Heteroaromatic Chemistry 1 and 2

Question 1

Why does benzene have equal energy canonical forms?

Answer 1

because it has an uninterrupted cyclic cloud of p electrons above and below the plane of the planar molecule and this electron cloud contains an odd number of pairs of p electrons

Question 2

what is Hückel’s rule?

Answer 2

For a planar, cyclic compound to be aromatic, it must contain an uninterrupted p cloud with (4n + 2) p electrons, where n is any whole number.

Question 3

what is a heterocycle?

Answer 3

any ring containing at least one heteroatom (aka not C). Usually N, O or S replace the C in the ring.

Question 4

what is a pyridine?

Answer 4

a benzene ring with one of the carbon atoms replaced with a nitrogen atom.

Question 5

what type of system is pyridine termed as?

Answer 5

an electron poor/ pi-deficient system

Question 6

are pyridines acidic or basic?

Answer 6

basic

Question 7

where do electrophiles attack in a pyridine?

Answer 7

the lone pair of electron on the nitrogen

Question 8

which undergoes electrophilic aromatic substitution more readily, benzene or pyridines?

Answer 8

benzene

Question 9

where do electrophiles attack the pyridine?

Answer 9

in the meta position

Question 10

what are the physiochemical properties of pyridines?

Answer 10

1. soluble in water
2. can form H bonds
3. has a pKa of 5.20

Question 11

What type of drugs will diffuse across the cell membrane?

Answer 11

lipid soluble drugs

Question 12

What are the essential factors for drug absorption?

Answer 12

1. water solubility (for passive diffusion to some extent)
2. Lipid solubility (for diffusion through cell membranes)
3. Unionised drug (only unionised form can diffuse)
4. molecular size
5. surface area of absorption site
6. concentration at absorption site