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Chapter 5: Stereochemistry at Tetrahedral Centers

Every problem in the chapter beside the book’s answer, a chapter at a time as you scroll.

Chapter 5: Stereochemistry at Tetrahedral Centers

25 problems · 43 figures

5-1 §5.2 source ↗

Which of the following objects are chiral?

(a) Soda can (b) Screwdriver (c) Screw (d) Shoe

Answer

Chiral: screw, shoe

5-2 §5.2 source ↗

Which of the following molecules are chiral? Identify the chirality center(s) in each.
(a)
(b)
(c)

Answer (3 parts)

(a)
(b)
(c)

5-3 §5.2 source ↗

Alanine, an amino acid found in proteins, is chiral. Draw the two enantiomers of alanine using the standard convention of solid, wedged, and dashed lines.

Answer

5-4 §5.2 source ↗

Identify the chirality centers in the following molecules (gray = H, black = C, red = O, green = Cl, yellow-green = F):
(a)
(b)

Answer (2 parts)

(a)
(b)

5-5 §5.3 source ↗

Is cocaine (Worked Example 5.2) dextrorotatory or levorotatory?

Answer

Levorotatory

5-6 §5.3 source ↗

A 1.50 g sample of coniine, the toxic extract of poison hemlock, was dissolved in 10.0 mL of ethanol and placed in a sample cell with a 5.00 cm pathlength. The observed rotation at the sodium D line was +1.21°. Calculate [α]D for coniine.

Answer

+16.1°

5-7 §5.5 source ↗

Which member in each of the following sets ranks higher?
(a)
−H or −Br
(b)
−Cl or −Br
(c)
−CH3 or −CH2CH3
(d)
−NH2 or −OH
(e)
−CH2OH or −CH3
(f)
−CH2OH or −CH = O

Answer (6 parts)

(a)
−Br
(b)
−Br
(c)
−CH2CH3
(d)
−OH
(e)
−CH2OH
(f)
−CH = O

5-8 §5.5 source ↗

Rank each of the following sets of substituents:
(a)
−H, −OH, −CH2CH3, −CH2CH2OH
(b)
−CO2H, −CO2CH3, −CH2OH, −OH
(c)
−CN, −CH2NH2, −CH2NHCH3, −NH2
(d)
−SH, −CH2SCH3, −CH3, −SSCH3

Answer (4 parts)

(a)
−OH, −CH2CH2OH, −CH2CH3, −H
(b)
−OH, −CO2CH3, −CO2H, −CH2OH
(c)
−NH2, −CN, −CH2NHCH3, −CH2NH2
(d)
−SSCH3, −SH, −CH2SCH3, −CH3

5-9 §5.5 source ↗

Orient each of the following drawings so that the lowest-ranked group is toward the rear, and then assign R or S configuration:
(a)
(b)
(c)

Answer (3 parts)

(a)
S
(b)
R
(c)
S

5-10 §5.5 source ↗

Assign R or S configuration to the chirality center in each of the following molecules:
(a)
(b)
(c)

Answer (3 parts)

(a)
S
(b)
S
(c)
R

5-11 §5.5 source ↗

Draw a tetrahedral representation of (S)-2-pentanol (2-hydroxypentane).

Answer

5-12 §5.5 source ↗

Assign R or S configuration to the chirality center in the following molecular model of the amino acid methionine (blue = N, yellow = S):

Answer

S

5-13 §5.6 source ↗

One of the following molecules (a)–(d) is D-erythrose 4-phosphate, an intermediate in the Calvin photosynthetic cycle by which plants incorporate CO2 into carbohydrates. If D-erythrose 4-phosphate has R stereochemistry at both chirality centers, which of the structures is it? Which of the remaining three structures is the enantiomer of D-erythrose 4-phosphate, and which are diastereomers?

(a) (b) (c) (d)

Answer

Compound (a) is D-erythrose 4-phosphate, (d) is its enantiomer, and (b) and (c) are diastereomers.

5-14 §5.6 source ↗

How many chirality centers does morphine have? How many stereoisomers of morphine are possible in principle?

Answer

Five chirality centers and 25 = 32 stereoisomers

5-15 §5.6 source ↗

Assign R or S configuration to each chirality center in the following molecular model of the amino acid isoleucine (blue = N):

Answer

S,S

5-16 §5.7 source ↗

Which of the following structures represent meso compounds?
(a)
(b)
(c)
(d)

Answer

Compounds (a) and (d) are meso.

5-17 §5.7 source ↗

Which of the following have a meso form? (Recall that the -ol suffix refers to an alcohol, ROH.)

(a) 2,3-Butanediol (b) 2,3-Pentanediol (c) 2,4-Pentanediol

Answer

Compounds (a) and (c) have meso forms.

5-18 §5.7 source ↗

Does the following structure represent a meso compound? If so, indicate the symmetry plane.

Answer

5-19 §5.8 source ↗

Suppose that acetic acid (CH3CO2H) reacts with (S)-2-butanol to form an ester (see Worked Example 5.6). What stereochemistry would you expect the product(s) to have? What is the relationship of the products?

Answer

The product is pure S-ester. No new chirality centers are formed during the reaction, and the configuration at the chirality center of (S)-2-butanol is unchanged.

5-20 §5.8 source ↗

What stereoisomers would result from reaction of (±)-lactic acid with (S)-1-phenylethylamine, and what is the relationship between them?

Answer

Two diastereomeric salts: (R)-lactic acid plus (S)-1-phenylethylamine and (S)-lactic acid plus (S)-1-phenylethylamine

5-21 §5.9 source ↗

What kinds of isomers are the following pairs?
(a)
(S)-5-Chloro-2-hexene and chlorocyclohexane
(b)
(2R,3R)-Dibromopentane and (2S,3R)-dibromopentane

Answer (2 parts)

(a)
Constitutional isomers
(b)
Diastereomers

5-22 §5.11 source ↗

Identify the indicated hydrogens in the following molecules as pro-R or pro-S:
(a)
(b)

Answer (2 parts)

(a)
(b)

5-23 §5.11 source ↗

Identify the indicated faces of carbon atoms in the following molecules as Re or Si:
(a)
(b)

Answer (2 parts)

(a)
(b)

5-24 §5.11 source ↗

The lactic acid that builds up in tired muscles is formed from pyruvate. If the reaction occurs with addition of hydrogen to the Re face of pyruvate, what is the stereochemistry of the product?

Answer

(S)-Lactate

5-25 §5.11 source ↗

The aconitase-catalyzed addition of water to cis-aconitate in the citric acid cycle occurs with the following stereochemistry. Does the addition of the OH group occur on the Re or Si face of the substrate? What about the addition of the H? Do the H and OH groups add from the same side of the double bond or from opposite sides?

Answer

The −OH adds to the Re face of C2, and −H adds to the Re face of C3. The overall addition has anti stereochemistry.

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Problems and answers are adapted from Organic Chemistry: A Tenth Edition by John McMurry, OpenStax, and are used under the CC BY-NC-SA 4.0 licence. Access for free at https://openstax.org/books/organic-chemistry/pages/1-why-this-chapter. Illustrations: Copyright Rice University, OpenStax, under CC BY-NC-SA 4.0 license. This adaptation is released under the same licence, is non-commercial, and is neither affiliated with nor endorsed by OpenStax or Rice University.