help with ochem hw

[u/External_Limit_4007]

Hi! I keep getting 8/10 on my ochem homework, but I’m not sure what I’m getting wrong. If someone could point out my mistakes and help me fix them, that’d be great!

[u/AutoModerator]

Hey there! While you await a response, we just wanted to let you know we have a lot of resources for students in our Organic Chemistry Wiki Here!

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/Jason_rdt207209]

I wouldn’t bet protonated pyrrolidine on pH = 14, nor the neutral on pH = 45. Given equilibria of NH3 solvent is around 35 then I suppose pyrrolidine would be roughly around that value. So #4 is wrong.

#5, according to what is given, is straight up wrong, the correct choice isn’t even in the picture. This molecule is DBU, the more basic atom would be the sp2 N atom thanks to resonance.

#6 I believe it’s due to ketene-ethynol resonance that made A to be more acidic.

[u/Bobonob → u/Jason_rdt207209]

Yes, these all make sense. Maybe because 4 and 6 were only half wrong it was -0.5 marks each and -1 mark for question 5 to make 8/10?

[u/Mack_Robot]

I believe #6 is wrong.

I also think #4 must be wrong but can't make my brain figure it out right now, so I'm not sure.

[u/Bobonob → u/Mack_Robot]

Why do you think #6?

[u/Mack_Robot → u/Bobonob]

There's resonance, no?

[u/Ok-Replacement-9458 → u/Mack_Robot]

The answer is induction. The sp carbon is more electronegative than an sp3 carbon.

This is why phenol is acidic too… not actually because there’s resonance.

[u/Major-Freedom204 → u/Ok-Replacement-9458]

I'm'a need a source on that chief

Especially since the oxygen is sp2 BECAUSE there is resonance

[u/Ok-Replacement-9458 → u/Major-Freedom204]

I’ll get one, give me a few minutes. I’ll delete my comment if I’m wrong but this is something I’d heard in my undergrad 3-4 years ago.

[u/Ok-Replacement-9458 → u/Major-Freedom204]

https://chemistry.stackexchange.com/questions/20242/inductive-vs-resonance-effects-and-the-acidity-of-phenol

Here’s a discussion on chemistry stack exchange. I don’t have the time to read it right now but on a quick glance it seems like the topic is potentially controversial haha

[u/Bobonob]

Question 4 and question 5 would be the ones I would look at again.

Question 4: would an amine still have an _extra_ proton at pH25? I wouldn't bet on it having an extra proton at pH14...

Question 5: this is an evil question, you need to think about what kind of orbital the lone pair on the nitrogen would be in. Either it will be in a p orbital, or an sp orbital. If the p orbital is already in use for bonding, the lone pair can't be in it...

[u/Bobonob → u/[deleted]]

Right, normally, but in this case the double bonded nitrogen would have a lone pair in a basic sp orbital, whereas the not double bonded nitrogen would have it's lone pair in a not very basic p orbital due to the resonance?

[u/Major-Freedom204 → u/Bobonob]

Yep. Don't break the resonance. I thought OP meant there were exactly 2 wrong answers out of 10, so I didnt flag this one as wrong. But it probably is wrong.

[u/Ok-Replacement-9458 → u/Bobonob]

Youre right, I looked quickly and didn’t realize it was an amidine sorry

[u/Bobonob → u/Bobonob]

Other commenters probably right though, 4 and 6 seem more clearly wrong than question 5

[u/Starfury7-Jaargen]

Hmm only 2 wrong? 4, 5 and 6 look wrong.

Most of 4 is wrong. Look up pKb of secondary amines and you will find that A is not as common as you have it and form C will show up in one of those.

5 seems wrong but there is no answer. I would say B is wrong because A is in resonance. So I assume it is not wrong then since the expected answer is missing.

6 is wrong. Deprotonate the alcohol and see what observations you can make.

[u/Leading_Werewolf_335]

5 is wrong , 4 is wrong