Deck 26: The Chemistry of the Aromatic Heterocycles and Nucleic Acids

Question 1

Name the heterocycle.

Answer 1

The heterocycle is 3-ethylpyridine.

Question 2

Name the heterocycle.

Answer 2

The heterocycle is 3-nitrothiophene.

Question 3

Draw a structure for each of the compounds.
a. 4-methoxyindole
b. thiophene-2-carboxylic acid

Answer 3

a.
​
b.

Question 4

Draw a structure for each of the compounds.
a. oxazole-5-carbaldehyde
b. 4-methoxypyridine

Question 5

The structure of indole is shown below. Unlike most amines, indole is difficult to protonate. Its conjugate acid has a pK_a of -3.5. Explain why indole is difficult to protonate.

Question 6

An imidazole ring is an important heterocycle found in the amino acid histidine. Draw an orbital configuration of imidazole, showing the 2p orbitals and electrons in each orbital. Use the diagram to explain which electrons are part of the aromatic system and which can be protonated in the presence of an acid.

Question 7

Purine is a bicyclic ring found in DNA. The structure for purine is shown below. For each lone pair of nitrogen, determine whether the lone pair resides on a 2p orbital or sp² orbital.

Question 8

For each heterocycle, label as aromatic, anti-aromatic, or nonaromatic.

Question 9

Circle the nitrogen that is more basic and explain why.

Question 10

Rank the reactivity of these compounds towards electrophilic aromatic substitution, from most reactive to least.
benzene, furan, thiophene, pyrrole, pyridine

Question 11

Predict the major organic product for the reaction.

Question 12

Thiophene undergoes electrophilic aromatic substitution (EAS) with bromine to give two possible regioisomers, A and

Question 13

Outline a synthesis for the transformation:

Question 14

Outline a synthesis for the transformation:

Question 15

Identify the missing reagent(s) for the transformation:

Question 16

2-Halopyridines undergo substitution under milder conditions than the Chichibabin reaction. Write a curved-arrow mechanism for this substitution.

Question 17

Predict the major organic product for this synthetic sequence.

Question 18

In biological systems, pyridoxal phosphate is a cofactor that aids in the decarboxylation of glutamic acid to 4-aminobutanoic acid. The key intermediate is shown below. Draw curved arrows to show the decarboxylation step.

Question 19

Identify the correct name or abbreviation of the given nucleoside or nucleotide:

A) 2ʹ-deoxyadenosine
B) adenine
C) adenosine
D) dATP

Question 20

Shown below are the two types of base pairs in DNA, with the bases in the same relative alignments that they are in DNA.
a. Show all the relevant hydrogen bonds with dotted lines and include the unshared pairs on the acceptor atoms, within each pair.
b. Which base pair has the strongest intermolecular interaction and why?

Question 21

The nitrogen mustard mustine is toxic to cells because it reacts with two DNA bases on opposite strands of the double helix. Representing the two reacting bases of DNA as R₃N: and Rʹ₃N: show the products of the reaction of mustine with DNA in a manner that would crosslink the two DNA strands. Your mechanism should account for the very high reactivity of mustine. Show all charges and unshared pairs.

Question 22

Give the complementary sequence to the DNA strand.
5ʹ-TATGAC-3ʹ

Question 23

Give the complementary sequence to the DNA strand.
5ʹ-ACTGAC-3ʹ

Question 24

The heterocyclic base 7-aminopropargyl-7-deaza-2,6-diaminopurine has been incorporated into a short sequence of nucleotides. The structure is shown below. Compare it to the other nucleotides and determine which nucleotide base is it likely to pair with. Draw the matching nucleotide with hydrogen bonds as dotted lines.

Question 25

Omeprazole is a drug used for the treatment of acid-reflux disease. The structure is shown below. Highlight the aromatic heterocycles in the structure and name the heterocycles.