Organic Chemistry

Started by Gholam2020
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Gholam2020

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Hello Everyone,
Could you please explain on why 3 amines are more acidic than primary amine. Base on my understanding the donating group would decrease the acidity but in case of amine it seem to not matter. Please clear that up for me. thanks
 
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Gholam2020 said:
Hello Everyone,
Could you please explain on why 3 amines are more acidic than primary amine. Base on my understanding the donating group would decrease the acidity but in case of amine it seem to not matter. Please clear that up for me. thanks
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You seem very confused. The tertiary amine is generally more basic than secondary or primary especially in the gas phase. Why ? Let us examine the ammonium salt from each. The protonated ammonium salt from a tertiary amine has 3 R groups donating electrons to help stabilize the ion......while the secondary ammonium ion has only 2.....and the primary only 1. The tertiary is the most stable since more stability results in the protonated ion. Thus.....having 3 alkyl groups will generally make the amine MORE BASIC. For an exam like the DAT .....use this as a rule..... The tertiary amine will beat out secondary and primary amines in BASICITY. Now,,,,,in Advanced Organic Chemistry, things get a bit more complicated.......a secondary amine is generally more basic than a tertiary amine in an aqueous solution !!!! Why ? There is a now a new factor involved in stabilizing the ammonium ion, and that is hydrogen bonding !!!! It turns out that a secondary amine has 2 alkyl groups, and can participate in hydrogen bonding........this evidently trumps having 3 alkyl groups only !!!!! However, for the DAT exam......assume that they are discussing the gas phase.....and remember.....tertiary amines are usually more basic than primary and secondary.

Hope this helps.

Dr. Jim Romano
 
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