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Thread: Order of basic strength

  1. #1 Order of basic strength 
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    RNH-> RO-> OH-> CH3COO-

    I know this is the order of decreasing basic strength. Please explain using inductive effect and/or polarity.


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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
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    This looks like homework. Tell us your thoughts and we'll help and point you in the right direction. No one here will do it for you.


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  4. #3  
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    Well I know that basic strength is how well you lose electrons. I know the structures of RNH- and RO- but I can't figure out how one is better at releasing electrons.
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  5. #4  
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    Electrons donation comes into it if you are considering these as Lewis bases, it might be easier to figure it out if you think of them as Bronsted bases. In this case the basicity is how well it will accept a proton. Here are some hints: Think about the electron density around the N or O atoms. How do the substituents affect this via the inductive effect? Is there any reason that the base (or it's conjugate acid) are particularly stable? Answering these questions will tell you why the base strength decreases along this series.
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  6. #5  
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    I have not yet thought it in depth but can I think it this way that N is more electropositive so it will more willingly share with a proton?
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  7. #6  
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    I can't really give you any more hints without doing it for you which isn't going to happen. Post your full answer and I'll see where you need help (if it is not correct).
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  8. #7  
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    I tried to figure out a reason that RNH- is better proton accepter than RO-

    Is it that N has two bonds from where it can hog electrons while O has only one?
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  9. #8  
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    Re-read post #4 and see post #6, I am not going to do it for you, I have given you all the hints I can short of this. Present your full answer and I will help you out where needed.
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  10. #9  
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    In RNH- ,N is getting electrons from R group as well as the hydrogen while in RO- ,oxygen is only getting electrons from the R group.
    So N in RNH- will have more delta negative and will attract more proton than O in RO- (but I am confused that as O is way more electronegative than N so I am missing something)

    Among RO- and OH- , RO- will attract more proton because CH3 groups give electron easily as compared to H (not sure about this).

    Among OH- and CH3COO- , OH will attract more proton because there are two oxygens in acetate which reduces the delta negative on it.(I wasn't able to come up with anything better for this).

    Thanks.
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  11. #10  
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    Your statements about the inductive effect are correct, but remember when I said to think about the stability of the base (or it's conjugate acid)? For the first part as you rightly say oxygen is way more electronegative than nitrogen. This means it is "happier" being negatively charged. RNH- is a stronger base than RO- as that nitrogen really wants a proton to neutralise that negative charge whereas the oxygen is happier to stay charged. You are correct as to why OH- is weaker than RO-, it is just the differing inductive effects of R and H, as for the carboxylate ion at the end, this is a weak base as the ion is stabilised by resonance whereas the conjugate acid is not.
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  12. #11  
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    thanks a lot!
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