Mechanisms

Question 1

What must a leaving group be able to do?

Answer 1

Must be able to accept both electrons in the bond that breaks.
Therefore, a leaving group is a species that will leave if given electrons.

Question 2

Examples of leaving groups:

Answer 2

Not including C
C-Cl, C-OH, C-OCH3, C-Br, C-OH2, C-OHCH3, C-I

Question 3

What is the order of carbocation stability?

Answer 3

3>2>1>0
The more carbon atoms attached to the carbocation centre, the more substituted the carbocation.

Question 4

What’s a methyl carbocation?

Answer 4

Carbon atom not connected to any carbon, only 3 hydrogens.

Question 5

What are electron-poor substrates?

Answer 5

Can accept an electron pair to form a new bond.
They are attached by nucleophiles.
Has a partial or full positive charge.

Question 6

What are electron-rich substrates?

Answer 6

Act as electron diners and attack electrophiles.
Double bonds are electron rich and are electron rich.

Question 7

Key info on Aromatic rings

Answer 7

More stable than expected- double bonds in the ring are much less reactive than non-aromatic double bonds.
Due to the electrons being delocalised over the ring.
In order to react, this aromatic stabilisation must be temporarily or permanently destroyed.
Therefore, aromatic rings resist addition reactions.
Substitution reactions are possible if the conditions are extreme enough.

Question 8

What is an electrophilic reagent?

Answer 8

An electron-poor species that can affect an electron pair to form a new bond.

Question 9

What are the 3 types of electrophilic reagents?

Answer 9

1. Positively charged
2. Have a small permanent partial charge
3. Polarisable - so that a nearby electron-rich species can induce a temporary partial positive charge.

Question 10

What is a base?

Answer 10

An electron-rich species that can abstract (remove) a hydrogen atom.
This is known as having an affinity for H atoms.

Question 11

What is a nucleophile?

Answer 11

An electron-rich species that donates electrons to an electron-poor atom, forming a covalent bond.

Question 12

Comparing O- and N- based nucleophiles

Answer 12

1. Negatively-charged nucleophiles are stronger than uncharged nucleophiles.
2. If the charges are the same, N- based nucleophiles are stronger than O- based nucleophiles.

Question 13

What does increasing the steric hindrance of groups next to the nucleophiles atom do?

Answer 13

1. Decreases the strength of the nucleophile.
2. But, has very little effect on the base strength

Question 14

How to generate radicals?

Answer 14

1. UV light
2. Heating a radical initiator

Question 15

Describe the 3 stages of a radical reaction.

Answer 15

1. Initiation - radicals are generated from non-radical starting materials. The number of radicals increases due to this stage.
2. Propagation - radicals react with non-radicals. The number of radicals is not changed by this stage.
3. Termination - 2 radicals react to form non-radical products. The number of radicals decreases due to this stage.

Question 16

What are the 3 categories of solvents?

Answer 16

1. Non-polar - has no (or small) overall dipole movement.
2. Polar-protic - overall dipole movement. Has N-H, O-H or F-H bond. (Able to form hydrogen bonds to species).
3. Polar-aprotic - overall dipole movement. Doesn’t have a N-H, O-H or F-H bond. (Cannot form hydrogen bonds to other species).