Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

S2 Case 3 - asthma & COPD > Heteroaromatic Chemistry > Flashcards

Heteroaromatic Chemistry Flashcards

(67 cards)

Start Studying
1
Q

Why is benzene stable?

A

Due to delocalisation of e-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

When does aromaticity occur?

A

Compound has uninterrupted cyclic cloud of p e- above + below plane of planar molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What should the e- cloud contain in aromaticity?

A

Odd number of pairs of p e-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is Huckel’s rule?

A

For planar, cyclic compound to be aromatic must contain uninterrupted p cloud with 4n + 2 e-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are examples of heterocycles in nature?

A

DNA
Haemoglobin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is a heterocycle?

A

Any ring containing at least 1 heteroatom (NOT C)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are some heteroatoms?

A

N
O
S

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What set of hybrid orbitals are in benzene?

A

sp2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What do the p-orbitals in benzene generate?

A

Pi network

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How is the pi system formed?

A

Each p e- is delocalised over 6 Cs creating pi system above + below plane of hexagon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is pyridine?

A

Derived from benzene
CH is replaced with a sp2 hybridised N atom

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why is there a permanent dipole towards N in pyridine?

A

Inductive effects + resonance work in the same direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does the N do in pyridine?

A

Pull e- towards itself
= more electronegative than C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Where are pyridine’s partial positive charges?

A

Alpha position
Gamma position

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the alpha positions?

A

2 + 6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the gamma positions?

A

4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is pyridine termed as?

A

“Electron poor”
OR
Pi deficient system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What does the electronegative N in pyridine cause?

A

Inductive polarisation = additional structures = resonance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the pKa of pyridine?

A

5.2 = WB

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What does in the N in pyridine make it?

A

Basic
NOT the reason for it being aromatic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Can pyridine undergo electrophilic aromatic substitution?

A

YES, BUT harder than with benzene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are the physiochemical properties of pyridine?

A

Soluble in H2O
H bonding possible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the N in pyridine?

A

HBA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What are most drugs absorbed by?

A

Passive diffusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What happens if a drug has a basic centre?
Make a salt = more soluble than parent compound
26
Describe H2O solubility of drug absorption
Almost all drugs are H2O soluble to undergo passive diffusion to some extent
27
Describe lipid solubility of drug absorption
Passive diffusion depends mainly on lipid solubility
28
Why must molecule be unionised?
As only unionised form diffuses
29
What does ionisation depend on?
Depends on pKa of drug + pH of solution
30
What do EDGs do?
Increase the HDA ability + pKa value (= increase basicity)
31
Because the N is NOT part of the pi system what can it do?
Behave as a nucleophile
32
Describe pyridine N-oxides
More polar than pyridine Made with per-oxy acid or hydrogen peroxide
33
What does N-oxide promote?
Both electrophilic + nucleophilic substitution reactions
34
Describe nucleophilic substitution in pyridine
Occur more readily than in benzene Positions 2 + 4
35
What do EDGs facilitate?
Reactions via EsAR
36
What do EWGs facilitate?
Reactions via SnAR
37
Describe amino pyridines
More basic Resonance between 2 + 4 amino isomers
38
What do 2 + 4 amino isomers form?
Mono-salt
39
What do 3-isomer amino form?
Double salt
40
What are all 3 hydroxy-pyridines subject to?
Tautomerism involving H exchange = pyridones
41
What positions do pyridones exclusively exist in?
2 + 4
42
In 6 membered rings, where does electrophilic substitution occur?
On the benzene ring
43
What happens if you add 2nd N?
Decrease pKa = decrease basicity
44
Describe other N containing 6-membered rings
Weaker bases than pyridine All aromatic Less reactive
45
What does acidic sulphonamide group do?
Give up H+ = conjugate base has resonance
46
What are the common 5-membered heterocycles in single system rings?
Pyrrole - NH Furan - O Imidazole - NNH Thiophene - S
47
What are some common 5-membered heterocycles in fused ring systems?
Indole - NH Benzimidazole - NNH Benzothiophene - S Benzofuran - O
48
What do 5-membered rings not fulfil + why?
Huckel criteria = each molecule only appears to have 4 pi-e- = 1 L.P used to make system
49
Are 5-membered rings aromatic?
YES
50
Describe pyrrole L.P
Delocalised = NOT available for donation to E+
51
What is the pKa of pyrrole?
-4 = non-basic
52
What are furan + thiophene?
Analogous in structure to pyrrole
53
What are difference between furan & thiophene compared to pyrrole?
Heteroatoms (O + S) have 2 L.Ps of e-
54
Describe the L.Ps in furan + thiophene
1 L.P delocalised = aromaticity 2nd located in sp2 orbital
55
Describe order of electronegativity in S, O + N
S < N < O
56
Describe the order of aromaticity in pyrrole, thiophene + furan
Thiophene > pyrrole > furan
57
What is the reactivity of pyrrole, furan + thiophene dominated by?
Their readiness to undergo electrophilic substitution
58
Describe the order of reactivity in pyrrole, thiophene + furan?
Pyrrole > furan > thiophene
59
Where does electrophilic attack mostly occur in pyrrole, thiophene + furan?
2-position
60
Does pyrrole, thiophene + furan all undergo EAS?
YES
61
Describe oxazole
5-membered ring system N + O Heterocycle is aromatic WB = pKa = 0.8
62
Describe imidazole
5-membered ring system NN - 1 like pyridine, 1 like pyrrole pKa = 7 N = sp2
63
What is important about imidazole?
Soluble in H2O = forms extensive H bonding networks
64
Describe tautomerism in imidazole
Rapid transfer of H from one nitrogen to the other 2 tautomers in inseparable eqm mixture
65
What is it called when H-atoms change position in heterocyclic systems?
Annular tautomerisations
66
What are bicyclic heterocycles?
Indoles = benzo-fused pyrroles
67
Describe indole reactivity
Reactive pyrrole + unreactive benzene

S2 Case 3 - asthma & COPD (25 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions