Section A: Non-Covalent Interactions Flashcards Preview

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Flashcards in Section A: Non-Covalent Interactions Deck (19)
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1

Differences between covalent and non-covalent interactions

1. Covalent have a shorter range
2. Covalent are more highly directional
3. Covalent more long-lasting

2

If more than 1 bond in a molecule is polar then

The overall molecular dipole, u, must be considered

3

The overall average interaction energy between freely rotating dipolar molecules is dependant on

The distance between them : E ~ - 1/r^6
and inversely dependant on temperature

4

How are non-polar molecules held together?

The electrons in a molecule can be polarised due to the influence of a polar molecule. The permanent dipole and induced dipole can then attract.

5

Dispersion Interaction

Fluctuating electron density can cause a instantaneous dipole in non-polar molecules that induce a dipole in neighbouring molecule. These induced dipoles attract

6

Polarisability

The size of a permanent dipole

7

Dielectric constant

Measured experimental values that determine how well a material stores electrical energy when exposed to an electric field -> property of the bulk substance

8

Generally more polar molecules have

Higher dielectric constants

9

When an ion is surrounded by polar molecules,

Many of their dipoles align in the field of the ion which lowers self-energy of ion

10

Why are H-bonds generally short ranged?

The formation of H bonds involves overlap of AO's

11

Why are the properties of water anomalous?

Each water molecule can form up to 4 H-bonds with other water molecules, 2 as acceptors 2 as donors

12

The Grotthuss Mechanism

Conduction of H+ through water is an order of magnitude faster than conduction of similarly charged ions. This is because H bonds can become covalent bonds (visa versa) allowing transfer of charge from one location to another without diffusion of atoms.

13

In TLC, the mobile phase is driven by

Capillary forces

14

In TLC, affinity to stationary phase is dependent on

Strength of non-covalent interactions

15

Why do systems with H-bonds have high entropy?

There are many ways of arranging the H bonding network, each of the same energy

16

Hydrophobic molecules

Can't form H-bonds -> reduces entropy

17

The hydrophobic effect

Clustering of non-polar molecules due to entropically unfavourable interaction with water

18

Amphiphile

Both hydrophobic and hydrophilic e.g. lipids

19

Amphiphile self-assembly

Amphiphile's self assemble in order to minimise the hydrophobic effect