benzene reactivity

[bajoneswadup]

A question from EK orgo asks about which substituent to add in order to reduce the reactivity of methyl benzoate on pg. 68.

A: NO2
B: H
C: Br
D: CH3

Answer: A


I remember in orgo that different substituents withdraw at different spots, but i didnt study this b/c benzene wont be on the mcat... Is NO2 electron withdrawing at every spot?

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[milski]

For benzene, the functional group does not change its EW/ED properties based on positions - it's always the same. What changes where other groups are being added if that group is already attached to the benzene. If I remember correctly, if there is an EW group, additions are para, if there is an ED, they are ortho/meta. ED also stimulate additions while EW will slow them down or completely prohibit them.

 

[bajoneswadup]

For benzene, the functional group does not change its EW/ED properties based on positions - it's always the same. What changes where other groups are being added if that group is already attached to the benzene. If I remember correctly, if there is an EW group, additions are para, if there is an ED, they are ortho/meta. ED also stimulate additions while EW will slow them down or completely prohibit them.

Ohh right on. NO2 is EW because of resonance with the ring in the ortho position right?

 

[Laureatebarrel]

Ohh right on. NO2 is EW because of resonance with the ring in the ortho position right?

It is electron withdrawal because the two O withdraw electron density from the N atom making the N electron positive and thus it withdraw electron density from the benzene ring. It is meta because of resonance structure. These two are different things.

 

[bajoneswadup]

It is electron withdrawal because the two O withdraw electron density from the N atom making the N electron positive and thus it withdraw electron density from the benzene ring. It is meta because of resonance structure. These two are different things.

Ohh yeah thanks.

 

[gettheleadout]

For benzene, the functional group does not change its EW/ED properties based on positions - it's always the same. What changes where other groups are being added if that group is already attached to the benzene. If I remember correctly, if there is an EW group, additions are para, if there is an ED, they are ortho/meta. ED also stimulate additions while EW will slow them down or completely prohibit them.

Electron donating groups are ortho/para directors, electron withdrawing are meta, and yes, it's due to favorable resonance contributors in electrophilic aromatic substitution.

 

[milski]

Electron donating groups are ortho/para directors, electron withdrawing are meta, and yes, it's due to favorable resonance contributors in electrophilic aromatic substitution.

Argh, I did not expect I'd screw that part. I can imagine the positions in my mind but messed up the names.

 

[goodtime]

why cant Br be the answer since it is also electron withdrawing and would make it less reactive by deactivating the ring?