Arenes

Question 1

carbon carbon bond length in benzene

Answer 1

intermediate between c-c and c=c bond length
indicates the bond has partial double bond character
electron density is evenly distributed and delocalisation of electrons is present

Question 2

why does benzene undergo electrophilic subsituition instead of addition

Answer 2

electrophilic addition would disrupt the resonance stabilisation that is associated with delocalisation of the 6 pi electrons in benzene
electrophilic subsitution would only temporarily disrupt the resonance stabilisation and would be restored in the product

Question 3

why does benzene attract nucleophiles

Answer 3

it is electron rich from the presence of 6 pi electrons

Question 4

why is the electrophilic attack step a slow step

Answer 4

it involves disrupting the delocalised pi electron cloud and losing the extra resonance stabilisation

Question 5

bronsted lowry acid

Answer 5

proton donor
has an empty orbital to accept electrons

Question 6

bronsted lowry base

Answer 6

proton acceptor
has a lone pair of electrons

Question 7

lewis acid

Answer 7

electron pair acceptor

Question 8

lewis base

Answer 8

electron pair donor

Question 9

why does halogenation require a lewis acid catalysts

Answer 9

stronger electrophile required to disrupt extra stability associated with aromacity of benzene

Question 10

why must halogenation take place in anhydrous conditions

Answer 10

alcl3 catalyst reacts readily with water through hydrolysis and after hydrolysis it cannot act as a lewis acid

Question 11

effect of deactivating group

Answer 11

subsituent makes new compound less reactive than benzene

Question 12

how is deactivation acheived

Answer 12

by electron withdrawing groups
decrease electron density in benzene ring, intensifies positive charge of carbocation intermediate, destabilises carbocation, makes ring less susceptibe to attack

Question 13

effect of activating group

Answer 13

subsituent makes new compound more reactive than benzene

Question 14

how is activation acheived

Answer 14

by electron donating groups
increases electron density in benzene ring, disperses positive charge of carbocation intermediate, stabilises carbocation, makes ring more susceptibe to attack

Question 15

electron donating by inductive effect

Answer 15

groups with sp3 carbon
have lower s character, electrons less tightly held, more easily fonated through sigma bond to benzene ring

Question 16

electron donating by resonance effect

Answer 16

subsituents with lone pair of electrons
lone pair will be held in unhybridised p orbitals, delocalises into ring

Question 17

electron withdrawing by inductive effect

Answer 17

subsituent/atom more electronegative than carbon
pulls electrons closer to themselves, pull electron density away from C of benzene through sigma bond

Question 18

electron withdrawing by resonance effect

Answer 18

atom directly attached to C of benzene ring is doubly/triply bond to a more electronegative atom
pi electrons of benzene ring can be delocalised onto subsituent as it pulls elecctrons away from benzene ring towards itself

Question 19

what is overall effect exerted by chlorine as a subsituent

Answer 19

electron withdrawing inductive effect
is in period 3, has more diffuse p orbitals, less effective side on overlap with p orbitals of benzene ring

Question 20

conditions for oxidation of alkyl side chain of methylbenzene

Answer 20

only alkylbenzenes with a hydrogen/oxygen atom directly bonded to the carbon atom that is bonded to benzene ring can undergo oxidation