Kelter P., Mosher M., Scott A. Chemistry. The Practical Science

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12.15 Organic Chemistry and Modern Drug Discovery

Chemical Applications and Practices

97. The total synthesis of a potential drug requires nine steps,

each with a 95% yield. What is the overall yield of the ﬁnal

drug made from this synthesis?

98. Acetylsalicylic acid, also known as aspirin, is a derivative of

a natural compound found in willow trees. Explain how a

researcher might have originally surmised that an active

substance was to be found in the leaves and bark of the

willow tree.

Comprehensive Problems

99. Why do gasoline manufacturers adjust the gasoline mixture

for automobiles in accordance with the season of the year?

100. Using information from this chapter, describe how the

acidity of salicylic acid, shown below, can be reduced by

modiﬁcation of the compound via a chemical reaction.

101. Gasoline is delivered to a farmer for use in the farm’s

combines. A cylindrical storage tank with a circumference

of 6.0 ft is used to store the gasoline until it is used. The

farmer uses a yardstick to measure the depth of the gasoline

in the storage tank.

a. How many gallons of gasoline are in the tank if the

yardstick measures the gasoline to a depth of 22 inches?

b. 2,3-dimethylhexane is one of the components in the

gasoline. Draw the structure of this compound.

102. The compound responsible for the odor of wintergreen was

discussed in the chapter.

a. What two compounds (an alcohol and a carboxylic

acid) could be condensed to prepare methyl salicylate?

b. If a company that manufactures a muscle pain relief

cream requires 352 kg of methyl salicylate, how many

liters of the alcohol would be needed? (Assume the

density of the alcohol is 0.789 g/mL.)

Salicylic acid

COH

103. In Table 12.5, we mention that one of the fractions distilled

from crude oil is known as petroleum ether. This fraction is

used in the organic research lab to recrystallize reaction

products.

a. Draw and name at least two compounds that could be

found in this distillation fraction.

b. Why does the name of this fraction appear to be a

misnomer?

104. The addition of a halogen to an alkene is a good way to pro-

duce an alkyl halide in the laboratory. But often, a researcher

is interested in adding only one halogen atom to the com-

pound. In such a case, a hydrogen halide is used for the addi-

tion reaction.

a. If a research student ﬁlls a 2.5 L ﬂask with 0.25 g gaseous

hydrogen chloride and 0.48 g of gaseous trans-2-butene,

what mass of the addition product can be made?

b. What is the name of that product?

c. What is the concentration, in molarity, of the product in

the ﬂask?

105. The organic chemistry industry of the late part of the 1800s

was interested in creating new dyes for fabrics.

a. What features of an organic compound would make it

suitable for use as a dye?

b. If a particular organic dye was yellow in color, what

range of wavelengths would be reﬂected by the

compound?

c. What range of energies, in kJ/mol, is associated with

these wavelengths?

Thinking Beyond the Calculation

106. An unknown organic compound is identiﬁed. Reaction of

this unknown with two molecules of ethanol produces a

diester. The unknown organic compound can be prepared

by oxidizing 1,2-ethanediol.

a. What is the structure of the unknown?

b. What properties (chemical and physical) would you

predict this unknown to possess?

c. If 10 g of the unknown produce 10 g of the diester, what

is the percent yield of the reaction?

d. When the diester is placed in aqueous solution

containing a small amount of catalyst, the solution

becomes acidic. Provide a balanced reaction that

explains this result.

e. A polymer can be made when the unknown organic

compound is condensed with ethylene glycol

(HOCH

OH). Draw the structure of this polymer.

538 Chapter 12 Carbon

539

Contents and Selected Applications

Chemical Encounters: Materials in the Hospital

13.1 The Structure of Crystals

Chemical Encounters: X-ray Crystallography

13.2 Metals

Chemical Encounters: Photovoltaic Devices

Chemical Encounters: Dental Amalgams

13.3 Ceramics

Chemical Encounters: Magnetic Resonance Imaging

13.4 Plastics

13.5 Thin Films and Surface Analysis

Chemical Encounters: Heart Deﬁbrillators

13.6 On the Horizon—What Does the Future Hold?

Chemical Encounters: “Green Chemistry”

Modern

Materials

Modern materials affect our lives every

day. Their use in bulletproof vests, auto-

mobiles, and computers saves and pro-

tects us from harm. And, without their

use in the health care industry, we would

surely suffer. Let’s examine a trip to the

hospital to see how modern materials

are used.

Go to college.hmco.com/pic/kelterMEE for online learning resources.

540

A trip to the hospital offers interesting insight

into the products of chemistry. Look around and

you’ll see chemistry that is central to the mission of

the hospital and to the quality of our lives. The emergency

room (ER) nurse who gives an injection, the radiologist who uses

the magnetic resonance imager (MRI), and the doctor who replaces a

hip joint all depend on the products of materials science to do their jobs.

Materials science is concerned with the chemistry and development of substances

employed to make the items we use everyday. What types of materials do you see in the

hospital? The emergency room syringe is made of plastic, as are the bag and the tubing

that holds the intravenous (IV) ﬂuid. The hospital MRI requires a powerful magnetic ﬁeld

generated with a special type of ceramic material called a superconductor. Hip replace-

ments are often made from metal alloys and plastic polymers that are stronger than the

bone they replace. Each of these products (the plastic, the superconductor, and the metal

alloy) is a recently developed material.

In this chapter we will discuss the chemical features of modern materials. Knowing

about bonding in solids, the properties of metals, and substances called liquid crystals will

lead us to a better understanding of materials science. Along the way, we’ll discover some

new materials that are of great practical use, and we’ll ﬁnd out that the old materials we

know are also part of the ﬁeld of materials science. Because many of the modern materials

are solids, we begin our study of modern materials with the structure of crystals.

Application

HEMICAL

ENCOUNTERS:

Materials in the

Hospital

13.1 The Structure of Crystals

Sodium chloride (table salt) plays an important role in our diet. Medical workers

recognize the essential role that sodium plays in maintaining blood pressure,

allowing the transmission of nerve signals and the transporting of nutrients into

cells. When a nurse reaches for an intravenous saline solution, a bag of sterile

0.9% (w/v) sodium chloride is what she or he gets. Why choose a solution of

sodium chloride? Blood contains 0.9% (w/v) sodium chloride, and this concen-

tration keeps the blood in a patient at the same osmotic pressure (Chapter 11).

An IV saline solution.

Application

Crystalline solid

13.1 The Structure of Crystals 541

In Chapter 8, we discussed the formation of sodium chloride from its elements.

We noted the strength of the ionic bond by focusing on the lattice energy,

786 kJ/mol. To learn more about sodium chloride and other crystalline ionic

compounds, however, we need to explore how the ions come together to make an

ionic crystal. What can the shape of an ionic solid tell us? Knowing the locations

of the ions within an ionic solid enables us to determine the density, the nature

(crystalline or amorphous), and the properties of the solid (see Table 13.1).

Types of Solids

Why are some compounds, such as table salt or sugar, solid rather than liquid or

gaseous under normal conditions? The atoms, ions, or molecules of a solid are

not free to move signiﬁcantly relative to each other. The materials are solids

because the intermolecular forces of attraction are strong enough to hold the par-

ticles in a rigid structure. In a

crystalline solid (Figure 13.1), the atoms, ions, or

molecules are highly ordered in repeating units over long ranges. Although they

have fairly rigid and ﬁxed locations of the atoms, ions, or molecules,

amorphous

solids

such as the glass in a window pane lack the high degree of long-range order

(they still have short-range order) found in a crystalline solid. Sodium chloride is

an example of a crystalline solid (Figure 13.2), because it has an ordered structure

with ﬁxed locations for the sodium and chloride ions.

Different Types of Solids and Their Properties

Type of Particles Forces Between

Solid in Solid Particles Physical Properties Examples

Ionic Cations and Electrostatic Hard and brittle, high melting point, NaCl,

anions attraction poor thermal and electrical CaO,

conductivity MgBr

Molecular Atoms or London dispersion, Fairly soft, low to moderate CH

molecules dipole–dipole, and/or melting point, poor thermal and C

(glucose),

hydrogen bonding electrical conductivity H

O, Kr

Network Atoms Covalent bonds Very hard, very high melting point, C (diamond),

covalent typically poor thermal and SiO

(quartz),

electrical conductivity SiC, BN

Metallic Atoms Metallic bond Soft to hard, low to high melting Na, Fe, Au, Ag, Al

point, good thermal and

electrical conductivity

TABLE 13.1

Amorphous solid

FIGURE 13.1

Solids can be crystalline or

amorphous.

Unit cell

= Cl

–

= Na

Formula

unit (NaCl)

= Cl

–

= Na

FIGURE 13.2

Crystals of sodium chloride.

Video Lesson: Types of Solids

Glucose

What does a crystal look like? Try using a magnifying glass or microscope to

look at crystals of table salt or sugar. These two crystalline solids appear as solid

cubes, whereas other solids take the shape of needles, plates, and a host of other

faceted designs. The shape of the crystal you see is a result of the way in which the

atoms and ions are arranged at the atomic level, known as the crystalline lattice.

Some solids, such as table salt (NaCl), are

ionic solids, made up of ionic com-

pounds held together by strong electrostatic forces of attraction between adjacent

cations and anions. Because these forces are formidable, the ionic solids typically

have high melting points. Solutions made from ionic solids conduct electricity, as

we saw in Chapter 4. We referred to them as electrolytes.

On the other hand, some solids, such as glucose (C

), are molecular

solids

, made up of molecules held in a rigid structure. Despite the structural sim-

ilarity to an ionic solid, the intermolecular forces of attraction between adjacent

molecules are not as strong as the electrostatic forces found in ionic solids. There-

fore, melting points of the molecular solids are not very high. In addition,

because most molecules do not dissociate into ions when they are dissolved, so-

lutions made from molecular solids typically do not conduct electricity. As we’ll

see in this chapter, the properties of molecular and ionic solids are different in

other important ways.

Crystal Lattices

A structure known as a crystal lattice deﬁnes the shapes of crystalline solids. This

crystal lattice marks the position each of the atoms, ions, or molecules within the

crystal. The 3-D grid comprises three pairs of parallel planes that intersect to

makeparallelepipeds (three-dimensional boxes),and in Figure13.3 we see that re-

peating the parallelepiped in three dimensions gives us the lattice for a crystal.

The simplest parallelepiped that can be repeated to produce the entire crystal lat-

tice is the

unit cell (the smallest repeating unit of the lattice). In other words, the

unit cell is the smallest repeating unit of atoms, ions, or molecules that would

describe the entire crystal.Whenever possible, we try to arrange the corners of the

lattice so that they line up with the centers of the atoms, ions, or molecules in

the solid.

If the parallel sets of planes intersect at right angles to make a cube (as they do

in Figure 13.3), the lattice is known as a cubic lattice. The most basic of the cubic

lattices is made up of the

simple cubic unit cell (also known as the primitive unit

cell), in which the centers of the atoms, ions, or molecules are located only on the

corners of the unit cell. Polonium, a radioactive metal that shows promise as a

thermoelectric power source in space satellites, crystallizes in the simple cubic

structure. The presence of an additional atom, ion, or molecule at the center of

542 Chapter 13 Modern Materials

FIGURE 13.3

Parallelopiped in a cubic lattice.

Visualization: Network Solids

Visualization: Molecular Solids

13.1 The Structure of Crystals 543

Simple cubic

Body-centered cubic

Face-centered cubic

(c)

(b)

(a)

Unit cell Lattice structure Space-filling unit cell Example

Polonium

metal

Uranium

metal

Gold

metal

FIGURE 13.4

Cubic unit cells.

the simple cubic unit cell gives a body-centered cubic (bcc) unit cell. Iron metal

crystallizes as a body-centered cubic structure. If an atom, ion, or molecule is lo-

cated on each of the faces of the cubic lattice, the lattice is called a

face-centered

cubic (fcc) unit cell

. When cooled below –182°C, methane (the gas that heats many

homes) forms crystals that have a face-centered cubic structure. Figure 13.4 illus-

trates each of the unit cells in the cubic lattice group.

Metallic Crystals

Solid metals are made up of atoms of an element arranged in a crystalline lattice.

If we imagine that the atoms are hard spherical balls, we can get a picture of how

they might be arranged into a crystal. We can visualize this by placing marbles in

a box. Put in just enough marbles to cover the bottom and what happens. To

Video Lesson: Crystal Packing

utilize most efﬁciently all of the space available, the marbles adopt a staggered

arrangement. The way they pack is called a

closest packed structure (Figure 13.5).

What if we want to completely ﬁll a box with marbles? The second layer is also

staggered, but it occupies the dimples in the ﬁrst layer. However, there are differ-

ent ways in which we can stack the third and subsequent layers of marbles. It is

the placement of this third layer that determines the type of packed structure that

results. If the third layer is placed in such a way that it lines up with the ﬁrst layer,

what results is a

hexagonal closest packed (hcp) structure whose unit cell is a

hexagonal prism (Figure 13.6). Magnesium and zinc atoms form hexagonal clos-

est packed solids. If the third layer is staggered in the same fashion as the second

layer, so that it doesn’t line up with the ﬁrst layer, we obtain the

cubic closest

packed (ccp) structure

(Figure 13.7). Metals, such as gold, silver, and copper, adopt

this structure and have face-centered cubic unit cells.

EXERCISE 13.1 Matching

Match each of the following metals with the ﬁgure that best represents its structure.

a. copper (fcc) b. iron (bcc) c. iron (hcp)

Solution

Copper (face-centered cubic) is B. Iron (body-centered cubic) is C, and iron (hexag-

onal closest packed) is A.

PRACTICE 13.1

Provide a diagram for each of the following elements in the given unit cell.

a. manganese (simple cubic) b. nickel (fcc) c. tungsten (bcc)

See Problems 5 and 6.

544 Chapter 13 Modern Materials

A B C

FIGURE 13.7

Cubic closest packed structure.

FIGURE 13.5

Closest packed arrangement

of spheres in two dimensions.

FIGURE 13.6

Hexagonal closest packed

structure.

Some metals do not form closest packed structures. For instance, the alkali

metals stack together into body-centered cubic unit cells. Although we can know

how a metal packs into a particular crystalline lattice, the reason why metals pack

in the way they do is not well understood. Predicting the crystalline lattice struc-

ture of a metal is difﬁcult.

Why is it useful to know the structure of the unit cell?

One answer has to do with the enzymes within us. Read on.

HERE’S WHAT WE KNOW SO FAR

■

Solids can be either amorphous or crystalline.

■

Crystalline solids result from highly structured packing of the material.

■

The arrangement of particles within the crystal is as a repeating unit called the

unit cell.

■

The simple cubic, body-centered cubic, and face-centered cubic are examples

of unit cells.

■

In addition, substances can also pack into closest packed structures, which in-

clude the hexagonal closest packed and the cubic closest packed structures.

Crystallography and the Unit Cell

In 1997, the Nobel Prize in chemistry was awarded to Paul D. Boyer, John E.

Walker, and Jens C. Skou “for their elucidation of the enzymatic mechanism un-

derlying the synthesis of adenosine triphosphate (ATP).” Essential to their dis-

covery was the identiﬁcation of the crystalline structure of an enzyme found in

cows, bovine F1 ATP synthase (Figure 13.8). By determining the structure of this

enzyme, the researchers were able to understand how ATP (a source of energy in

living things) is made. This is just one example of the utility of knowing the crys-

tal structure of a solid. Medical researchers use crystal structures to get a clear

picture of the location where reactions take place, which is called the “active site”

of the enzyme. This information makes it possible to de-

sign drugs that will best inﬂuence the activity of the en-

zyme. For instance, the structure of the active site of

HMG-CoA reductase (an enzyme that makes choles-

terol) was used in the development of Rosuvastatin, a

drug that binds to the enzyme and helps slow the forma-

tion of cholesterol. The binding of Rosuvastatin leads to

lower serum cholesterol levels in patients.

The structures of these enzymes were determined by

X-ray crystallography. How does this technique help us

determine the structure of a crystal? We begin by exam-

ining the behavior of light. When light waves pass

through a grating (a series of closely spaced narrow slits),

13.1 The Structure of Crystals 545

FIGURE 13.8

Cartoon of the crystal structure of bovine F1 ATP synthase. Because

there are so many atoms in this enzyme, each strand of the protein is

represented as a ribbon of a different color. Speciﬁc atoms are not

included in the structure.

p_13_08

A single light beam from a laser, when passed through a narrow

opening, makes a pattern of dots due to constructive and destructive

interference of the individual photons.

Application

constructive and destructive interference of the waves produces a pattern of light

and dark regions. This

diffraction pattern can be used to determine the position

and widths of the slits. The most useful diffraction pattern occurs when the wave-

length of the light is similar to the widths of the slits. In X-ray crystallography, a

diffraction pattern is generated by using a crystal instead of a series of slits.

Look at the unit cells of the crystals mentioned in the previous section. In-

stead of slits, the unit cells contain a lot of empty space. Because the spaces in the

crystal are on the order of 100 picometers (1 pm = 10

–12

m), radiation of similar

wavelengths is used. X-rays—electromagnetic radiation with wavelengths

near 100 pm—are directed through the crystal and are diffracted as shown in

Figure 13.9. The resulting pattern of high- and low-intensity X-rays is used to de-

termine the position and size of the atoms in the crystal. Our ability to calculate

the positions of the atoms from the crystal diffraction pattern is based on the

work of William Henry Bragg (1862–1942) and William Lawrence Bragg

(1890–1972), a father-and-son team who shared the Nobel Prize in physics in

1915 for their work in X-ray crystallography.

Electromagnetic radiation can pass through a crystal because of the existence

of empty spaces in the unit cell.

How much empty space is there in a crystal? We

talk about how the spheres are packed as closely together as possible, but in our

unit cells we seem to have a lot of gaps. To determine the amount of empty space,

we need to know how much space the atoms in a unit cell occupy and how much

space the entire unit cell occupies. The difference between these two values is

the empty space. How many complete atoms occupy the unit cell? To simplify the

process, consider the atoms as hard spheres. Figure 13.10 shows the bcc unit cell,

which contains one complete atom in the center of the unit cell. At the corners of

the cell are

⁄8 “pieces” of atoms. Because there are eight corners in the unit cell,

there must be the equivalent of one complete atom. The unit cell for a body-

centered cubic structure contains two complete atoms: the central one and the

eight

⁄8’s that make up the corners. We can go through a similar process for the

primitive cell (one complete atom) and the face-centered cubic cell (four com-

plete atoms).

546 Chapter 13 Modern Materials

FIGURE 13.9

A pattern of reﬂected X-rays is captured

after interaction with a crystal. The

location of the dots in this diffraction

pattern can be used to determine the

structure of a compound.

(b) (c)

(a)

(

)

1 atom + 8 parts 2 atoms

FIGURE 13.10

Body-centered cubic unit cell.

Application

HEMICAL ENCOUNTERS:

X-ray Crystallography

Video Lesson: Crystal Structure

Because we can determine how many atoms occupy a unit cell, knowing the

volume of the unit cell enables us to ﬁnd the amount of empty space in the cell.

What is the volume of a unit cell? We can calculate this for each type of unit cell.

In the face-centered cubic unit cell (Figure 13.11), we see that the diagonal across

one face of the cube is 4 times the radius of the atom (4r) and that the height and

width of the cell are the same distance (d). To ﬁnd the length d, we use the

Pythagorean Theorem (a

+ b

= c

) and solve for the distance:

+ d

= (4r)

= 16r

= 8r

d = r

√

8 = 2.828r

Therefore, the distance along one of the faces of the fcc unit cell is 2.828 times the

radius of the atoms. Note that the distance along the edge of the unit cell is greater

than twice the radius of the atoms. This implies, correctly, that the atoms in the

corners of the unit cell do not touch the atoms in the other corners.

The volume of any parallelepiped is determined by multiplying the length times

the width times the height. For the fcc unit cell, the volume would then be

√

,or

22.63r

. To illustrate this equation, gold metal crystallizes in the cubic closest

packed structure (with fcc unit cells). The volume of the unit cell for gold metal

whose radius is 144 pm is

r = 144 pm

Volume

= (144

√

= 6.76 ×10

EXERCISE 13.2 There’s a Lot of Room in Here

Copper, silver, and gold are known as the coinage metals because of their use in

making coins. Each of these metals forms a face-centered cubic solid. What per-

centage of a fcc unit cell is occupied by empty space?

13.1 The Structure of Crystals 547

Volume = a × b × c

The volume of any parallelipiped is

equal to the height times the width

times the length.

(d)

6 parts + 8 parts 4 atoms

(b) (c)(a)

FIGURE 13.11

Face-centered cubic unit cell.