Question 1

Identify the missing reagent(s) for the transformation:

Accepted Answer

The pyridine ring can undergo nucleophilic aromatic substitution. An organolithium reagent, such as PhLi, will be used to form a carbon-carbon bond. An aqueous workup gives the desired substituted pyridine. The byproduct of the reaction is LiH.

Question 2

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

Accepted Answer

Start by adding lone pairs to each heteroatom.

Compound A is aromatic, as the nitrogen contributes two electrons to the pi electron system, giving an overall count of six pi electrons. Compound B is nonaromatic, as it does not have a p orbital on the nitrogen and is sp³ hybridized. Compound C is aromatic, as the lone pairs on each nitrogen are located on an sp² orbital and not part of the pi electron system. Compound D is aromatic, as one of the lone pairs on the oxygen contributes to the pi electron system of the ring, giving an overall count of six pi electrons.

Question 3

Outline a synthesis for the transformation:

Accepted Answer

The first step is an electrophilic aromatic substitution to add the acetyl group. The second step is a Grignard addition to the ketone to give the tertiary alcohol.
​

Question 4

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.

Accepted Answer

The pyridine ring in pyridoxal phosphate

Question 5

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?

Accepted Answer

a. Adenine and thymine form tw

Question 6

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

Accepted Answer

The answer of Draw a structure for each of the...

Question 7

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

Accepted Answer

The answer of Draw a structure for each of the...

Question 8

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

Accepted Answer

The letters T and A refer to thymine and

Question 9

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

Accepted Answer

The lone pair in the five-membered heter

Question 10

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

Accepted Answer

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

Question 11

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

Accepted Answer

The reaction is a nucleophilic aromatic

Question 12

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

Accepted Answer

The lone pair of nitrogen is p

Question 13

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.

Accepted Answer

The lone pair on the nitrogen bonded to

Question 14

Name the heterocycle.

Accepted Answer

The hetero

Question 15

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

Accepted Answer

Draw the carbocation intermediate formed

Question 16

Name the heterocycle.

Accepted Answer

The hetero

Question 17

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.

Accepted Answer

The purine is similar to the t

Question 18

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.