Additional Problems 1

Kirsten Kramer; Cassandra Lilly

Additional Problems 1

Visualizing Chemistry

Problem 1.30
Convert each of the following molecular models into a skeletal structure, and give the formula of 1-18 each. Only the connections between atoms are shown; multiple bonds are not indicated (black = C, red = O, blue = N, gray = H).

(a)

Ball and stick model of a six-membered ring with one nitrogen in the ring, with a propyl substituent on the adjacent carbon.

(b)

Ball and stick model of a three carbon chain; C 1 is carboxyl, C 2 has an N H 2 substituent.

Problem 1.31
The following model is a representation of citric acid, the key substance in the so-called citric acid cycle, by which food molecules are metabolized in the body. Only the connections between atoms are shown; multiple bonds are not indicated. Complete the structure by indicating the positions of multiple bonds and lone-pair electrons (black = C, red = O, gray = H).

The ball and stick model of citric acid where grey, black and red spheres represent hydrogen, carbon, oxygen, respectively.

Problem 1.32
The following model is a representation of acetaminophen, a pain reliever sold in drugstores under a variety of names, including Tylenol. Identify the hybridization of each carbon atom in acetaminophen, and tell which atoms have lone pairs of electrons (black = C, red = O, blue = N, gray = H).

The ball and stick model of acetaminophen where grey, black, blue and red spheres represent hydrogen, carbon, nitrogen, and oxygen, respectively.

Problem 1.33
The following model is a representation of aspartame, C₁₄H₁₈N₂O₅, known commercially under many names, including NutraSweet. Only the connections between atoms are shown; multiple bonds are not indicated. Complete the structure for aspartame, and indicate the positions of multiple bonds (black = C, red = O, blue = N, gray = H).

The ball and stick model of aspartame where grey, black, blue and red spheres represent hydrogen, carbon, nitrogen, and oxygen, respectively.

Electron Configurations

Problem 1.34
How many valence electrons does each of the following dietary trace elements have?

(a) Zinc (b) Iodine (c) Silicon (d) Iron

Problem 1.35
Give the ground-state electron configuration for each of the following elements:

(a) Potassium (b) Arsenic (c) Aluminum (d) Germanium

Electron-Dot and Line-Bond Structures

Problem 1.36
What are likely formulas for the following molecules?

(a) NH_?OH

(b) AlCl_?

(c) CF₂Cl_?

(d) CH_?O

Problem 1.37
Why can’t molecules with the following formulas exist?

(a) CH₅

(b) C₂H₆N

(c) C₃H₅Br₂

Problem 1.38
Draw an electron-dot structure for acetonitrile, C₂H₃N, which contains a carbon–nitrogen triple bond. How many electrons does the nitrogen atom have in its outer shell? How many are bonding, and how many are nonbonding?

Problem 1.39
Draw a line-bond structure for vinyl chloride, C₂H₃Cl, the starting material from which PVC poly(vinyl chloride) plastic is made.

Problem 1.40
Fill in any nonbonding valence electrons that are missing from the following structures:

(a)

Chemical structure of C H 3 S S C H 3 showing no nonbonding pairs.

(b)

Chemical structure of C H 3 C O N H 2 showing no nonbonding pairs.

(c)

Chemical structure of C H 3 C O O with a negative on one of the oxygen atoms, showing no nonbonding pairs.

Problem 1.41
Convert the following line-bond structures into molecular formulas:

(a)

Chemical structure of a benzene ring with a carboxyl group and an acetoxy group on adjacent carbons.

(b)

Chemical structure of vitamin C.

(c)

Chemical structure of nicotine.

(d)

Chemical structure of a six-membered ring incorporating one oxygen. There are hydroxyl groups on four of the carbons and a hydroxymethyl group on the fifth.

Problem 1.42
Convert the following molecular formulas into line-bond structures that are consistent with valence rules:

(a) C₃H₈

(b) CH₅N

(c) C₂H₆O (2 possibilities)

(d) C₃H₇Br (2 possibilities)

(e) C₂H₄O (3 possibilities)

(f) C₃H₉N (4 possibilities)

Problem 1.43
Draw a three-dimensional representation of the oxygen-bearing carbon atom in ethanol, CH₃CH₂OH, using the standard convention of solid, wedged, and dashed lines.

Problem 1.44
Oxaloacetic acid, an important intermediate in food metabolism, has the formula C₄H₄O₅ and contains three C=O bonds and two O–H bonds. Propose two possible structures.

Problem 1.45
Draw structures for the following molecules, showing lone pairs:

(a) Acrylonitrile, C₃H₃N, which contains a carbon–carbon double bond and a carbon–nitrogen triple bond

(b) Ethyl methyl ether, C₃H₈O, which contains an oxygen atom bonded to two carbons

(c) Butane, C₄H₁₀, which contains a chain of four carbon atoms

(d) Cyclohexene, C₆H₁₀, which contains a ring of six carbon atoms and one carbon–carbon double bond

Hybridization

Problem 1.46
What is the hybridization of each carbon atom in acetonitrile?

Problem 1.47
What kind of hybridization do you expect for each carbon atom in the following molecules?

(a)

(b)

(c)

(d)

Text saying acetic acid and condensed structural formula of C H 3 C O O H, with a double bond between carbon and one oxygen.

Problem 1.48
What is the shape of benzene, and what hybridization do you expect for each carbon?

The line-bond structure of benzene.

Problem 1.49
What bond angle do you expect for each of the indicated atoms, and what kind of hybridization do you expect for the central atom in each molecule?

(a)

Condensed structural formula of glycine, an amino acid: H 2 N C H 2 C O O H. The carboxyl carbon and both oxygens are highlighted in red.

(b)

Condensed structural formula of pyridine, a ring of five carbons and one nitrogen with alternating single and double bonds. The nitrogen and adjacent carbons are highlighted in red.

(c)

Structure of lactic acid (in sour milk), a propionic acid with a hydroxyl group on C 2. The three carbons are highlighted in red.

Problem 1.50
Propose structures for molecules that meet the following descriptions:

(a) Contains two sp²-hybridized carbons and two sp³-hybridized carbons

(b) Contains only four carbons, all of which are sp²-hybridized

(c) Contains two sp-hybridized carbons and two sp²-hybridized carbons

Problem 1.51
What kind of hybridization do you expect for each carbon atom in the following molecules:

(a)

The line-bond structure of procaine.

(b)

The line-bond structure of vitamin C (ascorbic acid).

Problem 1.52
Pyridoxal phosphate, a close relative of vitamin B₆, is involved in a large number of metabolic reactions. What is the hybridization and the bond angle for each nonterminal atom?

The chemical structure of pyridoxal phosphate featuring a negative charge on two of the phosphate oxygen atoms.

Skeletal Structures

Problem 1.53
Convert the following structures into skeletal drawings:

(a)

Structural formula of indole, with fused five- and six-membered rings with alternating single and double bonds. There is a nitrogen with one hydrogen in the ring adjacent to the fusion.

(b)

Structural formula of 1,3-pentadiene, a five-carbon chain with alternating single and double bonds.

(c)

Structural formula of 1,2-dichlorocyclopentane, a ring of five carbon atoms with chlorines on adjacent carbons.

(d)

Structural formula of benzoquinone, a six-membered ring with carbonyl groups at C 1 and C 4 and double bonds at C 2 and C 5.

Problem 1.54
How many hydrogens are bonded to each carbon atom in the following substances, and what is the molecular formula of each?

(a)

Line-bond structure of a benzene ring with isopropyl and nitrile substituents on adjacent carbons.

(b)

Line-bond structure of benzene fused to a cyclohexane. There’s a carboxyl group two carbons from a fusion point on benzene and bromine two carbons from the same fusion on cyclohexane.

(c)

Line-bond structure of two fused cyclopentanes. One pentane has a double bond and a carbonyl group, the other has a methyl substituent.

Problem 1.55
Quetiapine, marketed as Seroquel, is a heavily prescribed antipsychotic drug used in the treatment of schizophrenia and bipolar disorder. Convert the following representation into a skeletal structure, and give the molecular formula of quetiapine.

The line-bond structure of Quetiapine (Seroquel).

Problem 1.56
How many hydrogens are bonded to each carbon atom in (a) the antiinfluenza agent oseltamivir, marketed as Tamiflu, and (b) the platelet aggregation inhibitor clopidogrel, marketed as Plavix? Give the molecular formula of each.

(a)

The line-bond structure of oseltamivir (Tamiflu).

(b)

The line-bond structure of clopidogrel (Plavix).

Mechanism Problems

Problem 1.57
Predict the product(s) of the following acid/base reactions. Draw curved arrows to show the formation and breaking of bonds.

(a)

An incomplete reaction shows tetrahydrofuran reacting with B F 3. The product is not depicted.

(b)

An incomplete reaction shows H I reacting with acetone that has two lone pairs on the oxygen. The product is not depicted.

(c)

An incomplete reaction shows acetic acid reacting with methylamine. The product is not depicted.

Problem 1.58
Use curved arrows to draw the protonated form of the following Lewis bases upon reacting with H⁺.

(a)

The bond-line structure of tetrahydrofuran has a 5-membered ring made of an oxygen atom and four carbon atoms.

(b)

The bond-line structure of N-methylacetamide.

(c)

The bond-line structure of pyridine.

(d)

The bond-line structure of benzaldehyde

Problem 1.59
Double bonds can also act like Lewis bases, sharing their electrons with Lewis acids. Use curved arrows to show how each of the following double bonds will react with HCl and draw the resulting carbocation.

(a)

A methylene group is double bonded to another methylene group.

(b)

A 4-carbon chain with a double bond between C2-C3.

(c)

The bond-line structure of a cyclohexene ring.

Electronegativity and Dipole Moments

Problem 1.60
Identify the most electronegative element in each of the following molecules:

(a) CH₂FCl

(b) FCH₂CH₂CH₂Br

(c) HOCH₂CH₂NH₂

(d) CH₃OCH₂Li

Problem 1.61
Use the electronegativity table given in Figure 2.3 to predict which bond in each of the following pairs is more polar, and indicate the direction of bond polarity for each compound.

(a) H₃C–Cl or Cl–Cl

(b) H₃C–H or H–Cl

(c) HO–CH₃ or (CH₃)₃Si–CH₃

(d) H₃C–Li or Li–OH

Formal Charges

Problem 1.62
Calculate the formal charges on the atoms shown in red.

(a)

A condensed formula reads, (C H 3) 2 O B F 3. The O atom carries a lone pair.

(b)

A methylene group with a lone pair on the carbon is single bonded to nitrogen, which is triple bonded to another nitrogen, featuring a lone pair.

(c)

A methylene group is double bonded to nitrogen, which is further double bonded to another nitrogen, featuring two lone pairs.

(d)

An oxygen atom with two lone pairs is double bonded to second oxygen that carries one lone pair and is single bonded to third oxygen, featuring three lone pairs.

(e)

A central phosphorus atom bonded to three methyl groups and a methylene group with a lone pair on the carbon.

(f)

The nitrogen atom of a pyridine ring is bonded to an oxygen atom, carrying three lone pairs.

Problem 1.63
Assign formal charges to the atoms in each of the following molecules:

(a)

A central nitrogen atom is bonded to three methyl groups and an oxygen atom, featuring three lone pairs.

(b)

A methyl group is bonded to a chain of three nitrogen atoms. The second and third nitrogen atoms have a triple bond in-between.

(c)

A methyl group is single bonded to a chain of three nitrogen atoms, connected by double bonds.

Resonance

Problem 1.64
Which of the following pairs of structures represent resonance forms?

(a)

The first structure has a benzene ring fused to cyclobutene. The second structure has a cyclohexadiene ring, in which C5 and C6 are each double bonded to a methylene group.

(b)

(c)

(d)

The first structure has a benzene ring bonded to an oxygen anion. The second structure has a cyclohexadiene ring with double bonded oxygen at C1 and negative charge at C4.

Acids and Bases

Problem 1.65
Alcohols can act either as weak acids or as weak bases, just as water can. Show the reaction of methanol, CH₃OH, with a strong acid such as HCl and with a strong base such as Na⁺ ^–NH₂

Problem 1.66
Draw electron-dot structures for the following molecules, indicating any unshared electron pairs. Which of the compounds are likely to act as Lewis acids and which as Lewis bases?

(a) AlBr₃

(b) CH₃CH₂NH₂

(c) BH₃

(d) HF

(e) CH₃SCH₃

(f) TiCl₄

Problem 1.67
Write the products of the following acid–base reactions:

(a) CH₃OH + H₂SO₄ ⇄ ?

(b) CH₃OH + NaNH₂ ⇄ ?

(c) CH₃NH₃⁺ Cl^– + NaOH ⇄ ?

Problem 1.68
Rank the following substances in order of increasing acidity:

The structures of acetone, 2,4-pentanedione, phenol, and acetic acid with their respective p K a values, 19.3, 9, 9.9, and 4.76.

Problem 1.69
Which, if any, of the substances in Problem 1.68 is a strong enough acid to react almost completely with NaOH? (The pK_a of H₂O is 15.74.)

Problem 1.70
The ammonium ion (NH₄⁺, pK_a = 9.25) has a lower pK_a than the methylammonium ion (CH₃NH₃⁺, pK_a = 10.66). Which is the stronger base, ammonia (NH₃) or methylamine (CH₃NH₂)? Explain.

Problem 1.71
Predict the structure of the product formed in the reaction of the organic base pyridine with the organic acid acetic acid, and use curved arrows to indicate the direction of electron flow.

In an incomplete reaction, pyridine reacts with acetic acid to form unknown product(s), depicted by a question mark.

Problem 1.72
Sodium bicarbonate, NaHCO₃, is the sodium salt of carbonic acid (H₂CO₃), pK_a = 6.37. Which of the substances shown in Problem 1.68 will react significantly with sodium bicarbonate?

General Problems

Problem 1.73
Why do you suppose no one has ever been able to make cyclopentyne as a stable molecule?

The skeletal structure of cyclopentyne featuring a triple bond within a five-carbon ring.

Problem 1.74
Allene, H₂C=C=CH₂, has two adjacent double bonds. Draw a picture showing the orbitals involved in the σ and π bonds of allene. Is the central carbon atom sp²– or sp-hybridized? What about the hybridization of the terminal carbons? What shape do you predict for allene?

Problem 1.75
Allene (see Problem 1-74) is structurally related to carbon dioxide, CO₂. Draw a picture showing the orbitals involved in the σ and π bonds of CO₂, and identify the likely hybridization of carbon.

Problem 1.76
Complete the electron-dot structure of caffeine, showing all lone-pair electrons, and identify the hybridization of the indicated atoms.

The line-bond structure of caffeine featuring three arrows and red text highlighting C2, C8, and N9 atoms.

Problem 1.77
Most stable organic species have tetravalent carbon atoms, but species with trivalent carbon atoms also exist. Carbocations are one such class of compounds.

A chemical structure of a carbocation featuring a carbon atom with a positive charge bonded to three hydrogen atoms.

(a) How many valence electrons does the positively charged carbon atom have?

(b) What hybridization do you expect this carbon atom to have?

(c) What geometry is the carbocation likely to have?

Problem 1.78
A carbanion is a species that contains a negatively charged, trivalent carbon.

A chemical structure of a carbanion featuring a carbon atom with a negative charge and a lone pair bonded to three hydrogen atoms.

(a) What is the electronic relationship between a carbanion and a trivalent nitrogen compound such as NH₃?

(b) How many valence electrons does the negatively charged carbon atom have?

(c) What hybridization do you expect this carbon atom to have?

(d) What geometry is the carbanion likely to have?

Problem 1.79
Two different substances have the formula C₄H₁₀. Draw both, and tell how they differ.

Problem 1.80
Two different substances have the formula C₃H₆. Draw both, and tell how they differ.

Problem 1.81
Two different substances have the formula C₂H₆O. Draw both, and tell how they differ.

Problem 1.82
Three different substances contain a carbon–carbon double bond and have the formula C₄H₈. Draw them, and tell how they differ.

Problem 1.83
Among the most common over-the-counter drugs you might find in a medicine cabinet are mild pain relievers such ibuprofen (Advil, Motrin), naproxen (Aleve), and acetaminophen (Tylenol).

The skeletal structures of ibuprofen, naproxen, and acetaminophen.

(a) How many sp³-hybridized carbons does each molecule have?

(b) How many sp²-hybridized carbons does each molecule have?

(c) What similarities can you see in their structures?

Problem 1.84
Identify the acids and bases in the following reactions:

(a)

In a reaction, acetone reacts with T i C l 4 to form a product (the oxygen is positively charged and is bonded to T i C l 4 negative).

(b)

In a reaction, morpholine reacts with B H 3 to form a product with a positive charge and single bonded B H 3 negative at the nitrogen of the ring.

Problem 1.85
Which of the following pairs represent resonance structures?

Two Lewis structures of protonated benzamide; one is protonated at the N, the other at the O.

Problem 1.86
Phenol, C₆H₅OH, is a stronger acid than methanol, CH₃OH, even though both contain an O–H bond. Draw the structures of the anions resulting from loss of H⁺ from phenol and methanol, and use resonance structures to explain the difference in acidity.

The structures of phenol and methanol with their respective p K a values, 9.89 and 15.54.

Problem 1.87
Thiamin diphosphate (TPP), a derivative of vitamin B₁ required for glucose metabolism, is a weak acid that can be deprotonated by a base. Assign formal charges to the appropriate atoms in both TPP and its deprotonation product.

Thiamin diphosphate reacts with base forming a product, in which the hydrogen (with p K a 18) at C2 of the 5-membered ring is replaced with a lone pair.

Problem 1.88
Use the pK_a table in Appendix B to determine in which direction the equilibrium is favored.

(a)

In a reversible reaction, phenol reacts with benzene bonded to carboxylate ion to form phenoxide ion and benzoic acid.

(b)

In a reversible reaction, propanol reacts with a negatively charged amine to form a 3-carbon chain bonded to an oxygen ion and ammonia.

(c)

In a reversible reaction, a methyl ion reacts with nitromethane to form methane and a methylene group with a negative charge bonded to a nitro group.

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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.