Questions about Benzene: Substituent Effects & -Cl Group

In summary, the presence of one substituent in a benzene ring affects the ease and position of any further substituent group. Halogens donate electrons by resonance and withdraw electrons by induction. However, the inductive withdrawing of chlorine is stronger than its resonance donation, making it an overall deactivating substituent for reactivity in electrophilic aromatic substitution. The ortho/para directing observed is due to the ability to draw a resonance stabilized intermediate in the mechanism. Not all ortho/para directors are as activating as a methyl group, and chlorine's electrons are donating to a degree due to delocalization.
  • #1
kanki
29
0
I have some questions here about Benzene.
So the presence of one substituent in a benzene ring will affect the ease and position of any further substituent group, such like [itex]-CH_3,NO_2,Cl[/itex].
And it's known that the Ortho,para-directing groups or electron donating groups are ring activating, consists of single bond, and will make the benzene ring easier to be attacked.
My question is, why is it that the -Cl group is electron donating? i thought it'll pull the delocalised electron in the ring and stabilise it?
 
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  • #2
kanki said:
I have some questions here about Benzene.
So the presence of one substituent in a benzene ring will affect the ease and position of any further substituent group, such like [itex]-CH_3,NO_2,Cl[/itex].
And it's known that the Ortho,para-directing groups or electron donating groups are ring activating, consists of single bond, and will make the benzene ring easier to be attacked.
My question is, why is it that the -Cl group is electron donating? i thought it'll pull the delocalised electron in the ring and stabilise it?

Halogens donate electrons by resonance, and withdraw electrons by induction through the bond. However, Cl's inductive withdrawing is stronger than its resonance donation, so it is overall a deactivating substituent for reactivity in EAS.
 
Last edited:
  • #3
So it is overall a deactivating substituent, and render the benzene ring unreactive. But why is it Ortho-para directing? Please explain...
 
  • #4
The ortho/para directing is observed because you can draw a resonance stabilized intermediate in the mechanism.
 
  • #5
And it's known that the Ortho,para-directing groups or electron donating groups are ring activating, consists of single bond, and will make the benzene ring easier to be attacked.
My question is, why is it that the -Cl group is electron donating? i thought it'll pull the delocalised electron in the ring and stabilise it?

you should re-read your text, from what I remember, not all ortho-para directors are so activating as a methyl group is for example. Chlorine's electrons are donating to a degree since it is delocalized to an extent.
 

What is benzene and what are its properties?

Benzene is a colorless, flammable liquid that is commonly used as a solvent in various industries. It is also a building block for many important chemicals. Benzene has a distinct sweet smell and is highly toxic. It is a known carcinogen and exposure to high levels of benzene can cause serious health problems.

What are substituent effects in benzene?

Substituent effects refer to the influence of different functional groups attached to a benzene ring on the reactivity and properties of the molecule. These groups can either increase or decrease the reactivity of benzene towards other molecules, depending on their electronic and steric effects.

What is the role of the -Cl group in benzene?

The -Cl group, also known as a chlorine atom, is a common substituent in benzene. It has an electron-withdrawing effect, making the benzene ring less reactive towards electrophilic substitution reactions. This group also increases the polarity of the molecule, making it more soluble in polar solvents.

What are the different types of substituent effects in benzene?

There are two main types of substituent effects in benzene: electron-donating and electron-withdrawing. Electron-donating groups, such as -CH3 and -OCH3, increase the electron density of the benzene ring and make it more reactive towards electrophilic substitution. Electron-withdrawing groups, such as -NO2 and -CN, decrease the electron density of the ring and make it less reactive.

How do substituent effects impact the stability of benzene?

Substituent effects can impact the stability of benzene by either stabilizing or destabilizing the molecule. Electron-donating groups stabilize the benzene ring, making it less likely to undergo reactions. On the other hand, electron-withdrawing groups destabilize the ring and make it more reactive. The overall stability of benzene is also influenced by the number and position of substituents on the ring.

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