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WTF is more basic:

Discussion in 'MCAT Discussions' started by farleyisgod, Apr 13, 2004.

  1. farleyisgod

    farleyisgod you big dummy
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    trimethyl amine
    or dimethyl amine

    I always thought diethyl because of steric issues.
    This solution I'm staring at says otherwise.

    Thanks.
     
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  3. Cerberus

    Cerberus Heroic Necromancer
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    methyl or ethyl?
     
  4. akalin24

    akalin24 Member
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    Trimethylamine is more basic. Alkyl groups are electron donating!
     
  5. UCLAstudent

    UCLAstudent I'm a luck dragon!
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    The OP is correct. Amine basicity goes in this order: secondary>tertiary=primary>ammonia
     
  6. farleyisgod

    farleyisgod you big dummy
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    revenge must be sweet.
     
  7. farleyisgod

    farleyisgod you big dummy
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    thanks! :thumbup:
    another reason to flush my Kaplan materials down the toilet :/
     
  8. akalin24

    akalin24 Member
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    The more highly substituted the amine with electron releasing alkyl groups, the more basic the amine!!

    (CH3)3N > (CH3)2NH > CH3NH2 > NH3

    Decreasing order of base strength based on electron releasing groups.

    I took this directly out of my undergrad Orgo text. I believe it's accurate.
     
  9. UCLAstudent

    UCLAstudent I'm a luck dragon!
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    And I took what I said out of my chem. textbook, as well.

    Since we seem to have conflicting sources, I am going to guess that it depends on what exactly the substituents are. If the electron-donating groups are all methyls, then it's likely that tertiary will be most basic because methyl groups aren't so big. If the groups are phenyls, that may be enough steric hindrance to cause secondary to be more basic.

    Just a thought. :)
     
  10. babinski bob

    babinski bob Senior Member
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    Remember the MCAT is a thinking test. The idea is that alkyl groups are e- releasing. 3 > 2 > 1 > NH3. Don't confuse steric hindrance w/ basicity. Steric hindrance will certainly decrease nucleophilicity but NOT basicity. I can positively 100% confirm this statement.
     
  11. farleyisgod

    farleyisgod you big dummy
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    Let's hope the question doesn't come up on the MCAT... or if it does, the substituents are at least the size of an ethyl group.

    !!

    good luck, everyone. I'm off to eat dinner and watch 24.
     
  12. UCLAstudent

    UCLAstudent I'm a luck dragon!
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    I will have to think this over and figure out what my textbook is saying. :rolleyes:
     
  13. blz

    blz Senior Member
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    It's trimethyl amine.
     
  14. babinski bob

    babinski bob Senior Member
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    The reason why there's different answers and opinions regarding this question is that when looking at basicity, you have to consider solvent effects. Therefore, you'll find different answers depending on the solvent used. In the gaseous phase (where there is no solvent) which is the truest measurement of inherent acidity/basicity, basicities follow 3>2>1>NH3. In some solvents the trend might be 2>3>1>NH3. The MCAT is not interested in testing you on PhD level theory. In all liklihood, you wouldnt get a question asking you to rank trimethyl, dimethyl, methylamine, ammonia. You should however, understand that alkyl groups are e- donating andwill therefore increase the basicity. Therefore, dimethylamine is always more basic than ammonia. And both of these guys are more basic than aniline. These are the types of important concepts to know. You guys seem like you already understand this quite well. Good luck with the mcat. Keep it simple and you'll rock the ochem questions.
     
  15. blz

    blz Senior Member
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    I couldn't agree anymore. KEEP IT SIMPLE! from what I've seen in the MCAT quiz thread, you guys are losing sight of this concept.
     
  16. farleyisgod

    farleyisgod you big dummy
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    I'm all for keeping it simple, but I'm more for knowing the right answer. I'm not just pulling theories out of my ass... one book says it one way, the other book says it the other.

    :(
     
  17. indo

    indo Feed me a stray cat
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    Think about + charge stabilization in those types of base questions. Same thing for acids but with - charge stabilization.
     

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