First of all let me say that my doubts may sound dumb, but I do not have a background on chemistry. I understand the theory behind protonation and
deprotonation, but I can't get the structure of protonated and deprotonated DMAP (4-dimethylaminopyridine) and methyl p-toluenesulfonate.
Can someone help me, please?
Thank you so much!vmelkon - 25-11-2014 at 12:10
For methyl p-toluenesulfonate, the H+ should stick to one of the oxygens on the sulfur.
In the case of 4-dimethylaminopyridine, the H+ can either stick to the lone pair of the N in the ring or the lone pair of the N in the amino group.aga - 25-11-2014 at 12:39
So ...
Protonation is basically an H+ sticking on somewhere, and
Deprotonation an H+ getting slapped off ?Chemosynthesis - 25-11-2014 at 12:51
^ Yes. Generally these occur on either an electronegative atom (see how often N or O is charged, both of which are on a Zwitterion such as an amino
acid at physiological pH of 7.4 in blood or 7.2 intracellularly), or on an atom that allows resonance stabilization (ex. enolate acidic alpha
hydrogens).aga - 25-11-2014 at 12:59
So ...
In OC some bits of the molecule are more susceptible than others to having an H+ stuck on or one slapped off ?Chemosynthesis - 25-11-2014 at 13:37
OC?
Yes, some regions of molecules are more susceptible to protonation or de-protonation than others. This is part of the utility of pKa tables, as it is
a very useful way to visualize what present functional group is likely to react first/next based on what form (protonated/de-protonated) they are in
(dependent on solvent and pH). It also is useful in determining solubility for an acid/base liquid-liquid solvent extraction, isoelectric point
precipitation or a titration.Darkstar - 25-11-2014 at 14:03
Yes, some regions of molecules are more susceptible to protonation or de-protonation than others.
It might be worth mentioning to the OP that in the case of DMAP, the ring nitrogen is more basic than the amino group nitrogen and more likely to be
protonated first.aga - 25-11-2014 at 15:42
OC as in Organic Chemistry.
Are there pKa tables for Organic compounds with some of their bits in different states ?
Noob question, as i have not done much OC.Chemosynthesis - 25-11-2014 at 16:21
It might be worth mentioning to the OP that in the case of DMAP, the ring nitrogen is more basic than the amino group nitrogen and more likely to be
protonated first.
Good idea. I took Vmelkon's order as implicitly prioritized, but it is probably best to state it definitively.
Are there pKa tables for Organic compounds with some of their bits in different states ?
Noob question, as i have not done much OC.
Ah! Yes. There are tables for various pKa values of compounds in different solvents.
I would highly recommend a copy of Lange's or the CRC Handbooks. The Merck Index is also good. I have digital copies of all three, and a hardcopy of a
CRC on my desk right here. To be honest, I usually use software for all that kind of thing now, though.
