Question

Need some quick help with finding the weakest base.

Answer 1

https://gyazo.com/edaab3b0f8290f61f869852ee6252cf4

HEres a screenshot of the problem i am working on. I need to find which base is likely the weakest. I want to say its going to be Norepinephrine, but I dont know how to explain why...

Answer 2

Well what's different about it that's giving you that hunch? What kinda stuff do you know about base strength in general? I'll help you figure out how to put your ideas into more concrete language.

Answer 3

Now that I think about it, I'm thinking Methyltramine. The nitrogen would be pulling the electrons towards it, making the electron cloud more dense in that area. Epinephrine has this same effect, but it also has the oxygen in the middle pulling some as well.

Answer 4

@Kainui

Answer 5

Ahh ok OS just crashed on me and I lost all my message, so I'll try to say it quick and short.

The atom on each of these molecules which is the most basic is going to be the nitrogen with it's lone pair of electrons. Being a good base means having the ability to donate electrons, so having a lot of electron density makes something a good base.

Your reasoning is right about Epinephrine, oxygen is an electron withdrawing group and it's near enough to make Epinephrine and Norepinephrine weaker bases than Methyltyramine, since Methyltyramine has no electron withdrawing group. SO Methyltyramine ends up being the best base partially because of this.

The other main factor to consider is this methyl group. Carbon is electron donating, so it will make Methyltyramine an even better base, and also make Epinephrine a better base than Norepinephrine.

So to be clear as possible since I get kind of wordy, Norepinephrine has no extra methyl group to give it electron density AND it has an oxygen withdrawing electron density, so it has very little electron density to give, making it a poor base.

Just as a fun remark, the aromatic OH group is really too far off to matter much, it might if we're considering intramolecular effects or if there was a longer "leash" on the nitrogen it could interact with itself intermolecularly but these are just some random thoughts for fun don't worry about this too much.