March 29, 2024, 05:53:24 AM
Forum Rules: Read This Before Posting


Topic: Acidity of N  (Read 2037 times)

0 Members and 1 Guest are viewing this topic.

Offline Big-Daddy

  • Sr. Member
  • *****
  • Posts: 1177
  • Mole Snacks: +28/-94
Acidity of N
« on: February 03, 2014, 05:17:52 PM »
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?

Offline Hunter2

  • Sr. Member
  • *****
  • Posts: 2155
  • Mole Snacks: +162/-47
  • Gender: Male
  • Vena Lausa moris pax drux bis totis
Re: Acidity of N
« Reply #1 on: February 04, 2014, 03:10:30 AM »
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.

Offline 408

  • Chemist
  • Full Member
  • *
  • Posts: 796
  • Mole Snacks: +103/-30
Re: Acidity of N
« Reply #2 on: February 04, 2014, 10:52:27 AM »
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.

Offline Big-Daddy

  • Sr. Member
  • *****
  • Posts: 1177
  • Mole Snacks: +28/-94
Re: Acidity of N
« Reply #3 on: February 04, 2014, 12:27:05 PM »
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+)?

Sponsored Links