Supramolecular Chemistry CH30211

Question 1

Which nucleotide bases join more strongly?

Answer 1

Guanosine and Cytosine, 3 hydrogen bonds

Question 2

Guanosine forms a tetraplex through which interactions?

Answer 2

Hydrogen bonding, then pi stacking in a parallel and antiparallel manner

Question 3

How can a cation be separated from solution?

Answer 3

With a crown ether, binding constant for substrates varies with ring size (e.g. [18]crown-6 strong for potassium)

Question 4

What is supramolecular chemistry? Why is it important?

Answer 4

The chemistry of intramolecular bonds, important for describing the behaviour and properties of a system

Question 5

How can a supramolecular system develop?

Answer 5

Host-guest complex or Self assembled aggregates (solid/solution) or latticed complexes (solid)

Question 6

What is a host-guest interaction?

Answer 6

The binding of a small molecule to a larger molecules binding pocket

Question 7

What is the lock and key concept?

Answer 7

That guest is geometrically, interactionally and has shape complementarity to the host, allows discrimination between interactions

Question 8

How is the lock and key argument flawed?

Answer 8

It is misleadingly rigid, underestimating the effects of entropy

Question 9

What is the induced fit theory?

Answer 9

Guest triggers change in host. Allows host to interact with different (similar) guest

Question 10

What are the key features to an ion-ion interaction?

Answer 10

Very Strong
Attractive or repulsive
Non-directional
Long range
Highly dependent on dielectric constant of the medium

Question 11

What are the key features to an ion-dipole interaction?

Answer 11

Weak
Attractive or repulsive
Directional
Medium range
Highly dependent on dielectric constant of the medium

Question 12

What are the key feature to a dipole-dipole interaction?

Answer 12

Weak
Directional
Highly dependent on the dielectric constant of the medium

Has been observed in solid-state carbonyls

Question 13

What are the key features to a cation-pi interaction?

Answer 13

A special subset of dipole-dipole interactions, with a diverse energetic landscape

Question 14

What are the key features to an anion-pi/anion-pi* interaction?

Answer 14

Very weak

Only in electron-deficient aromatic systems

Question 15

What are the key features to an pi-pi interaction?

Answer 15

Weak
Directional
Heavily dependent on the dielectric constant of the medium

Heavily influenced by the nature of the pi-system

Question 16

What are the key features to van der Waals interactions?

Answer 16

Very weak
Non-directional
Dependent on polarizability of the molecule

Minimises void spaces in crystals

Question 17

What are the key features to closed shell interactions?

Answer 17

Very weak
Heavy metal-metal interactions
Halogen bonds (polarisable halogens and electronegative atoms)

Question 18

What are the key features to a hydrogen bond interaction?

Answer 18

Direction interactions with a diverse energy landscape
Attractive and repulsive
Primary and secondary
A special subset of dipole interactions
Ubiquitous in nature, highly dependent on the dielectric constant of the medium

Question 19

What are the different geometries of hydrogen bonding which may occur?

Answer 19

Linear
Bent
Donating bifurcated (two acceptors)
Accepting bifurcated (two H on donor)
Trifurcated (three acceptors)
Three centre bifurcated (two H on donor, to three acceptors)

Question 20

What are strong and weak hydrogen bonds similar to?

Answer 20

Strong hydrogen bonds have near covalent character

Weak hydrogen bonds have near van der Waals character

Question 21

What is the solvophobic effect?

Answer 21

The tendency of solute particles to cluster as the attractive interaction between solvent particles is strengthened

Question 22

What are the key features to the solvophobic effect?

Answer 22

Very weak
Ubiquitous
All molecules are solvated at all times
Has enthalpic and entropic factors

Question 23

What is the effect of the solvophobic effect?

Answer 23

Has enthalpic and entropic factors:

For guest and host to interact, solvation must be overcome

Question 24

What is enthalpically (un)favourable in guest-host interaction

Answer 24

Unfavoured: Desolvation of host/guest and host rearrangement
Favoured: Complexation and solvation of host

Question 25

What is entropically (un)favourable in the guest-host interaction?

Answer 25

Unfavoured: solvation of complex
Favoured: desolvation of host/guest

Question 26

Why is choosing the correct solvent desirable?

Answer 26

In some solvents, different solutes will interact favourable: in other solutes the solvent-solute interaction will dominate preventing the reaction

Question 27

Give an example of an ion-ion interaction

Answer 27

Negative to positive ion

Question 28

Give an example of an ion-dipole interaction

Answer 28

Carbonyl to positive ion

Question 29

Give an example of a dipole-dipole interaction

Answer 29

Carbonyl oxygen, to carbonyl carbon

Question 30

Give an example of a cation-pi interaction

Answer 30

Positive ion to an aromatic ring, e.g. artificial ion channels

Question 31

Give an example of an anion-pi interaction

Answer 31

e.g. artificial ion channels

Question 32

Give an example of a pi-pi interaction

Answer 32

Face-to-face and edge-to-face aromatics.

Repulsion will occur if stacked directly on top

Question 33

Give an example of hydrogen bonding

Answer 33

Water to water.

AAA opposite DDD will give primary and secondary attractive hydrogen bonding

ADA to DAD will give primary attractive and secondary repulsive hydrogen bonding