Acid strenth of aromatic organic molecules

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Discussion Overview

The discussion revolves around determining the acid strength of various aromatic organic molecules, specifically those with hydroxyl (OH) and nitro (NO2) groups attached to a benzene ring. Participants explore the factors influencing acid strength, including the stability of conjugate bases and the polarization of O-H bonds.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that a strong acid is characterized by a stable conjugate base formed after the acid loses a proton.
  • Others propose that the extent of polarization of the O-H bond influences acid strength, with more polarized bonds facilitating the release of H+ ions.
  • It is noted that certain substituents can withdraw electrons from the O-H bond, enhancing ionization ('inductive effects'), while groups like CH3 may push electrons into the bond, making ionization more difficult.
  • A later reply highlights that for compounds like p-nitrophenol, resonance stabilization of the conjugate base also plays a significant role, which is dependent on the position of the -NO2 substituent.

Areas of Agreement / Disagreement

Participants express various viewpoints on the factors affecting acid strength, indicating that multiple competing views remain without a clear consensus on the order of acid strength for the discussed compounds.

Contextual Notes

Participants mention the importance of understanding inductive effects and resonance stabilization, but the discussion does not resolve the specific assumptions or definitions related to these concepts.

Libra_girl
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CH3CH2CH2CH2OH

A benzene ring with an OH group attached on the top and a NO2 group attached at the bottom.


A benzene ring with an OH group attached on the top and a CH3 group attached at the bottom.


A benzene ring with an OH group attached on the top


And my question is, how do you determine the compounds in order of decreasing acid strength?
 
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hint:

a strong acid is one having a stable conjugate base(that is the anion formed after it loses a proton).

or the extent to which the O - H bond is polarised. the more polarised it is, the easier the H+
 
Kushal said:
hint:

a strong acid is one having a stable conjugate base(that is the anion formed after it loses a proton).

or the extent to which the O - H bond is polarised. the more polarised it is, the easier the H+
is released.*edit* a mistake in posting...
 
Kushal said:
hint:

a strong acid is one having a stable conjugate base(that is the anion formed after it loses a proton).

or the extent to which the O - H bond is polarised. the more polarised it is, the easier the H+


IOW some groups are considered to withdraw electrons from that O-H bond making it easier to ionize ('inductive effects') while other groups like CH3- will push electrons more into the bond making it harder and any appropriate chemistry textbook will contain examples and illustrations that the chemistry student is suppose to familiarise self with. Should also study how these effects work out for amines. For p-nitrophenol, your second example there is an additional mechanism of resonance stabilisation of the conjugate base, which depends on the position of the -NO2 substituent that you need to know about (and like the other effects matter for reactivity, not just acid strength).
 

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