[SN1P3R]

Considering the fact that any R (methyl, ethyl, etc.) group apart from Benzene induces (increases) electrons density in the adjacent molecule I have a question:

In Trimethylamine the lower value of Pka (-log of Ka) (when compared with other Methylamine's and ammonia) is suggested to be a consequence of the fact that it is difficult for the hydrogen (proton) to get to the nitrogen's lone pair, due to stereo-aspects of the methyl groups. However is it not possibly also due to the fact that the electron density at the nitrogen in this molecule would be extremely high (each methyl group increasing it) and so would repel the other electrons that would be coming from the methyl groups, thus causing it not to be as electron rich and not as good of a base as expected?

Please give any speculation even if it is obvious.

P.s. this is not an assignment I'm just curious, also sorry I'm not an undergraduate, I'm a sixth-form student. lol.

Thnx

[nj_bartel]

However is it not possibly also due to the fact that the electron density at the nitrogen in this molecule would be extremely high (each methyl group increasing it) and so would repel the other electrons that would be coming from the methyl groups, thus causing it not to be as electron rich and not as good of a base as expected?

It seems like you're essentially saying, "Because the nitrogen is such an incredibly basic point, it is preventing additional electrons from gathering at the nitrogen that would make the nitrogen more basic.  Therefore, the nitrogen is not that basic."

[azmanam]

any R (methyl, ethyl, etc.) group apart from Benzene

Not exactly true.  Vinyl (CH=CH₂), cinnamyl (CH=CH-Ph), and other such conjugated groups will also pull electron density away from nitrogen.

However is it not possibly also due to the fact that the electron density at the nitrogen in this molecule would be extremely high

It's high, but the electron density on the nitrogen of trimethylamine is not all that much greater than dimethylamine.

and so would repel the other electrons that would be coming from the methyl groups

No.  The only effect that might have on an intramolecular front would be if there was some other incredibly electronegative group attached to one of the alkyl chains.  The two electronegative groups would probably not associate with each other.  To wit, alpha dicarbonyl compounds orient themselves such that the two oxygen atoms of the carbonyl groups point away from each other. 

The pka trends among alkylated acids isn't that large of a gap.  Alkyl groups just don't perturb the electron density map as much as, say, halogens or aryl groups:

compound                                                              pka
protonated ethylamine                                             10
protonated phenylamine (or protonated aniline)            4.6
protonated dimethylphenylamine (dimethylaniline)         5.2
protonated diphenylamine                                         0.78

Adding one aryl group drops the pka almost 5 units.  Adding another aryl group drops it almost another 5. Adding 2 methyl groups only raises is 0.6 pka units.

[SN1P3R]

Kk, thats great, thank you alot to both of you, especially Azmanam, really helped.

[macman104]

I think what was being asked was, when you compare a trend like:  methylamine to dimethylamine to trimethylamine, you see the pka of the protonated species drop from:

10.73, 10.64 to 9.79.  This indicates that the conjugate acid of trimethylamine is the strongest, and the weakest base, no?  Based purely on inductive effects of the methyl groups on the amine, you would expect trimethylamine to be the most basic, as the electron push into the nitrogen lone pair is the greatest.

A similar thread was posted about the same topic, where rico gives a very thorough answer:

http://www.chemicalforums.com/index.php?topic=23571.0

[SN1P3R]

Just to let you know, i've decided to replace the nitrate with flour, this, i have decided will most likely lead to a better cake!

Thnx for all the, help.

[macman104]

Just to let you know, i've decided to replace the nitrate with flour, this, i have decided will most likely lead to a better cake!

Thnx for all the, help.