- Acetamido group is electron donationg and so it is ring
activating.
- Acetamido group is ortho or para directing.
- There is pumped electron density by acetamido group attached to
the benzene ring.
- This electron density is accumulated at ortho and para
positions.
- Now acetamido group is bulky it obstructs the incoming
electrophile attacking at ortho positions.
- para position in acetamidobenzene (acetanilide) is more free
comparatively, to be attacked by electrophile in electrophylic
substitution of acetamido benzene.
- if the incoming or attacking group is also bulkier then the
electrophile without any hesitations attacks the para positopns.
only
- So steric hidrance is the main role player in deciding the para
postions in acetamido benzene and electrophylic substution occurs
mainly at para positions comparitive to ortho position is
acetamidobenzene.
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- amino group and acetamido group both are electron donating and
ring activating groups.
- Amino group is more strong electron donating group than
acetamido group.
- so the rate of electrophylic substituion is slower in acetamido
benzene than aniline.
- The electron density on nitrogen atom is dragged by the more
electronegative atom oxygen in R-(c=o)-NH (acetamido group).Rimg
activation becomes slow in acetanilide.Also incoming eletrophile is
hindered by bulkier acetamido group
- By the time electrophile orients itself to the attacking site
in acetanillide , the reaction completes in aniline.
Aatawlide