Electrophilic Substitution Flashcards
what are the catalysts used in step 1 of electrophilic substitution called?
- halogen carriers
- FeCl3 or AlCl3
- FeBr3 or AlBr3
what always happens in step 3 of electrophillic substitution?
the catalyst is regenerated
why is step 1 of electrophillic substitution done?
make the electrophile very reactive
what is the reaction of benzene with haloalkanes called?
friedel-craft alkylation
what is the reaction of benzene with acyl chlorides called?
friedel-craft acylation
compare the reactivity of alkenes and benzene.
alkenes react with bromine much more readily than benzene does
explain cyclohexene(alkenes) and bromine water reaction.
- the pi bond in cyclohexene contains localised electrons which is a region of high electron density
- the electrons in the pi bond repel the electrons in the Br-Br bond and polarises the Br2 molecule
- the pair of electrons in the pi bond are now attracted to the slightly positive Br atom, causing the double bond to break
what is the process of the reaction of cyclohexene and bromine water?
- a new bond forms between the carbon atom and bromine atom, forming a carbocation on the other carbon of the alkene
- as this happens, the Br-Br sigma bond breaks, forming a bromine ion
- the Br- is attracted to the intermediate carbocation, forming a covalent bond
explain benzene and bromine water reaction.
- benzene has delocalised electrons which spread over all 6 carbons in the ring, creating a lower electron density than in an alkene
- when a non-polar molecule (bromine) approaches there is insufficient pi electron density above or below any 2 carbon atoms to polarise the Br-Br bond
- make benzene resistant to reactions with non-polar halogens
what is needed for the reaction of bromine and benzene?
a halogen carrier to generate a more powerful electrophile
what is an electrophile?
an electron pair acceptor
