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F324 January 2012 Paracetamol Benzene + Bromine help [PLEASE HELP]

The question and corresponding answer is given.

Why are there two bromines rather than just one?

I'm confused why the bromine atoms are placed on either side of the benzene molecule.

Thanks.
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Original post by nwmyname
The question and corresponding answer is given.

Why are there two bromines rather than just one?

I'm confused why the bromine atoms are placed on either side of the benzene molecule.

Thanks.


The -OH group attached to the benzene ring is 2,4,6 directing and activating. Hence the tendency would be for triple substitution, but in this case the 4- position is already taken up so substitution happens at only the 2 and 6 positions of the ring.
Reply 2
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nwmyname
OP
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Original post by charco
The -OH group attached to the benzene ring is 2,4,6 directing and activating. Hence the tendency would be for triple substitution, but in this case the 4- position is already taken up so substitution happens at only the 2 and 6 positions of the ring.


Got you!
Thanks.
Reply 3
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nwmyname
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Original post by charco
The -OH group attached to the benzene ring is 2,4,6 directing and activating. Hence the tendency would be for triple substitution, but in this case the 4- position is already taken up so substitution happens at only the 2 and 6 positions of the ring.


Hold on
the Br groups are only at the 2 and the 5 positions.
how is this the case.
It is not 6.

No I think because the OH is 2 and 4 activating but so is the -NHR group which also does the same job.

The Br is in position 2 from the -OH and so the -NHR group is in 4 if seen anticlockwise (Down then up)

Please help!
(edited 7 years ago)
Reply 4
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alow
19
Original post by nwmyname
Hold on
the Br groups are only at the 2 and the 5 positions.
how is this the case.
It is not 6.

No I think because the OH is 2 and 4 activating but so is the -NHR group which also does the same job.

The Br is in position 2 from the -OH and so the -NHR group is in 4 if seen anticlockwise (Down then up)

Please help!


The Brs are at the 2 and 6 positions, with the -OH attached at 1. Count again.

It's an -NHCOR group which is o/p directing but not as strongly as -OH (think of this in terms of how much electron density is donated to the π system).
(edited 7 years ago)
Reply 5
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nwmyname
OP
13
Original post by alow
The Brs are at the 2 and 6 positions, with the -OH attached at 1. Count again.

It's an -NHCOR group which is o/p directing but not as strongly as -OH (think of this in terms of how much electron density is donated to the π system).


Got it.
Now it makes sense perfectly.
Thanks very much :smile:

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