Additional Problems 2

Kirsten Kramer; Cassandra Lilly

Additional Problems 2

Visualizing Chemistry

Problem 2.32
Identify the functional groups in the following substances, and convert each drawing into a molecular formula (red = O, blue = N).

(a)

A ball and stick model of phenylalanine that includes a benzene ring.

(b)

A ball and stick model of lidocaine that includes an amide group.

Problem 2.33
Give IUPAC names for the following alkanes, and convert each drawing into a skeletal structure.

(a)

A ball and stick model of 3,3,5-trimethylheptane

(b)

A ball and stick model of 2-methyl-3-ethylpentane

(c)

A ball and stick model of 2,4,4-trimethylpentane

(d)

A ball and stick model of 2-methyl-4-isopropylheptane

Problem 2.34
Draw a Newman projection along the C2–C3 bond of the following conformation of 2-butanol.

A ball and stick model of 2-butanol is represented. The grey, white and red spheres are carbon, white, and oxygen.

Problem 2.35
Name the following cycloalkanes:

(a)

The ball and stick model of cyclopentane. C1 is bonded to an equatorial ethyl group. C3 is bonded to an equatorial methyl group. Black and gray spheres represent carbon and hydrogen, respectively.

(b)

The ball and stick model of cyclohexane. C1 is bonded to two methyl groups. C3 is bonded to an equilarial methyl group. Black and gray spheres represent carbon and hydrogen, respectively.

Problem 2.36
A trisubstituted cyclohexane with three substituents—red, green, and blue—undergoes a ring-flip to its alternate chair conformation. Identify each substituent as axial or equatorial, and show the positions occupied by the three substituents in the ring-flipped form.

Ball and stick model of substituted cyclohexane with red, blue, and green spheres at C1, C2, and C5 undergoes ring-flip to form model with all substituents, represented by white circles.

Problem 2.37
The following cyclohexane derivative has three substituents—red, green, and blue. Identify each substituent as axial or equatorial, and identify each pair of relationships (red–blue, red–green, and blue–green) as cis or trans.

The ball and stick model of cyclohexane. C1 is axially bonded to a green sphere. C2 and C5 are equatorially bonded to a blue sphere and a red sphere, respectively.

Problem 2.38
Glucose exists in two forms having a 36:64 ratio at equilibrium. Draw a skeletal structure of each, describe the difference between them, and tell which of the two you think is more stable (red = O).

The ball and stick models of alpha-glucose and beta-glucose. In alpha-glucose, C1 is bonded to an axial hydroxyl group (below the ring). In beta-glucose, C1 is bonded to an equatorial hydroxyl group (above the ring).

Functional Groups

Problem 2.39
Locate and identify the functional groups in the following molecules.

(a)

A benzene ring with C H 2 O H group on the C 1 and N H C H 3 group on the C 2 carbon is represented.

(b)

A six membered ring with a double bond and a carbonyl group is represented.

(c)

A benzene ring linked to an N H group linked to a C O C H 3 group is represented.

(d)

A C H 3 group linked to a C H connected to an amine group is shown. The C H is connected to a C O O H group.

(e)

Two six membered rings fused together is shown. Both the rings have double bond, carbonyl group and a C H 3 group.

(f)

Two C H 3 groups linked to a triple bond linked to a carbonyl linked to a chlorine group.

Problem 2.40
Propose structures that meet the following descriptions:

(a) A ketone with five carbons

(b) A four-carbon amide

(c) A five-carbon ester

(d) An aromatic aldehyde

(e) A keto ester

(f) An amino alcohol

Problem 2.41
Propose structures for the following:

(a) A ketone, C₄H₈O

(b) A nitrile, C₅H₉N

(c) A dialdehyde, C₄H₆O₂

(d) A bromoalkene, C₆H₁₁Br

(e) An alkane, C₆H₁₄

(f) cyclic saturated hydrocarbon, C₆H₁₂

(g) A diene (dialkene), C₅H₈

(h) A keto alkene, C₅H₈O

Problem 2.42
Predict the hybridization of the carbon atom in each of the following functional groups:

(a) Ketone

(b) Nitrile

(c) Carboxylic acid

Problem 2.43
Draw the structures of the following molecules:

(a) Biacetyl, C₄H₆O₂, a substance with the aroma of butter; it contains no rings or carbon– carbon multiple bonds.

(b) Ethylenimine, C₂H₅N, a substance used in the synthesis of melamine polymers; it contains no multiple bonds.

(c) Glycerol, C₃H₈O₃, a substance isolated from fat and used in cosmetics; it has an –OH group on each carbon.

Isomers

Problem 2.44
Draw structures that meet the following descriptions (there are many possibilities):

(a) Three isomers with the formula C₈H₁₈

(b) Two isomers with the formula C₄H₈O₂

Problem 2.45
Draw structures of the nine isomers of C₇H₁₆.

Problem 2.46
In each of the following sets, which structures represent the same compound and which represent different compounds?

(a)

Three structures with alkane groups are represented. The structure that represent the same compound and different compounds have to be identified.

(b)

Three benzene rings with two O H group as substituents at different rings is shown.

(c)

Three compounds having a six membered ring is represented. There are O H groups as the substituent in these compounds.

Problem 2.47
Seven constitutional isomers have the formula C₄H₁₀O. Draw as many as you can.

Problem 2.48
Draw as many compounds as you can that fit the following descriptions:

(a) Alcohols with formula C₄H₁₀O

(b) Amines with formula C₅H₁₃N

(c) Ketones with formula C₅H₁₀O

(d) Aldehydes with formula C₅H₁₀O

(e) Esters with formula C₄H₈O₂

(f) Ethers with formula C₄H₁₀O

Problem 2.49
Draw compounds that contain the following:

(a) A primary alcohol

(b) A tertiary nitrile

(c) A secondary thiol

(d) Both primary and secondary alcohols

(e) An isopropyl group

(f) A quaternary carbon

Cycloalkane Isomers

Problem 2.50
Draw the five cycloalkanes with the formula C₅H₁₀.

Problem 2.51
Give IUPAC names for the following compounds.

(a)

In a 7-membered ring, C1 is bonded to a methyl group.

(b)

In a cyclopentane ring, C1 and C3 are each wedge bonded to methyl groups and dash bonded to hydrogen atoms.

(c)

In a cyclohexane ring, C1 is dash bonded to methyl and wedge bonded to hydrogen atom. C2 is wedge bonded to methyl and dash bonded to hydrogen.

(d)

In a cyclobutane ring, C1 is wedge bonded to an isopropyl group. C2 is dash bonded to a methyl group.

(e)

In a cyclohexane ring, C1 is bonded to two methyl groups. C4 is bonded to a single methyl group.

Problem 2.52
Draw a stereoisomer of trans-1,3-dimethylcyclobutane.

Problem 2.53
Tell whether the following pairs of compounds are identical, constitutional isomers, stereoisomers, or unrelated.

(a) cis-1,3-Dibromocyclohexane and trans-1,4-dibromocyclohexane

(b) 2,3-Dimethylhexane and 2,3,3-trimethylpentane

(c)

Two structures of cyclopentane each with chlorine atoms at first and third carbons. The relative position of the chlorine atoms are cis in both structures.

Problem 2.54
Draw three isomers of trans-1,2-dichlorocyclobutane, and label them as either constitutional isomers or stereoisomers.

Problem 2.55
Identify each pair of relationships among the –OH groups in glucose (red–blue, red–green, red–black, blue–green, blue–black, green–black) as cis or trans.

The Haworth projection of glucose has a pyranose ring with its four carbons bonded to hydroxyl groups and one carbon is bonded to a hydroxymethyl group.

Naming Compounds

Problem 2.56
Draw and name all monobromo derivatives of pentane, C₅H₁₁Br.

Problem 2.57
Draw and name all monochloro derivatives of 2,5-dimethylhexane, C₈H₁₇Cl.

Problem 2.58
Draw structures for the following:

(a) 2-Methylheptane

(b) 4-Ethyl-2,2-dimethylhexane

(c) 4-Ethyl-3,4-dimethyloctane

(d) 2,4,4-Trimethylheptane

(e) 3,3-Diethyl-2,5-dimethylnonane

(f) 4-Isopropyl-3-methylheptane

Problem 2.59
Draw a compound that:

(a) Has only primary and tertiary carbons

(b) Has no secondary or tertiary carbons

(c) Has no secondary or tertiary carbons

Problem 2.60
Draw a compound that:

(a) Has nine primary hydrogens

(b) Has only primary hydrogens

Problem 2.61
Give IUPAC names for the following compounds:

(a)

The compound is a five membered ring with a C H 3 group on the second position.

(b)

The given compound is a four membered ring. Two C H 3 groups are present on the third position.

(c)

The given compound is a six membered ring. A C H 3 group is present on C 2 and two C H 3 groups are present on C3.

(d)

The given compound is a seven membered ring with a C H 2 C H 3 on the third position and C H 3 on the sixth position.

(e)

The compound comprises seven carbon with a C H 3 on the C4 carbon and a C H 3 and C H 2 C H 3 on the C6 carbon.

(f)

A six membered ring with two C H 3 groups on C 2 carbon and two C H 3 groups on the C 3 carbon is shown.

Problem 2.62
Name the five isomers of C₆H₁₄.

Problem 2.63
Explain why each of the following names is incorrect:

(a) 2,2-Dimethyl-6-ethylheptane

(b) 4-Ethyl-5,5-dimethylpentane

(c) 3-Ethyl-4,4-dimethylhexane

(d) 5,5,6-Trimethyloctane

(e) 2-Isopropyl-4-methylheptane

Problem 2.64
Propose structures and give IUPAC names for the following:

(a) A diethyldimethylhexane

(b) A (3-methylbutyl)-substituted alkane

Conformations

Problem 2.65
Consider 2-methylbutane (isopentane). Sighting along the C2–C3 bond:

(a) Draw a Newman projection of the most stable conformation.

(b) Draw a Newman projection of the least stable conformation.

Problem 2.66
Draw the most stable conformation of pentane, using wedges and dashes to represent bonds coming out of the paper and going behind the paper, respectively.

Problem 2.67
Draw the most stable conformation of 1,4-dichlorobutane, using wedges and dashes to represent bonds coming out of the paper and going behind the paper, respectively.

General Problems

Problem 2.68
For each of the following compounds, draw an isomer that has the same functional groups.

(a)

A four membered ring with C H 3 on the C2 and Br group is represented.

(b)

A five membered ring with an O C H 3 group is represented.

(c)

A four membered carbon chain with a cyano group is represented.

(d)

A six membered ring with an O H group is represented.

(e)

A three membered ring with a C H O group is represented.

(f)

A benzene ring with a C H 2 C O O H group is represented.

Problem 2.69
Malic acid, C₄H₆O₅, has been isolated from apples. Because this compound reacts with 2 molar equivalents of base, it is a dicarboxylic acid.

(a) Draw at least five possible structures.

(b) If malic acid is a secondary alcohol, what is its structure?

Problem 2.70
Increased substitution around a bond leads to increased strain. Take the four substituted butanes listed below, for example. For each compound, sight along the C2–C3 bond and draw Newman projections of the most stable and least stable conformations.

(a) 2-Methylbutane

(b) 2,2-Dimethylbutane

(c) 2,3-Dimethylbutane

(d) 2,2,3-Trimethylbutane

Problem 2.71
The cholesterol-lowering agents called statins, such as simvastatin (Zocor) and pravastatin (Pravachol), are among the most widely prescribed drugs in the world, with annual sales estimated at approximately $25 billion. Identify the functional groups in both, and tell how the two substances differ.

The chemical structures of simvastatin and pravastatin are represented.

Problem 2.72
There are two isomeric substances, both named 1,2-dimethylcyclohexane. Explain.

The chemical structure of 1,2-dimethylcyclohexane is represented.

Problem 2.73
The statin drugs, such as simvastatin (Zocor), pravastatin (Pravachol), and atorvastatin (Lipitor) are the most widely prescribed drugs in the world.

The structures of simvastatin (Zocor), pravastatin (Pravachol), and atorvastatin (Lipitor).

(a) Are the two indicated bonds on simvastatin cis or trans?

(b) What are the cis/trans relationships among the three indicated bonds on pravastatin?

(c) Why can’t the three indicated bonds on atorvastatin be identified as cis or trans?

Problem 2.74
Tell whether each of the following substituents on a steroid is axial or equatorial. A substituent that is “up” is on the top side of the molecule as drawn, and a substituent that is “down” is on the bottom side.

(a) Substituent up at C3

(b) Substituent down at C7

(c) Substituent down at C11

Chair conformation of the steroid ring system with three cyclohexane rings fused together and one cyclopentane ring. Hydrogen atom and methyl groups are bonded to the top face of the ring junctions.

Cycloalkane Conformation and Stability

Problem 2.75
A 1,2-cis disubstituted cyclohexane, such as cis-1,2-dichlorocyclohexane, must have one group axial and one group equatorial. Explain.

Problem 2.76
A 1,2-trans disubstituted cyclohexane must have either both groups axial or both groups equatorial. Explain.

Problem 2.77
Assume that you have a variety of cyclohexanes substituted in the positions indicated. Identify the substituents as either axial or equatorial. For example, a 1,2-cis relationship means that one substituent must be axial and one equatorial, whereas a 1,2-trans relationship means that both substituents are axial or both are equatorial.

(a) 1,3-Trans disubstituted

(b) 1,4-Cis disubstituted

(c) 1,3-Cis disubstituted

(d) 1,5-Trans disubstituted

(e) 1,5-Cis disubstituted

(f) 1,6-Trans disubstituted

Cyclohexane Conformational Analysis

Problem 2.78
Draw the two chair conformations of trans-1-chloro-2-methylcyclohexane. Which is more stable?

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