arenes

Question 1

implications of pi e- cloud delocalisation

Answer 1

1. cause all C-C bond lengths to be equal
2. creates a planar m, regular hexagonal shape

&

1. prevents benzene from undergoing any of the typical addition reactions that alkene show

Question 2

why does benzene undergoes E.S & not E.A?

Answer 2

1. Pi e- cloud attracts E+
2. E.A destroys the delocalised pi e- cloud which requires a sig. amt. of energy
3. highly unfavourable
4. benzene preferentially undergoes E.S which preserves its aromaticity

Question 3

explain substituent effect on reactivity of benzene ring towards E.S

Answer 3

1. EWG via inductive effect reduces electrophilicity
2. alkyl group inductively donates e- density into benzene ring, increasing electrophilicity
3. groups w/ LP of e- in p orbital directly joined to benzene ring can donate LP into benzene ring via delocalisation which increases e- density