Principles and Modern Applications

Consider the following pairs of structures. In each case, are the structures different conformers or are they isomers? If they are isomers, then state whether they are constitutional isomers, diastereomers, or enantiomers.

Structures of Organic Compounds

Chirality and R/S configuration

25 Practice Problems

01:02

Introduction to General, Organic and Biochemistry

Following is the structure of immunosuppressant FK-506, a molecule shown to disrupt calcineurinmediated signal transduction in T-lymphocytes.
(a) There are three carbon-carbon double bonds present in this molecule. Which of the three has the potential for cis/trans isomerism? Assign a cis or trans configuration to each carbon-carbon double bond that has this possibility.
(b) How many stereocenters are present in this molecule? How many stereoisomers are possible for it?
(c) Are there any aromatic components in this molecule?
(d) Consider the two carbon atoms marked with asterisks. Assign an $R$ or $S$ configuration of each stereocenter.
(e) Because of the presence of a 21 -member ring, this molecule is described as a macrocycle. This ring is fashioned by three types of bonds, several carboncarbon bonds, one ester, one hemiacetal, and one amide. Locate the ester and the hemiacetal.
(f) Draw the structural formula of the long chain compound that would result if the hemiacetal were to be cleaved to an alcohol and a carbonyl group.

Aldehydes and Ketones

08:50

Organic Chemistry

a. Will thermal 1,3-migrations of carbon occur with retention or inversion of configuration?
b. Will thermal 1,5-migrations of carbon occur with retention or inversion of configuration?

Pericyclic Reactions

02:47

Organic Chemistry

Indicate whether each of the following structures has the $R$ or the $S$ configuration:

Stereochemistry

E and Z designations for alkenes

4 Practice Problems

10:47

Organic Chemistry

a. Give the structures and the systematic names for all alkenes with molecular formula $\mathrm{C}_{6} \mathrm{H}_{12}$, ignoring cis-trans isomers. (Hint: There are 13.)
b. Which of the compounds have $E$ and $Z$ isomers?

Alkenes • Thermodynamics and Kinetics

01:21

Organic Chemistry

Dimethyldioxirane (DMDO), whose structure is shown below, is another reagent commonly used for alkene epoxidation. Write a mechanism for the epoxidation of ( $Z$ )- - -butene by DMDO, including a possible transition state structure. What is the by-product of a DMDO epoxidation?

Alcohols and Ethers

11:45

Organic Chemistry

Using the $(E)-(Z)$ designation [and in parts (e) and ( $\mathbf{f}$ ) the $(R)-(S)$ designation as well] give IUPAC names for each of the following: (FIGURE CANNOT COPY)

Alkenes and Alkynes I