Additional Problems 4

Visualizing Chemistry

Problem 4.22
Name the following alkenes, and convert each drawing into a skeletal structure:

(a)

The ball-and-stick model has a 6-carbon chain. C2 is double bonded to C3. C2, C4, and C5 are each bonded to a methyl group.

(b)

The ball-and-stick model has a cyclohexene ring. C1 is bonded to an ethyl group. C3 is bonded to two methyl groups.

Problem 4.23
Assign E or Z stereochemistry to the double bonds in each of the following alkenes, and convert each drawing into a skeletal structure (red = O, green = Cl):

(a)

The ball-and-stick model has a 2-carbon chain with double bond. C1 is bonded to chlorine and methyl. C2 is bonded to an aldehyde and an isopropyl group.

(b)

The ball-and-stick model has 5-carbon chain with alternate double bonds. C2 and C3 are each bonded to methyl. C4 is bonded to methoxy. C5 is carboxylic acid.

Problem 4.24
The following alkyl halide can be prepared by addition of HBr to two different alkenes. Draw the structures of both (reddish-brown = Br).

The ball-and-stick model has a 5-carbon chain. C2 is bonded to a bromine atom. The gray, white, and reddish-brown spheres represent carbon, hydrogen, and bromine, respectively.

Problem 4.25
The following structure represents the carbocation intermediate formed in the addition reaction of HBr to two different alkenes. Draw the structures of both.

The ball-and-stick model has a cyclohexane ring in its chair conformation. C1 is bonded to a methyl group.

Problem 4.26
Electrostatic potential maps of (a) formaldehyde (CH2O) and (b) methanethiol (CH3SH) are shown. Is the formaldehyde carbon atom likely to be electrophilic or nucleophilic? What about the methanethiol sulfur atom? Explain.

(a)

The electrostatic potential map of formaldehyde. The gray, white, and red spheres at the center represent carbon, hydrogen, and oxygen atoms, respectively.

(b)The electrostatic potential map of methanethiol shows a ball-and-stick model in the center, in which gray, white, and yellow spheres represent carbon, hydrogen, and sulfur atoms, respectively.

Problem 4.27
Look at the following energy diagram:

An energy diagram shows a curve forming two crests and one trough. The second crest is higher than the first, and the endpoint is higher than the start.

(a) Is ΔG° for the reaction positive or negative? Label it on the diagram.

(b) How many steps are involved in the reaction?

(c) How many transition states are there? Label them on the diagram.

Problem 4.28
Look at the following energy diagram for an enzyme-catalyzed reaction:

An energy diagram shows a curve forming four crests of varying height. The endpoint is lower than the start.

(a) How many steps are involved?

(b) Which step is most exergonic?

(c) Which step is slowest?

Naming Alkenes

Problem 4.29
Name the following alkenes:

(a)

A double bond with hydrogen (up) and methyl (down) substituents on the left and s-butyl (up) and hydrogen (down) substituents on the right.

(b)

A double bond with 2-methylheptane connected by C 5 (up) and methyl (down) substituents on the left and methyl (up) and hydrogen (down) substituents on the right.

(c)

A double bond withtwo hydrogen substituents on the left and two ethyl substituents on the right.  

(d)

A double bond with H (up) and 3-methyl-1-pentene connected by C 4 (down) substituents on the left and methyl (up) and hydrogen (down) substituents on the right.

(e) 

An 8-carbon chain with double bonds between C2-C3 and C4-C5. C4 and C5 are each bonded to a methyl group (opposite sides). 

(f)  The structure has a methylene group double bonded to carbon, which is double bonded to C H C H 3.

Problem 4.30
Draw structures corresponding to the following systematic names:

(a) (4E)-2,4-Dimethyl-1,4-hexadiene

(b) cis-3,3-Dimethyl-4-propyl-1,5-octadiene

(c) 4-Methyl-1,2-pentadiene

(d) (3E,5Z)-2,6-Dimethyl-1,3,5,7-octatetraene

(e) 3-Butyl-2-heptene

(f) trans-2,2,5,5-Tetramethyl-3-hexene

Problem 4.31
Name the following cycloalkenes:

(a)

A six-membered ring with one double bond. There is a methyl group one carbon from the double bond.

(b)

A five-membered ring with one double bond. There are methyl groups on a double-bonded carbon and on the single-bonded carbon next to it.

(c)

A four-membered ring with two double bonds. There is one ethyl substituent.

(d)

A six-membered ring with two double bonds opposite one another on the ring. There are methyl groups at each end of one double bond.

(e)

A six-membered ring with two double bonds separated by one single bond. There is one methyl group one carbon away from the end of one double bond.

(f)

An eight-membered ring with two double bonds opposite one another on the ring.

Problem 4.32
Ocimene is a triene found in the essential oils of many plants. What is its IUPAC name, including stereochemistry?

An eight-carbon chain with bonds (from left) as: single, double, single, single, double, single, double. There are methyl groups at the second and sixth carbons from the left.

Problem 4.33
α-Farnesene is a constituent of the natural wax found on apples. What is its IUPAC name, including stereochemistry?

Twelve-carbon chain with bonds (from left) as: single, double, single, single, single, double, single, single, double, single, double. Methyl groups at the second, sixth, and tenth carbons from the left.

Problem 4.34
Menthene, a hydrocarbon found in mint plants, has the systematic name 1-isopropyl-4- methylcyclohexene. Draw its structure.

Problem 4.35
Draw and name the six alkene isomers, C5H10, including E,Z isomers.

Naming Alkynes

Problem 4.36
Give IUPAC names for the following compounds:

(a)

A C8 internal alkyne with two methyl groups at C2 and a triple bond at C3.

(b)

A C8 dialkyne with triple bonds at C2 and C5 positions.

(c)

A C9 enyne with a triple bond at C3, double bond at C5 , and two methyl groups at C2 and C5.

(d)

A C8 dialkyne with triple bonds at C1 , C5, and two methyl groups at C4.

(e)

A C6 dienyne with a triple bond at C2 and two double bonds at C3 and C5.

(f)

A C13 alkyne with a methyl group at C2, a triple bond at C4, and two ethyl groups at C3 and C6.

Problem 4.37
Draw structures corresponding to the following names:

(a) 3,3-Dimethyl-4-octyne

(b) 3-Ethyl-5-methyl-1,6,8-decatriyne

(c) 2,2,5,5-Tetramethyl-3-hexyne

(d) 3,4-Dimethylcyclodecyne

(e) 3,5-Heptadien-1-yne

(f) 3-Chloro-4,4-dimethyl-1-nonen-6-yne

(g) 3-sec–Butyl-1-heptyne

(h) 5-tert-Butyl-2-methyl-3-octyne

Problem 4.38
The following two hydrocarbons have been isolated from various plants in the sunflower family. Name them according to IUPAC rules.

(a) CH3CH=CHC≡CC≡CCH=CHCH=CHCH=CH2 (all trans)

(b) CH3C≡CC≡CC≡CC≡CC≡CCH=CH2

Alkene Isomers and Their Stability

Problem 4.39
Rank the following sets of substituents according to the Cahn–Ingold–Prelog sequence rules:

(a) The figure shows four sets of substituents. Methyl, bromine, hydrogen, and iodine each with an open single bond.

(b) The figure shows four sets of substituents. A hydroxyl group, methoxy group, hydrogen atom, and carboxylic acid group each with an open single bond.

(c) The figure shows four sets of substituents. Carboxyl, methyl ester, hydroxymethyl, and methyl each with an open single bond.

(d) The figure shows three sets of substituents. Methyl, ethyl, C H 2 C H 2 O H, and acetyl group bonded to methyl each with an open single bond.

(e) The figure shows four sets of substituents. Vinyl, cyano, C H 2 N H 2, and bromomethyl each with an open single bond.

(f) The figure shows four sets of substituents. Vinyl, ethyl, C H 2 O C H 3, and hydroxymethyl with open single bonds.

Problem 4.40
Assign E or Z configuration to each of the following compounds:

(a)

A double bond with hydroxymethyl (up) and methyl (down) substituents on the left and methyl (up) and hydrogen (down) substituents on the right.

(b)

A double bond with carbonyl (up) and chlorine (down) substituents on the left and hydrogen (up) and methoxy (down) substituents on the right.

(c)

A double bond with nitrile (up) and ethyl (down) substituents on the left and methyl (up) and hydroxymethyl (down) substituents on the right.

(d)

A double bond with methyl ester (up) and carboxyl (down) substituents on the left and vinyl (up) and ethyl (down) substituents on the right.

Problem 4.41
Which of the following E,Z designations are correct, and which are incorrect?

(a)

The structure labeled Z shows C1 of a cyclohexane ring double bonded to carbon, which is bonded to a carboxylic acid group (up). C3 (up) is bonded to a methyl group.

(b)

The structure labeled E has a double bond with hydrogen (up) and methyl (down) substituents on the left and allyl (up) and s-butyl (down) substituents on the right.

(c)

Structure labeled Z has double bond. C1 has bromine (up). C2 has C H 2 N H 2 (up) and C H 2 N H C H 3.

(d)

Structure labeled E has double bond. C1 has nitrile (up) and C H 2 N (C H 3) 2. C2 has methyl (up) and ethyl.

(e)

The structure labeled Z shows C1 of cyclopentane double bonded to carbon, which is single bonded to bromine and hydrogen atom.

(f)

Structure labeled E has double bond. C1 has hydroxymethyl (up) and C H 2 O C H 3. C2 has carboxyl (up) and acetyl.

Problem 4.42
Tamoxifen, a drug used in the treatment of breast cancer, and clomiphene, a drug used in fertility treatment, have similar structures but very different effects. Assign E or Z configuration to the double bonds in both compounds.

The structures of Tamoxifen (anticancer) and Clomiphene (fertility treatment).

Energy Diagrams and Reaction Mechanisms

Problem 4.43
What is the difference between a transition state and an intermediate?

Problem 4.44
Draw the complete mechanism for each of the following polar reactions.

(a)

2-methylbut-1-ene reacts with hydrogen chloride to form 2-chloro-2-methylbutane.

(b)

Styrene reacts with hydrogen bromide to form 1-bromoethylbenzene.

(c)

2-methylbut-2-ene reacts with hydrogen chloride to form 2-chloro-2-methylbutane.

Polar Reactions

Problem 4.45
Identify the functional groups in the following molecules, and show the polarity of each:

(a) A chemical structure of propionitrile.

(b)

A chemical structure of methoxycyclopentane.

(c)

A methyl ester with a four-carbon alkyl chain. There is a ketone group at C3.

(d)

The structure has a cyclohexadiene ring with double bonds at C2 and C5, and carbonyls at C1 and C4.

(e)

A chemical structure of 2E-but-2-enamide.

(f)

A chemical structure of benzaldehyde.

Problem 4.46
Identify the following reactions as additions, eliminations, substitutions, or rearrangements:

(a) Ethyl bromide reacts with sodium cyanide to form ethyl cyanide and sodium bromide.

(b)

A chemical structure of methamphetamine, N-methyl-1-phenylpropan-2-amine.

(c)

Cyclopentadiene reacts with a but-3-en-2-one in the presence of heat to form a ketone with a methyl group and a bridged cyclic group.

(d)

Cyclohexane reacts with nitro group bonded to another nitro group in the presence of light to form nitrocyclohexane and nitrous acid.

Problem 4.47
Identify the likely electrophilic and nucleophilic sites in each of the following molecules:

(a)

The wedge-dash structure of testosterone.

(b)

The wedge-dash structure of methamphetamine.

Problem 4.48
Identify the electrophile and the nucleophile.

(a)

The figure shows azide anion reacts with chloromethane to form C H 3 N 3 and chloride.

(b)

Benzene reacts with nitronium cation to form nitrocyclohexa-2,4-diene with a cation on C 6.

(c)

Cyclohexanone reacts with methanide anion to form 1-methylcyclohexanoxide.

Problem 4.49
Follow the flow of electrons indicated by the curved arrows in each of the following polar reactions, and predict the products that result:

(a)

2-methoxypropan-2-ol undergoes a reversible reaction with hydroxide to produce unknown product(s), depicted by a question mark. Arrows indicate hydroxide abstracts alcohol hydrogen, and methoxide leaves.

(b)

Acetone undergoes a reversible reaction with hydroxide to produce unknown product(s), depicted by a question mark. Arrows indicate hydroxide abstracts alpha hydrogen, pushing electrons toward carbonyl oxygen.

(c)

Protonated acetone undergoes a reversible reaction with water to produce unknown product(s), depicted by a question mark. Arrows indicate water attacks carbonyl, pushing electrons toward carbonyl oxygen.

(d)

1-bromo-1,2-dimethylcyclohexane undergoes a reversible reaction with methoxide to produce unknown product(s), depicted by a question mark. Arrows indicate methoxide abstracts C2 hydrogen, bromine leaves.

Problem 4.50
Show the structure of the carbocation that would result when each of the following alkenes reacts with an acid, H+.

(a)

A chemical structure of trans-2-butene.

(b)

A chemical structure of cyclopentene.

(c)

A chemical structure of 2,3-dimethylbut-2-ene.

 

General Problems

Problem 4.51
Fucoserratene and ectocarpene are sex pheromones produced by marine brown algae. What are their systematic names? (Ectocarpene is difficult; make your best guess, and then check your answer in the Student Solutions Manual.)

The structures of fucoserratene and ectocarpene.

Problem 4.52
Draw an energy diagram for the addition of HBr to 1-pentene. Let one curve on your diagram show the formation of 1-bromopentane product and another curve on the same diagram show the formation of 2-bromopentane product. Label the positions for all reactants, intermediates, and products. Which curve has the higher-energy carbocation intermediate? Which curve has the higher-energy first transition state?

License

Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

Fundamentals of Organic Chemistry Copyright © by Kirsten Kramer and Cassandra Lilly is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

Share This Book