Module 4, Lecture 9

Question 1

What are aromatic compounds?

Answer 1

Molecules with rings of atoms which are joined via alternating double and single bonds and, specifically, have either 6 or 10 electrons that are not in sigma bonds, have unusual stability and unusual reactivity

Question 2

How do the properties of nitrogen atoms change in aromatic systems?

Answer 2

Aromatic ring compounds containing nitrogen instead of carbon are called heterocyclic compounds. The aromatic nature of the molecule can affect the acid base chemistry of the nitrogen.

Question 3

Pyradine?

Answer 3

has 6 electrons in the three pi bonds so is an aromatic

compound. However, the nitrogen still has its lone pair, so it is still able to act as a base

Question 4

Pyrrole?

Answer 4

e has 4 electrons in the two pi bonds, but if it adds the two electrons in the nitrogen’s lone pair, then it gets the six it needs to be aromatic. When it does this, the nitrogen is no longer basic.

Question 5

Imidazole?

Answer 5

has two nitrogen atoms in the ring, but again only two pi
bonds. So the lone pair of one of the nitrogen’s is taken to make the 6 electrons from the aromatic system (meaning that this nitrogen is not basic) but the other nitrogen keeps its lone pair and so is basic.

Question 6

Fused Systems - Indole?

Answer 6

e has two rings which share two atoms (a fused system). In this case the nitrogen lone pair is acquired to make a 10-electron aromatic system.

Question 7

Examples of aromatic systems in biological molecules?

Answer 7

‘Bases’ in DNA and RNA are based on purine and pyrimidine groups.
Nucleosides – the bases joined to a ribose sugar group
Nucleotides – the nucleosides joined to a phosphate group – the building blocks of DNA and RNA

Question 8

Function of ATP?

Answer 8

ATP acts by hydrolysis of one of the phosphate bonds – ATP à ADP. Negative charges on the phosphates repel nucleophiles, so reaction is catalysed by an enzyme and is facilitated by Mg2+.

Question 9

DNA Vs RNA structure?

Answer 9

DNA is much more stable than RNA – again it is the phosphate bond which breaks and the OH group on C2’ acts as an internal nucleophile to facilitate bond breakage in RNA (DNA does not have an OH group at this position.