Non-covalent Interactions

Question 1

What are the three types of electrostatic interactions

Answer 1

ion-ion
ion-dipole
dipole-dipole

Question 2

Ion-ion energy?

Answer 2

100-350 kj/mol

Question 3

Ion dipole arrangement and energy?

Answer 3

Ion brings itself into line with oppositely charged dipole (50-200 kj/mol)

Question 4

What is a hydrogen bond?

Answer 4

Hydrogen atom covalently bonded to an electronegative atom which is attracted to a neighbouring dipole

Question 5

Hydrogen bond energy?

Answer 5

4-60 kj/mol

Question 6

Relative strength of hydrogen bonds?

Answer 6

Weaker than covalent bonds

If many they are highly strong due to directional nature

Question 7

What is halogen bonding?

Answer 7

Arise from appearance of sigma-hole at X. Electron density can be donated into this

Question 8

What are the types of pi-pi interactions?

Answer 8

Face to face

Face to edge

Question 9

Why can anion-pi interactions happen?

Answer 9

There is a charge difference between anion and neutral benzene

Question 10

What are the properties of dispersion forces?

Answer 10

Very general and weak (2 kJ/mol), lack directionality

Question 11

Why is steric repulsion important?

Answer 11

Achieving selectivity

Question 12

What are the stages of complexation?

Answer 12

Desolvation of anion and receptor
Binding of anion
Resolvation of host-guest complex

Question 13

What is key in complexation?

Answer 13

Thermodynamics - negative enthalpy and positive entropy is favourable, so gibbs free energy is negative and spontaneous

Question 14

What is the hydrophobic effect?

Answer 14

In a hydrophobic pocket, water molecules hydrogen bond to each other. Addition of guest leads to the release of these water molecules

Question 15

What is the enthalpy and entropy of the hydrophobic effect?

Answer 15

Enthalpy is negative - stronger non-covalent interactions have formed
Entropy is positive - release of molecules, increase in disorder