Organic Chemistry

Marc Loudon, Jim Parise

Chapter 1

Chemical Bonding and Chemical Structure - all with Video Answers

Educators

Chapter Questions

Problem 1

How many valence electrons are found in each of the following species?
(a) $\mathrm{Na}$
(b) $\underline{C a}$
(c) $\mathrm{O}^{2-}$
(d) $\underline{B r}^{+}$

Jennifer Hudspeth

Jennifer Hudspeth

Numerade Educator

Problem 2

When two different species have the same number of electrons, they are said to be isoelectronic. Name the species that satisfies each of the following criteria:
(a) the singly charged negative ion isoelectronic with neon
(b) the singly charged positive ion isoelectronic with neon
(c) the dipositive ion isoelectronic with argon
(d) the neon species that is isoelectronic with neutral fluorine

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 3

Draw a Lewis structure for each of the following species. Show all unshared pairs and the formal charges, if any. Assume that bonding follows the octet rule in all cases.
(a) $\mathrm{HCCl}_{3}$
(b) $\mathrm{NH}_{3}$
(c) $\quad\left[\mathrm{NH}_{4}\right]^{+}$
(d) $\left[\mathrm{H}_{3} \mathrm{O}\right]^{+}$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 4

Write two reasonable Lewis structures corresponding to the formula $\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O} .$ Assume that all bonding adheres to the octet rule, and that no atom bears a formal charge.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 5

Compute the formal charges on each atom of the following structures. In each case, what is the charge on the entire structure?

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 6

Analyze the polarity of each bond in the following organic compound. Which bond, other than the $\mathrm{C}-\mathrm{C}$ bond, is the least polar one in the molecule? Which carbon has the most partial positive character?

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 7

For which of the following ions does the formal charge give a fairly accurate picture of where the charge really is? Explain in each case.
(a) $\mathrm{NH}_{4}^{+}$
(b) : $\overline{\mathrm{NH}}_{2}$
(c) ${\mathrm{C}} \mathrm{H}_{3}$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 8

Using models if necessary, draw at least two other line-and-wedge structures of dichloromethane (p. 16).

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 9

Predict the approximate geometry in each of the following molecules.
(a) $\left[\mathrm{BF}_{4}\right]^{-}$
(b) water
(c) $\mathrm{H}_{2} \mathrm{C}=\ddot{\mathrm{O}}$
(d) $\mathrm{H}_{3} \mathrm{C}-\mathrm{C}=\mathrm{N}$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 10

Estimate each of the bond angles and order the bond lengths (smallest first) in the following molecule.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 11

Which of the following ions require(s) dihedral angles to specify its structure completely? Explain.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 12

The compound benzene has only one type of carbon-carbon bond, and this bond has a length intermediate between that of a single bond and a double bond. Draw a resonance structure of benzene that, taken with the following structure, accounts for the carbon-carbon bond length.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 13

(a) Draw a resonance structure for the allyl anion that shows, along with the following structure, that the two $\mathrm{CH}_{2}$ carbons are equivalent and indistinguishable.
$$
\left[\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}-\ddot{\mathrm{C}} \mathrm{H}_{2} \leadsto\right]
$$
(b) According to the resonance structures, how much negative charge is on each of the $\mathrm{CH}_{2}$ carbons?
(c) Draw a single hybrid structure for the allyl anion that shows shared bonds as dashed lines and charges as partial charges.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 14

Sketch a plot of the wavefunction $\psi=\sin n x$ for the domain $0 \leq x \leq \pi$ for $n=1,2,$ and $3 .$ What is the relationship between the "quantum number" $n$ and the number of nodes in the wavefunction?

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 15

Use the trends in orbital shapes you've just learned to describe the general features of
(a) a $3 s$ orbital
(b) a $4 s$ orbital

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 16

Give the electronic configurations of each of the following atoms and ions. Identify the valence electrons and valence orbitals in each.
(a) oxygen atom
(b) chloride ion, $\mathrm{Cl}^{-}$
(c) potassium ion, $\mathrm{K}^{+}$
(d) sodium atom

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 17

Draw an orbital interaction diagram corresponding to Fig. 1.14 for each of the following species. Indicate which are likely to exist as diatomic species, and which would dissociate into monatomic fragments. Explain.
(a) the $\mathrm{He}_{2}^{+}$ ion
(b) the $\mathrm{H}_{2}^{-}$ ion
(c) the $\mathrm{H}_{2}^{2-}$ ion
(d) the $\mathrm{H}_{2}^{+}$ ion

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 18

The bond dissociation energy of $\mathrm{H}_{2}$ is $435 \mathrm{~kJ} \mathrm{~mol}^{-1}$ ( $104 \mathrm{kcal} \mathrm{mol}^{-1}$ ); that is, it takes this amount of energy to dissociate $\mathrm{H}_{2}$ into its atoms. Estimate the bond dissociation energy of $\mathrm{H}_{2}^{+}$ and explain your answer.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 19

Referring to your solution to Problem 1.17d, calculate the bond order of the covalent bond in the $\mathrm{H}_{2}^{+}$ ion. How does this result bear on the answer to Problem $1.18 ?$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 20

(a) Construct a hybrid orbital picture for the water molecule using oxygen $s p^{3}$ hybrid orbitals.
(b) Predict any departures from tetrahedral geometry that you might expect from the presence of two unshared electron pairs. Explain your answer.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 21

In each of the following sets, specify the one compound that is likely to have completely ionic bonds in its solid state.
$\begin{array}{llll}\text { (a) } \mathrm{CCl}_{4} & \mathrm{HCl} & \mathrm{NaAt} & \mathrm{K}_{2}\end{array}$
(b) $\mathrm{CS}_{2}$
$\begin{array}{llll}\mathrm{CsF} & \mathrm{HF} & \mathrm{XeF}_{2} & \mathrm{BF}_{3}\end{array}$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 22

In each of the following sets, specify the one compound that is likely to have completely ionic bonds in its solid state.
$\begin{array}{llll}\text { (a) } \mathrm{CCl}_{4} & \mathrm{HCl} & \mathrm{NaAt} & \mathrm{K}_{2}\end{array}$
(b) $\mathrm{CS}_{2}$
$\begin{array}{llll}\mathrm{CsF} & \mathrm{HF} & \mathrm{XeF}_{2} & \mathrm{BF}_{3}\end{array}$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 23

Draw one Lewis structure for each of the following compounds; show all unshared electron pairs. None of the atoms in the compounds bears a formal charge, and all atoms have octets (hydrogens have duets).
(a) $\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}$
(b) ketene, $\mathrm{C}_{2} \mathrm{H}_{2} \mathrm{O},$ which has a carbon-carbon double bond
(c) acetonitrile, $\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{~N},$ which has a carbon-nitrogen triple bond

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 24

Draw two Lewis structures for a compound with the formula $\mathrm{C}_{4} \mathrm{H}_{10}$. No atom bears a charge, and all carbons have complete octets.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 25

Give the formal charge on each atom and the net charge on each species in the following structures. All unshared valence electrons are shown.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 26

Give the electronic configuration of (a) the chlorine atom;
(b) the silicon atom (Si); (c) the argon atom;
(d) the magnesium atom. Indicate the valence electrons and the valence orbitals of $\mathrm{Si}$.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 27

Which of the following orbitals is (are) not permitted by the quantum theory of the hydrogen atom? Explain.
$\begin{array}{lllll}2 s & 6 s & 5 d & 2 d & 3 p\end{array}$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 28

Predict the approximate bond angles in each of the following molecules, and explain your reasoning.
(a) :CH $_{2}$
(b) $\mathrm{BeH}_{2}$
(c) ${ }^{+} \mathrm{CH}_{3}$
(d) $: \ddot{\mathrm{Cl}}_{4} \mathrm{Si}$
(e) $\ddot{\mathrm{O}}=\mathrm{\textrm{O }}^{+}-\ddot{\mathrm{O}} \overline{:}^{-}$
$
\begin{aligned}
&\text { (f) } \mathrm{H}_{2} \mathrm{C}=\mathrm{C}=\mathrm{CH}_{2} \quad \text { (Give } \mathrm{H}-\mathrm{C}-\mathrm{C} \text { and }\\
&\mathrm{C}-\mathrm{C}-\mathrm{C} \text { angles. })
\end{aligned}
$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 29

Estimate each of the bond angles and order the bond lengths (smallest first) in the following molecule. State any points of ambiguity and explain.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 30

(a) Construct a hybrid-orbital picture for the hydronium ion $\left(\mathrm{H}_{3} \mathrm{O}^{+}\right)$ using oxygen $s p^{3}$ -hybridized orbitals.
(b) How would you expect the $\mathrm{H}-\mathrm{O}-\mathrm{H}$ bond angles in hydronium ion to compare with those in water (larger or smaller)? Explain.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 31

The allyl cation can be represented by the following resonance structures.
$$
\left[\mathrm{H}_{2} \mathrm{C}-\mathrm{C}=\mathrm{CH}_{2} \stackrel{\mathrm{H}}{\longleftrightarrow} \stackrel{\mathrm{H}}{\mathrm{H}} \mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2}^{+}\right]
$$
(a) What is the bond order of each carbon-carbon bond in the allyl cation?
(b) How much positive charge resides on each carbon of the allyl cation?
(c) Although the preceding structures are reasonable descriptions of the allyl cation, the following cation cannot be described by analogous resonance structures. Explain why the structure on the right is not a reasonable resonance structure.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 32

Consider the resonance structures for the carbonate ion.
(a) How much negative charge is on each oxygen of the carbonate ion?
(b) What is the bond order of each carbon-oxygen bond in the carbonate ion?

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 33

(a) Two types of nodes occur in atomic orbitals: spherical surfaces and planes. Examine the nodes in $2 s, 2 p,$ and $3 p$ orbitals, and show that they agree with the following statements:
1. An orbital of principal quantum number $n$ has $n-1$ nodes.
2. The value of $m_{l}$ gives the number of planar nodes.
(b) How many spherical nodes does a $5 s$ orbital have? A $3 d$ orbital? How many nodes of all types does a $3 d$ orbital have?

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 34

The shape of one of the five energetically equivalent $3 d$ orbitals follows. From your answer to Problem 1.33 , sketch the nodes of this $3 d$ orbital, and associate a wave peak or a wave trough with each lobe of the orbital. (Hint: It doesn't matter where you put your first peak; you should be concerned only with the relative positions of peaks and troughs.)

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 35

Sketch a $4 p$ orbital. Show the nodes and the regions of wave peaks and wave troughs. (Hint: Use Fig. 1.11 and the descriptions of nodes in Problem 1.33a.)

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 36

Account for the fact that $\mathrm{H}_{3} \mathrm{C}-\mathrm{Cl}$ (dipole moment $1.94 \mathrm{D}$ ) and $\mathrm{H}_{3} \mathrm{C}-\mathrm{F}$ (dipole moment $1.82 \mathrm{D}$ ) have almost identical dipole moments, even though fluorine is considerably more electronegative than chlorine.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 37

(a) Draw an appropriate bond dipole for the carbon magnesium bond in dimethylmagnesium.
(b) What is the geometry of dimethylmagnesium? Explain.
(c) What conclusion can you draw about the dipole moment of dimethylmagnesium?

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 38

The principles for predicting bond angles do not permit a distinction between the following two conceivable forms of ethylene.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 39

(a) Give the $\mathrm{H}-\mathrm{C}=\mathrm{O}$ bond angle in methyl formate.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 39

(a) Give the $\mathrm{H}-\mathrm{C}=\mathrm{O}$ bond angle in methyl formate.
(b) One dihedral angle in methyl formate is the angle between the plane containing the $\mathrm{O}=\mathrm{C}-\mathrm{O}$ bond and the plane containing the $\mathrm{C}-\mathrm{O}-\mathrm{C}$ bonds. (Notice that one bond is common to both.) Sketch the two structures of methyl formate: one in which this dihedral angle is $0^{\circ}$ and the other in which it is $180^{\circ}$

Anand Jangid

Numerade Educator

Problem 40

A well-known chemist, Havno Szents, has heard you apply the rules for predicting molecular geometry to water; you have proposed (Problem $1.9 \mathrm{~b}, \mathrm{p} .18$ ) a bent geometry for this compound. Dr. Szents is unconvinced by your arguments and continues to propose that water is a linear molecule. He demands that you debate the issue with him before a distinguished academy. You must therefore come up with experimental data that will prove to an objective body of scientists that water indeed has a bent geometry. Explain why the dipole moment of water, $1.84 \mathrm{D},$ could be used to support your case.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 41

Use your knowledge of vectors to explain why, even though the $\mathrm{C}-\mathrm{Cl}$ bond dipole is large, the dipole moment of carbon tetrachloride, $\mathrm{CCl}_{4},$ is zero.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 42

Three possible dihedral angles for $\mathrm{H}_{2} \mathrm{O}_{2}\left(0^{\circ}, 90^{\circ},\right.$ and $\left.180^{\circ}\right)$ are shown in Fig. 1.6 on p. $19 .$
(a) Assume that the $\mathrm{H}_{2} \mathrm{O}_{2}$, molecule exists predominantly in one of these arrangements. Which of the dihedral angles can be ruled out by the fact that $\mathrm{H}_{2} \mathrm{O}_{2}$ has a large dipole moment $(2.13 \mathrm{D}) ?$ Explain.
(b) The bond dipole moment of the $\mathrm{O}-\mathrm{H}$ bond is tabulated as $1.52 \mathrm{D}$. Use this fact and the overall dipole moment of $\mathrm{H}_{2} \mathrm{O}_{2}$ in part
(a) to decide on the preferred dihedral angles in $\mathrm{H}_{2} \mathrm{O}_{2} .$ Take the $\mathrm{H}-\mathrm{O}-\mathrm{O}$ bond angle to be the known value $\left(96.5^{\circ}\right) .$ (Hint: Apply the law of cosines.)

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 43

Given the dipole moment of water $(1.84 \mathrm{D})$ and the $\mathrm{H}-\mathrm{O}-\mathrm{H}$ bond angle $\left(104.45^{\circ}\right)$, justify the statement in Problem 1.42b that the bond dipole moment of the $\mathrm{O}-\mathrm{H}$ bond is $1.52 \mathrm{D}$.

Aarti Kumari

Numerade Educator

Problem 44

Bring two $2 s$ orbitals together to a bonding distance. (The wave troughs will overlap at this distance.) Form bonding and antibonding molecular orbitals, and show the electron occupancy diagram for the $\mathrm{Li}_{2}$, molecule.

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 44

Bring two $2 s$ orbitals together to a bonding distance. (The wave troughs will overlap at this distance.) Form bonding and antibonding molecular orbitals, and show the electron occupancy diagram for the $\mathrm{Li}_{2}$, molecule.

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 45

Consider two $2 p$ orbitals, one on each of two atoms, oriented head-to-head as in Figure P1.45. Imagine bringing the nuclei closer together until the two wave peaks (the blue lobes) of the orbitals just overlap, as shown in the figure. A new system of molecular orbitals is formed by this overlap.
(a) Sketch the shape of the resulting bonding and antibonding molecular orbitals.
(b) Identify the nodes in each molecular orbital.
(c) Construct an orbital interaction diagram for molecular orbital formation.
(d) If two electrons occupy the bonding molecular orbital, is the resulting bond a $\sigma$ bond? Explain.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 46

Consider two $2 p$ orbitals, one on each of two different atoms, oriented side-to-side, as in Figure P1.46. Imagine bringing these nuclei together so that overlap occurs as shown in the figure. This overlap results in a system of molecular orbitals.
(a) Sketch the shape of the resulting bonding and antibonding molecular orbitals.
(b) Identify the node(s) in each.
(c) Construct an orbital interaction diagram for molecular orbital formation.
(d) When two electrons occupy the bonding molecular orbital, is the resulting bond a $\sigma$ bond? Explain.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 47

In this problem we'll construct the molecular orbitals of the dioxygen molecule $\left(\mathrm{O}_{2}\right) .$ Imagine bringing two oxygen atoms to within a bonding distance along the $x$ axis (the horizontal axis in the plane of the page), and imagine the molecular orbitals that would form from overlap of the valence atomic orbitals.
(a) Sketch the bonding and antibonding combinations $(2 s \sigma$
atomic orbitals interact. Show the nodes. (Hint: See Problem 1.44.)
(b) Sketch the bonding and antibonding combinations $(2 p \sigma$ and $2 p \sigma^{*}$ ) that result when the $2 p_{x}$ atomic orbitals overlap. (Note again that the $x$ axis is the horizontal axis in the plane of the page.) Show the nodes. (Hint: See Problem 1.45.)
(c) Sketch the bonding and antibonding combinations $\left(2 p \pi_{y}\right.$ and $\left.2 p \pi_{y}^{*}\right)$ that result when the $2 p_{y}$ atomic orbitals overlap. (Assume that the $y$ axis is the vertical axis in the plane of the page.) Show the nodes. (Hint: See Problem 1.46.)
(d) Show that the bonding and antibonding combinations $\left(2 p \pi_{z}\right.$ and $\left.2 p \pi_{z}^{*}\right)$ that result when the $2 p_{z}$ atomic orbitals overlap are identical to the $2 p \pi_{y}$ and $2 p \pi_{y}$ MOs in
(c), but oriented at $90^{\circ}$. (Assume that the $z$ axis is the vertical axis perpendicular to the plane of the page.)
(e) The energy order of these MOs and the component atomic orbitals is
$2 s \sigma<2 s$ (atomic orbitals) $<2 s \sigma^{\text {? }}<2 p \sigma<2 p \pi_{y}=$
$2 p \pi_{z}<2 p$ (atomic orbitals) $<2 p \pi_{y}^{*}=2 p \pi_{z}^{*}<2 p \sigma^{*}$
Construct an orbital interaction energy diagram showing the energy levels of the atomic orbitals along with the energies of these MOs. Add the available valence electrons from two oxygen atoms.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 48

When a hydrogen molecule absorbs light, an electron jumps from the bonding molecular orbital to the antibonding molecular orbital. Explain why this light absorption can lead to the dissociation of the hydrogen molecule into two hydrogen atoms. (This process, called photodissociation, can sometimes be used to initiate chemical reactions.)

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 49

Suppose you take a trip to a distant universe and find that the periodic table there is derived from an arrangement of quantum numbers different from the one on Earth. The rules in that universe are
1. principal quantum number $n=1,2, \ldots$ (as on Earth);
2. angular momentum quantum number $l=0,1,2, \ldots,$ $n-1$ (as on Earth);
3. magnetic quantum number $m_{l}=0,1,2, \ldots, l$ (that is, only positive integers up to and including $l$ are allowed); and
4. spin quantum number $m_{s}=-1,0,+1$ (that is, three allowed values of spin).
(a) Assuming that the Pauli exclusion principle remains valid, what is the maximum number of electrons that can populate a given orbital?
(b) Write the electronic configuration of the element with atomic number 8 in the periodic table.
(c) What is the atomic number of the second noble gas?
(d) What rule replaces the octet rule?

Adriano Chikande

Adriano Chikande

Numerade Educator