Which do you think would be more basic?

[Neil45]

NH3 or N(CH3)3 (nitrogen bonded to 3 methyl groups)?

I vote for the latter because methyl is electron donating; electron donating groups increase the basicity of the compound. Is this right?

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[Neil45]

.

 

[DAT12]

I believe it's NH3. Because it itself is known as a very good base. Also the methyl makes it buy slowing it down but you are very right that methyl is donating.

 

[facecrime]

I believe this question came in DAT last year

 

[bharat008]

I think NH3 is a better base because bases are always negatively charged so having more R groups would destabilize the base, making it weaker. Therefore, N(CH3)3 is a weaker base compared to NH3.

 

[DAT12]

Face crime what we the answer?
And after posting my answer I seem to think actually n(ch3)2 is stronger bec electron donating groups especially in water due to h bonding.
But if u had n(ch3)3 that would e stronger in non polar(not h2o) but weaker than n(ch3)2 in h2o

 

[Neil45]

I decided to google search the pka's of both ammonia and trimethylamine, and it seems that trimethylamine is more basic since it has a higher pka of 9.7; whereas, the pka of ammonia is 9.25.

 

[Neil45]

I think NH3 is a better base because bases are always negatively charged so having more R groups would destabilize the base, making it weaker. Therefore, N(CH3)3 is a weaker base compared to NH3.

Hmmmm. I thought destabilization increases the bascity? Electron donating alkyl groups destabilize the carbanions by increasing localized negative charge which favours bascity.

Someone correct me on this.

 

[Neil45]

.

 

[jwest88]

Trimethylamine will be more basic because the conjugate acid has a positive charge that is stabilized by the three methyl groups which are electron donating.

 

[Dentalbum]

I looked at this post a couple days ago and I thought the answer would be trimethylamine since the methyls are donating groups but that's not the case in this situation. I am currently taking organic II and just had lecture over amine chemistry. I had just learned why trimethylamine would be more basic and had to come on here to share. If the question was asking to compare ammonia with methylamine, dimethylamine, or any alkyl group around the nitrogen, ammonia would be less basic. When there is a tertiary amine surrounded by three methyls or three alkyl groups it becomes less basic, and ammonia would be the more basic one. This is called steric hindrance to solvation, meaning that since the amine is sterically hindered, by the three methyls or any alkyl group, it is harder for nitrogen's lone pair to be taken, for instance, by water(that's where the solvation comes in). Ammonia only has three hydrogens around it, therefore nitrogen's lone pair in ammonia is readily available and would be more basic. Hope this helped.
Also to confirm which is more basic look at pkb values, not pka

 

[Neil45]

I looked at this post a couple days ago and I thought the answer would be trimethylamine since the methyls are donating groups but that's not the case in this situation. I am currently taking organic II and just had lecture over amine chemistry. I had just learned why trimethylamine would be more basic and had to come on here to share. If the question was asking to compare ammonia with methylamine, dimethylamine, or any alkyl group around the nitrogen, ammonia would be less basic. When there is a tertiary amine surrounded by three methyls or three alkyl groups it becomes less basic, and ammonia would be the more basic one. This is called steric hindrance to solvation, meaning that since the amine is sterically hindered, by the three methyls or any alkyl group, it is harder for nitrogen's lone pair to be taken, for instance, by water(that's where the solvation comes in). Ammonia only has three hydrogens around it, therefore nitrogen's lone pair in ammonia is readily available and would be more basic. Hope this helped.
Also to confirm which is more basic look at pkb values, not pka

Excellent, thanks. I just looked up the pKb values (http://www.sanderkok.com/techniques/laboratory/pka_pkb.html) and ammonia (pkb 9.25) has a lower pkb than trimethylamine (pkb of 9.81), so ammonia is definitely more basic.

 

[DAT12]

Dentalbum:
Depends on solvent no?

 

[ttpharm]

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