Preferential meta para and ortho positions substitutions.

  • Thread starter Kushal
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In summary, the conversation discusses the potential substitution of a bromine atom when adding aqueous bromine to 4 methyl phenyl amine and 3 methyl phenol. The reaction is electrophilic substitution and the outcome depends on which activating group, methyl or amine, is stronger. Both groups are ortho and para directing and the effect of resonance donation is typically stronger than hyperconjugation. The question is asked from a second semester organic chemistry course and the concepts of resonance and activating/deactivating groups are necessary to understand the problem. The conversation ends with the suggestion to refer to a textbook or the internet for information on which group is a stronger activator.
  • #1
Kushal
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1

Homework Statement



If i have 4 methyl phenyl amine and i add aqueous bromine. where will the bromine atom substitute.

And would adding aqueous bromine to 3 methyl phenol have a different reaction/observation.

Homework Equations


The Attempt at a Solution



I think it will depend on which is a stronger activating group. the methyl or amine group.

both organic compounds react similarly with bromine, with the same observations.
Discharge of reddish brown colour + acidic fumes of HBr.

the reaction is electrophilic substitution in both.
 
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  • #2
Kushal said:
I think it will depend on which is a stronger activating group. the methyl or amine group.
Exactly. There are two competing activating groups; therefore the addition will most likely occur at the position that is favored by the most activating group. So which one is stronger? What kind of director is it?
 
  • #3
both methyl and amine groups are ortho and para directing because they are activating groups.

but i don't know which one is stronger.
 
  • #4
this is something you could find pretty easily in your orgo text, but resonance donation typically has a stronger directing effect than hyperconjugation.
 
  • #5
what you saying is advanced chemistry for me! we don't do resonance.

but can you tell me which groups are stronger and which are weaker?!

thnks
 
  • #6
You are asking a question from a second semester organic chemistry course. It's silly to even think about this question if you haven't already covered the prerequisite concepts to understand it. In order to understand a substituents directing effects you absolutely need to think about resonance, otherwise you are just blindly memorizing.

What year are you in school?
 
  • #7
i'm in last year of high school. we do cambridge A levels. sometimes they give organic questions with different activating groups attached to a benzene ring and where a slight knowledge of which activating/deactivating group is stronger and weaker might be very helpful, at least to understand the problem.

we also study many reactions without getting into the mechanisms: elimination rxns,...
 
  • #8
It's quite strange that they would teach you like that without covering the concepts that make it understandable... anyway, you can easily find in a textbook, or on the internet, which group is a stronger activator.
 
  • #9
alright...thnks:)
 

1. What is the difference between meta, para, and ortho positions?

The meta, para, and ortho positions refer to the relative positions of substituent groups on a benzene ring. In the meta position, the substituent is located on the third carbon atom, counting from the carbon atom directly across from the substituent. In the para position, the substituent is located on the fourth carbon atom, counting from the carbon atom directly across from the substituent. In the ortho position, the substituent is located on the adjacent carbon atoms.

2. How do substituents preferentially occupy the meta, para, and ortho positions?

The preference for substituents to occupy the meta, para, or ortho positions is determined by steric and electronic effects. Steric effects refer to the physical size and shape of the substituent, while electronic effects refer to the electronic properties of the substituent. Generally, bulky substituents prefer to occupy the meta position due to steric hindrance, while electron-donating substituents prefer to occupy the ortho and para positions due to electronic effects.

3. What is the significance of preferential meta, para, and ortho positions substitutions?

The preferential occupation of the meta, para, and ortho positions can have a significant impact on the reactivity and properties of the substituted benzene ring. For example, meta-substituted compounds may have different physical and chemical properties compared to para-substituted compounds due to the different spatial arrangements of the substituents. This can also affect the reactivity of the compounds towards other chemical reactions.

4. What factors influence the preference for meta, para, and ortho positions substitutions?

As mentioned before, steric and electronic effects play a major role in determining the preference for meta, para, and ortho positions substitutions. However, other factors such as the nature of the substituent, the reaction conditions, and the presence of other functional groups can also influence the preference for substitution at a particular position.

5. Can substituents occupy multiple positions on a benzene ring?

Yes, it is possible for substituents to occupy multiple positions on a benzene ring. In fact, some reactions can result in multiple substitution events, leading to compounds with multiple substituents at various positions on the benzene ring. However, the preference for specific positions may still be observed in these compounds based on the factors mentioned earlier.

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