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Can someone me

  1. Apr 9, 2007 #1
    Can someone plz help me...

    I have a few questions to ask.. if someone can help I will very thankfull..
    1st: Can someone explain to me the para, ortho, and meta effects of subsituents on the acidity of benzoic acid..
    2nd: Can HNMR be used to distinguish ortho-ethyl benzaldehyde, meta-ethyl benzaldehyde, and para-ethyl benzaldehde..
  2. jcsd
  3. Apr 10, 2007 #2
    If the group is an electron donating group (+R/+I), then the acidity of benzoic acid decreases. Opposite when an ewg is present (-R/-I).

    In the ortho and para position, the groups can partake in resonance, and the resonance effect is greater than the inductive effect. Hence, the +R/-R groups effect the acidity more than the +I/-I groups. If a group is present on the ortho position, and it can form H-bonds, it will do so with th -COOH group present.

    In the meta position, the groups do not undergo resonance with the benzene ring and can only show their +I/-I effect.
  4. Apr 10, 2007 #3


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    Yes, NMR can be used to determine the differences between ortho, meta and para substitution. You can see that there will be one ortho proton remaining for ortho-ethylbenzaldehyde. This proton will be split by the others in the benzene ring but should be far enough from the others to be completely resolved. Integtration will give a 1:4 ratio with the other aromatic protons. Para-substitution will yield only two unique aromatic protons by introducing a C2 symmetry element. Both ortho protons will be identical (no ortho-ortho coupling) and both meta protons will be identical (no meta-meta coupling). The result is a pair of resolved doublets that integrate 1:1. You can see the spectra for yourself at the following site:

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