Topic 20
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What are nucleophiles?
Electron pair donors that are attracted to regions of positive charge
What are electrophiles?
Electron pair acceptors that are attracted to regions of negative charge
Why is OH- a better nucleophile than H20
Because OH- has a negative charge while water only has a dipole so is more strongly attracted to the carbon atom
Describe nucleophilic substitution
Replacement of an atom via a nucleophile
What kind of halogenoalkanes undergo SN1?
Tertiary and secondary
What kind of halogenoalkanes undergo SN2?
Primary
What is the rate expression for SN1?
Rate = K [ halogenoalkane]
What is the equation for the formation of NO2 nucleophile?
HNO3+ 2H2SO4 — NO2+ + 2HSO4- + H30+
What kind of reaction is the nitration of benzene?
Electrophillic substitution
What is the overall equation for nitration of benzene?
C6H6+ HNO3— C6HNO2 + H20
What is the rate expression for SN2?
Rate = K [Halogenoalkane][nucleophile]
What type of solvent is favoured by SN1?
Polar protic solvents which have hydrogen bonds
What type of solvent is favoured by SN2?
Polar aprotic solvents which are unable to form hydrogen bonds
What shape is the SN1 carbocation?
Trigonal plannar
What type of mixture does SN1 produce?
Racemic mixture which has no effect on the plane of polarised light
Why do alkenes undergo electrophilic addition?
• carbon to carbon double bond • high electron density • attracted to electrophiles
What is isomerism?
When they have the same molecular formula but different arrangements in space
What are the two types of isomerism ?
Configurational ( alkenes) and conformation ( alkanes)
What is needed for cis- trans configurational isomerism?
• 2 different groups on each carbon atom • restricted rotation around the carbon to carbon double bond • alkenes or cyclo alkanes
What is needed for E/Z isomerism?
• up to 4 constituent elements bonded to the two carbon atoms
How do you know if it is a Z isomer?
The highest priority groups are on the same side
How do you know if it is a E isomer?
The highest priority groups would be on different sides
What is nitrobenzene reacted with to reduce it?
Tn and Hcl
What is produced during stage 1 of the reduction of benzene?
Phenyl ammonium ion