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Acid strenth of aromatic organic molecules

  • Chemistry
  • Thread starter Libra_girl
  • Start date
  • #1
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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?
 

Answers and Replies

  • #2
437
1
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+
 
  • #3
437
1
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...
 
  • #4
epenguin
Homework Helper
Gold Member
3,629
701
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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