Deck 5: Rings

Question 1

Which of these cycloalkanes cannot relieve torsional strain?

A)cyclopropane
B)cyclobutane
C)cyclopentane
D)a and b
E)a and c

Answer 1

cyclopropane

Question 2

What is the relationship between the two structures shown here?

A) They are enantiomeric conformations.
B) They are identical.
C) They are enantiomers.
D) They are diastereomers.
E) They are constitutional isomers.

Answer 2

They are diastereomers.

Question 3

Using the heats of combustion per CH2 given, select the least stable compound in the set.All values are in kcal/mol.

A)A
B)B
C)C
D)D
E)E

Answer 3

A

Question 4

What is the highest-energy conformation of cyclohexane?

A)chair
B)full boat
C)twist boat
D)half chair
E)b and c are identical.

Question 5

Which of the following molecules is chiral?

A) cis-1,2-dimethylcyclopropane
B) trans-1,3-dimethylcyclobutane
C) cis-1,3-dimethylcyclohexane
D) trans-1,4-dimethylcyclohexane
E) trans-1,3-dimethylcyclohexane

Question 6

Which of the following words describes a low-energy conformation of cyclopentane?

A)boat
B)chair
C)envelope
D)half boat
E)twist chair

Question 7

How many signals would appear in the ¹³C NMR spectrum for this molecule?

A) 2
B) 3
C) 4
D) 5
E) 7

Question 8

Assuming 98.85 % of the molecules are in the conformation with the group A equatorial, what is the value of ΔG° for this equilibrium at 25°C? R=1.987 x10^-3 kcal/mol K

A) -2.64 kcal/mol
B) -2.72 kcal/mol
C) 0.228 kcal/mol
D) 2.64 kcal/mol
E) 2.72 kcal/mol

Question 9

Which double Newman projection matches the view of the molecule below along the C(1)-C(6) and C(3)-C(4) bonds?

A)
B)
C)
D)
E)

Question 10

Which of these cycloalkanes is planar in its lowest energy conformation?

A)A
B)B
C)C
D)D
E)All of the above are planar in their lowest energy conformations.

Question 11

What percentage of methylcyclohexane exists in the axial methyl conformation at equilibrium, given that K_eq=19.5 at 25°C? R=1.987 x 10^-3 kcal/mol K

A) 5 %
B) 19.5 %
C) 50 %
D) 95 %
E) 100 %

Question 12

For which of the following do you expect to have the greatest percentage of molecules in the conformation with the substituent in an equatorial position?

A)
B)
C)
D)
E)

Question 13

Consider the two chair conformations of trans-1,3-dimethylcyclohexane. Which of the following statements is/are true?
I. Keq=1
II. The molecule is chiral.
III. The two chair conformations are enantiomers.

A) I
B) I, II
C) I, III
D) I, II, III
E) II, III

Question 14

What type of strain does cyclobutane relieve by puckering?

A)angle
B)torsional
C)van der Waals
D)bond length
E)all of these

Question 15

Which of these structures represents the highest-energy conformation of cyclohexane?

A)
B)
C)
D)
E)

Question 16

Which of the following statements is true about this structure?

A) The two methyl groups are anti.
B) The two methyl groups are gauche.
C) The two methyl groups are eclipsed.
D) The conformation shown is the highest energy conformation for this molecule.
E) The molecule is achiral.

Question 17

The envelope and twist conformations of cyclopentane are lower energy than the planar one because they have

A)smaller bond angles.
B)larger bond angles.
C)fewer eclipsing interactions.
D)more flexibility.
E)no bent bonds.

Question 18

Use the heat of combustion provided to select the most stable compound.All values are in kcal/mole.

A)Cyclooctane, 1269.2
B)Cyclononane, 1429.6
C)Cyclodecane, 1586.8
D)Cycloundecane, 1743.1
E)Cyclobutane, 499.8

Question 19

Which of these compounds can adopt the most stable conformation?

A)
B)
C)
D)
E)

Question 20

After ring flip, what type of position will substituent X occupy?

A)axial, up
B)axial, down
C)equatorial, up
D)equatorial, down
E)It depends on the nature of X.

Question 21

Explain why the chair conformation of cyclohexane is considered to be strain free.

Question 22

Select any and all words that correctly describe the relationship between groups A and B in the structure shown here.
I. anti
II. gauche
III. eclipsed
IV. cis
V. trans

A) I
B) II
C) III
D) I, IV
E) I, V

Question 23

Which structure is fused?

A)
B)
C)
D)
E)

Question 24

Draw the boat conformation of cyclohexane and identify the hydrogens that are the source of van
der Waals strain.

Question 25

Which three-dimensional structure is not one of the chair flips of the given molecule?

A)
B)
C)
D)
E)

Question 26

Select any and all words that correctly describe the relationship between groups A and B in the structure shown here.
I. anti
II. gauche
III. eclipsed
IV. cis
V. trans

A) I
B) II
C) III
D) I and IV
E) II and V

Question 27

Which pair are not chair flips of each other?

A)
B)
C)
D)
E)

Question 28

What is the correct structure for bicyclo[3.3.1]nonane?

A)
B)
C)
D)
E)

Question 29

Which of the structures shown here is a spiro ring system?

A)
B)
C)
D)
E)

Question 30

Which of the following statements is/are true about the equilibrium shown here?
I. Each structure is chiral.
II. Each structure is achiral.
III. Structure A is favored at equilibrium.
IV. Structure B is favored at equilibrium.
V. A and B are enantiomers.
VI. A and B are diastereomers.

A) I, III
B) I, III, VI
C) II, III, VI
D) I, III, V
E) I, IV

Question 31

Draw an energy versus conformation diagram for cyclohexane, showing all structures and their
relative energy levels.

Question 32

Which equilibrium constant must be precisely equal to 1?

A)
B)
C)
D)
E)

Question 33

Draw the chair conformation of cyclohexane and identify all axial and equatorial hydrogens.

Question 34

What is the correct name for the structure shown here?

A) Bicyclopentylcyclohexane
B) Bicyclo[6.2]nonane
C) Bicyclo[6.2.1]undecane
D) Bicyclo[1.2] cyclononane
E) Bicyclo[9.5]undecane

Question 35

How many signals will appear in the ¹³C NMR spectrum for the molecule shown here?

A) 2
B) 3
C) 4
D) 6
E) 8

Question 36

Select any and all words that correctly describe the relationship between groups A and B in the structure shown here.
I. anti
II. gauche
III. eclipsed
IV. cis
V. trans

A) I
B) II
C) III
D) I and V
E) II and V

Question 37

Which of the following statements is true?

A) trans-Decalin cannot undergo ring flip.
B) cis-Decalin cannot undergo ring flip.
C) In trans-decalin, the bridgehead hydrogens are both equatorial.
D) In cis-decalin, the bridgehead hydrogens are both axial.
E) Both a and c.

Question 38

Draw a Newman projection of cyclohexane looking along two C-C bonds that are separated by one carbon.

Question 39

Which of the following structures is trans-decalin?

A)
B)
C)
D)
E)

Question 40

Draw the envelope conformation of cyclopentane, showing all hydrogens.

Question 41

Draw a bond line structure, showing stereochemistry with wedge-and-dash notation, for 1R, 2S, 4R-4-chloro- 1,2 -dimethylcyclohexane.

Question 42

Explain why axial methylcyclohexane and equatorial methylcyclohexane cannot be separated from
each other at room temperature.

Question 43

Draw both chair forms of cis-1,3-dimethylcyclohexane and identify all sources of strain in the less
stable chair conformation.

Question 44

Provide the systematic IUPAC name for the structure shown here.

Question 45

Draw the ring flip of the structure shown here.

Question 46

Explain why the conformer of 5 -methyl-1,3-dixoane with the methyl group axial exists in a higher percentage at equilibrium than the corresponding one for methylcyclohexane. That is, explain why K₂>K_I below.

Question 47

Draw both chair conformations of trans-1-isopropyl-2-methylcyclohexane and identify the more
stable chair conformation.

Question 48

Use Newman projections of the less stable conformer of methylcyclohexane to identify all
interactions that raise its energy relative to the more stable conformer.

Question 49

Draw the two chair conformations of methylcyclohexane.Identify the more stable conformation
and identify the source(s) of strain in the less stable chair conformation.

Question 50

Draw the most stable chair conformation of 1 S, 2 R-1 -tert -butyl-2-methylcyclohexane.

Question 51

Provide the systematic IUPAC name for the structure shown here.

Question 52

Draw the structure of bicyclo[3.2.1]octane.

Question 53

Which molecule do you expect to be more stable, A or B?

Question 54

Draw a Newman projection along the indicated bond of the conformer below.

Question 55

Draw the most stable conformer of the molecule below in three dimensions.

Question 56

Draw the most stable chair conformation of this sugar.

Question 57

Draw the most stable conformer of trans-1-bromo-4-methylcyclohexane in three dimensions.

Question 58

Convert the chair structure shown to a flat bond-line drawing, using wedge-and-dash notation to
show stereochemistry.

Question 59

Provide a name for the structure shown here, including R and S designation of stereogenic
carbons.

Question 60

Draw the most stable conformer of the molecule below in three dimensions.