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91
Organic Chemistry Forum / Re: Additional Resonance Structure?
« Last post by hollytara on May 27, 2020, 06:23:26 PM »
I think people sometimes leave off the other aromatic resonance structure because "everybody knows" it exists. 

But of course it is equally important to the one shown. 

92
Organic Chemistry Forum / Re: Question about aromaticity of bicycles
« Last post by hollytara on May 27, 2020, 06:00:37 PM »
The transannular pi interactions across the bridge make Huckel not strictly applicable. 

look at Dougherty and Anslyn

or any other Physical organic book.
93
Organic Chemistry Forum / Question about aromaticity of bicycles
« Last post by OrganicH2O on May 27, 2020, 05:13:20 PM »
I have read that Huckel's rule only strictly applies to single ring systems, but I don't completely understand what that means.

I attached a picture of two molecules I have seen described in multiple different ways by different textbook authors, naphthalene and indole. Both could be described as aromatic because they have a large ten electron pi system, or two smaller 6 electron pi systems. Is one of these descriptions substantially more correct than the other, or are both descriptors correct? And what would be the reasoning behind that decision?

Any wise words on this topic, and/or suggestions for textbook passages to read, would be greatly appreciated.
94
I have a question about how the number of alpha hydrogens effects the ease or Robinson Annulation. I attached a picture which illustrates my question.

In reaction 1 in the picture, the 1,3-diketone has two alpha hydrogens. Following Michael addition, the ground state would be the doubly stabilize enolate ion shown. I hypothesize that this stable enolate will slow down subsequent aldol cyclization. This aldol cyclization is possible, but  might require harsher conditions like higher temperature and longer reaction times.

In reaction 2, the 1,3-diketone has only one alpha hydrogen. Therefore, formation fo the an especially stable enolate is not possible. Subsequent aldol cyclization would therefore be much faster. It might even be impossible to stop the aldol cyclization.

Is this speculation logical and correct?
95
Organic Chemistry Forum / Re: Additional Resonance Structure?
« Last post by spirochete on May 27, 2020, 04:27:23 PM »
You are 100% correct. That is an additional resonance structure. It is equivalent to the other "most important" resonance contributor. So there are really two equally important resonance contributors.

I think this other resonance structure is "less interesting" in some ways because it doesn't show a separate atom carrying the negative charge. But that doesn't negate from the fact that it's a resonance contributor. In a  very rough sense, that resonance structure helps show the aromaticity of the benzene ring.
96
Organic Chemistry Forum / Re: question is find the reagents
« Last post by hollytara on May 27, 2020, 01:58:04 PM »
This translation will help you:

PCC is pyridinium chlorochromate
NBS is N-bromosuccinimide

HBr is HBr (hydrobromic acid)
97
Organic Chemistry Forum / Re: Basicity of Substituted Pyridine
« Last post by AlphaScent on May 27, 2020, 12:32:52 PM »
I thought about acid hydrolysis and would just keep it cold as hollytara said.  I have never had too much trouble with secondary acetates hydrolyzing when I keep it cold. 

Thank you for the input.  I am trying to be able to scale up a reaction to 500 g so I am trying to not have to do any rigorous CC.  Hopefully only a plug at most.

I am doing a rxn tomorrow and will get back to you about how it goes.

Cheers!
98
Organic Chemistry Forum / Re: Basicity of Substituted Pyridine
« Last post by hollytara on May 27, 2020, 11:53:32 AM »
pKa of the methyl ester of the 4-carboxylic acid isomer is 3.45.  If it is the same for the 2 isomer and the cyclohexyl , then to protonate you will have to bring pH down to 2 or less. 

That can hydrolyze the ester.  I would test on a small amount to make sure and do the process quickly and at low temperature (maybe keep solutions in ice bath).  This will limit the hydrolysis.
99
Generic Discussion / Re: Introduce Yourself
« Last post by kaanttlc on May 27, 2020, 11:38:27 AM »
Hi everyone :)

My name is Kaan. I am 22 years old. I'm from Turkey and I study at Trakya University, and I am a chemistry student.
Currently living at the Istanbul w/my family because of the coronavirus, I hope everybody is safe. Glad to meet you guys. #stayhome
100
Organic Chemistry Forum / question is find the reagents
« Last post by kaanttlc on May 27, 2020, 11:27:21 AM »
i did the rest of it but didn't these three, if anyone can, can he write it, thanks.. (sorry for my english)
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