Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Big-Daddy on February 03, 2014, 05:17:52 PM
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Is it a decent generalization for simple cases to suggest that (when solvated) a primary amine is likelier to be deprotonated than a secondary amine, which is likelier than a tertiary amine (i.e. pKa is lowest for primary amines and highest for tertiary amines in general)? Conversely it would be the case that a tertiary amine is likeliest to be protonated (i.e. lowest pKb), followed by a secondary amine, followed by a primary amine. Of course, if there is any positive N, it will accept no more protons and will instead be likeliest of all to unload the proton it has.
I want to know about how imine acidity/basicity would work. Does the C=N make the nitrogen more basic (if it is tertiary), or more acidic (if it is secondary)? Compared to the amine?
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I would say its similar like amines, but additionally the double bond can have some influence, that an addition could take place. The +I-effect of alkyl-substiutes stabilize the system.
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This trend is not valid if the N is part of a heterocyclic ring or conjugated. For example, nitrotetrazole has a pka of -0.8. Or if your secondary nitrogen is part of a nitraminine, it is again acidic.
really hard to generalize here.
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I would say its similar like amines, but additionally the double bond can have some influence, that an addition could take place. The +I-effect of alkyl-substiutes stabilize the system.
So the increased stability will usually lead to the =N-H being more favoured for deprotonation than primary, secondary or tertiary amine and =N-C being more favoured for protonation than the primary, secondary or tertiary amine? I suppose if =N-H is more favoured for deprotonation than the amines, typically, =N-H will be less favoured than the amines usually for protonation (i.e. to make =NH2+)?