Deck 13: Heterocyclic Compounds

Question 1

Which of the following statements about pyridine is false?

A) The nitrogen is basic.
B) Pyridine reacts faster than benzene in electrophilic aromatic substitution reactions.
C) Pyridine can behave as a hydrogen bond acceptor.
D) Pyridine is more polar than benzene.
E) All of pyridine's atoms are sp² hybridized.

Answer 1

Pyridine reacts faster than benzene in electrophilic aromatic substitution reactions.

Question 2

Pyrrole is a weak base because:

A) the nitrogen lone pair is part of the aromatic system.
B) the nitrogen lone pair is in an sp²-hybridized orbital.
C) the nitrogen lone pair is on a highly electronegative atom.
D) the nitrogen lone pair is easily deprotonated
E) the nitrogen lone pair is easily protonated.

Answer 2

the nitrogen lone pair is part of the aromatic system.

Question 3

The structural formula for furan is:

A)
B)
C)
D)
E)

Answer 3

Question 4

The decreasing order of basicity of the following is:

A) 1 > 2 > 3
B) 1 > 3 > 2
C) 3 > 2 > 1
D) 2 > 1 > 3
E) 3 > 1 > 2

Question 5

What type of heterocycle is present in both histamine and histidine?

A) indole
B) pyrimidine
C) purine
D) imidazole
E) thiazole

Question 6

The name of the heterocycle below is:

A) pyrrole
B) furan
C) thiophene
D) pyryllium
E) phenol

Question 7

Which of the following molecules can be classified as a heterocycle?

A)
B)
C)
D)
E)

Question 8

Which of the following is not a heterocyclic compound?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 9

Which of the following statements about the pyrylium ion is false?

A) The pyrylium ion appears as a substructure in many pigments.
B) The pyrylium ion is an example of an aromatic cation.
C) The oxygen lone pair in a pyrylium ion is basic.
D) All atoms in the pyrylium ion (except the hydrogens) are sp²-hybridized.
E) The pyrylium ion will react with nucleophiles.

Question 10

What is the structure of 2,5-dimethylpyrrole?

A)
B)
C)
D)
E)

Question 11

The name of the heterocycle below is:

A) pyrrole
B) furan
C) thiophene
D) pyryllium
E) phenol

Question 12

What type of heterocycle is found in guanine?

A) purine
B) pyrimidine
C) pyridine
D) quinoline
E) oxazole

Question 13

In imidazole,

A) the chemistry is more like a diene than like an aromatic compound.
B) the chemistry is more like an isolated alkene than an aromatic compound.
C) N¹ is more basic than N³.
D) both N³ and N¹ are equally basic.
E) N³ is more basic than N¹.

Question 14

The heterocycle cytosine, found in nucleic acids, is an example of a:

A) purine
B) pyrimidine
C) pyridine
D) piperidine
E) pyrazine

Question 15

To what family of heterocyclic compounds do both serotonin and tryptophan belong?

A) imidazole
B) oxazole
C) thiazole
D) indole
E) pyridazine

Question 16

The structure of quinoline is:

A)
B)
C)
D)
E)

Question 17

Which of the following statements is false?

A) Furan, pyrrole, and thiophene are more reactive than benzene in electrophilic aromatic substitution.
B) Electrophilic substitution in pyridine occurs mainly in the 2- and 4-positions.
C) Electrophilic substitution in furan, pyrrole, and thiophene occurs mainly in the 2-position.
D) Pyridine is more basic than pyrrole.
E) An unshared electron pair on O, N, or S is part of the aromatic $\pi$ system in furan, pyrrole, and thiophene.

Question 18

Pyridine is a weaker base than aliphatic tertiary amines because

A) the N is sp² hybridized in pyridine and sp³ hybridized in aliphatic amines.
B) there are no unshared electrons on the N in pyridine.
C) the electrons on the N in pyridine are delocalized around the ring.
D) the N in pyridine is already protonated.
E) the unshared electron pair on N in pyridine is part of the aromatic $\pi$ system.

Question 19

Which of the following heterocyclic compounds is not aromatic?

A)
B)
C)
D)
E)

Question 20

The name of is:

A) pyrrole
B) furan
C) pyridine
D) pyrimidine
E) thiophene

Question 21

What is the major product of the following reaction?

A)
B)
C)
D)
E)

Question 22

Which of the following compounds will undergo nucleophilic aromatic substitution at the fastest rate?

A)
B)
C)
D)
E)

Question 23

What reagent(s) will accomplish the following transformation?

A) H₂SO₄ in H₂O
B) NaOCH₃ in CH₃OH
C) NaBH₄
D) CH₃I
E) NaOH in H₂O

Question 24

What set of reagents is needed to carry out the following reaction?

A) KMnO₄
B) 3 H₂, Pt
C) NaNH₂, liq.NH₃
D) HCl, H₂O
E) NaOH, H₂O

Question 25

The following reaction occurs by what mechanism?

A) S_N1
B) S_N2
C) nucleophilic acyl substitution
D) nucleophilic aromatic substitution
E) electrophilic aromatic substitution

Question 26

Which of the following compounds will undergo electrophilic aromatic substitution reactions at the fastest rate?

A)
B)
C)
D)
E)

Question 27

The product of the following reaction is

A)
B)
C)
D)
E)

Question 28

An intermediate in the nitration of pyridine is:

A) I
B) II
C) III
D) IV
E) none of the above

Question 29

The first step in the following reaction is:

A) loss of chloride (Cl^-) from C-2 to give a carbocation.
B) displacement of chloride (Cl^-) from C-2 by methoxide (CH₃O^-).
C) base-promoted elimination of HCl from carbons 2 and 3.
D) reduction of the pyridine by methoxide.
E) addition of methoxide to C-2.

Question 30

What is the major product of the following reaction?

A)
B)
C)
D)
E)

Question 31

The final product of the following reaction sequence is:

A)
B)
C)
D)
E)

Question 32

The product of the following reaction is:

A)
B)
C)
D)
E)

Question 33

What reagent is required to accomplish the following transformation?

A) NaBH₄
B) CH₃OH
C) KMnO₄
D) NaOCH₃
E) NaNH₂/NH₃

Question 34

Furfural (2-furaldehyde) is produced by dehydrating a(n):

A) cyclic acid
B) ether
C) hexose
D) pentose
E) triose

Question 35

The product of the following reaction is

A)
B)
C)
D)
E)

Question 36

The major mechanism by which five membered aromatic heterocycles react with electrophiles is:

A) nucleophilic aromatic substitution
B) electrophilic aromatic substitution
C) ionic addition
D) free radical addition
E) oxidation-reduction