nucleophilic substitution

what is a nucleophile

a region of high electron densisty,from a lone pair or from negative charge

what is an electrophile

a region of low electron density, for example an atom next to an electronegative atom or a carbocation would be electron deficient

what makes a good leaving group

its able to stabilise a negative charge so its is more likely to be formed

explain the SN2 mechanism

• substitution nucleophilic bimolecular

• the nucleophile attacks ( 180 attack ) the electrophile to make a bond and then a bond is broken

• a high energy transition state is made which shows the nucleophile joining and the leaving group leaving

• the product is formed containing the nucleophile is made which has a stereochemical centre that is inverted

what things are required/ encourgae SN2 

• a good nucleophile-one that is able to displace the leaving group 

• primary substrates 

explain the SN1 mechanism 

• substitution nucleophilic unimolecular 

• due to steric hinderance initially the nucleophile cant attack 

• first the leaving group needs to leave 

• once its left the nucleophile is able to attack the carbocation produced - it has an equal chance of attaching at either position racemic 

what are the features of a SN1 reaction and what can cause it to occur

• only one molecule is involved at the start

• the first step ( waiting for the leaving group to leave ) is the rate determining step and the slowest

what causes it:

• weak nucleophiles 

• large nucleophiles 

• stabilised carbocation

• a very good leaving group  

explain E1

• first the the leaving group leaves in the slowest rate determining step

• this forms a carbocation intermediate to be formed which the base can take a proton from to form a molecule with a double bond

explain E2

• elimination bimolecular

• the base attacks the proton ( attacks the proton which allows maximum orbital overlap ) making a bond and a bond between the leaving group is broken

• it goes through the transition state

• finally forms the molecule with the double bond