OChem and Bio questions

[sherry225]

Hi all,

I came up with more questions for the forum..........I think I'm getting addicted to this forum Can someone please explain those two concepts for me?

1. If two molecules of 2-butanone react in aldol reaction, which hydrogen will get pulled off by the base first. To put it another way, which H is more acidic? C1 or C3? and why?

2. Do electron donating groups activate the benzene ring? if so, why?

3. Can someone explain agonistic and antagonistic behavior to me? the Kaplan book only give one example and didn't really explain what it is.....



Thanks for the help!

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[drat]

Hi all,

I came up with more questions for the forum..........I think I'm getting addicted to this forum Can someone please explain those two concepts for me?

1. If two molecules of 2-butanone react in aldol reaction, which hydrogen will get pulled off by the base first. To put it another way, which H is more acidic? C1 or C3? and why?

2. Do electron donating groups activate the benzene ring? if so, why?




Thanks for the help!

1. The C3 hydrogen should be pulled off because that resonance form is most stable. (I believe)

2. And yes, electron donating groups activate the benzene ring for the same reason, resonance.

 

[jheidenr]

2. I visualize it this way...A benzene ring is very happy where it is because its sp2 hybridization puts all of the p-bonds in the same plane, and they all share their electrons. They don't want to share elecrons with anthing else, unless there is a substituent that donates more electrons for them to share with something else. Therefore, an electron donating substuent on a benzene ring activates it for electrophilic aromatic substitution.

3. Generally, agonistic behavior tends to be a threat or dominance display
while antagonistic is a behavior to reduce threat or prevent attack by
appearing submissive or juvenile in behavior.

 

[ScottW3]

1. The C3 hydrogen should be pulled off because that resonance form is most stable. (I believe)

I could be wrong here but I believe it is C1 that is the most acidic. The resonance forms from both options in which the negative charge is transfered to the O are both the same. C1 is a methyl group while C2 is part of an ethyl group. The extra CH3 on C2 is electron donating and will decrease acidity. Someone correct me if I'm wrong.

 

[sinned]

Hi all,

I came up with more questions for the forum..........I think I'm getting addicted to this forum Can someone please explain those two concepts for me?

1. If two molecules of 2-butanone react in aldol reaction, which hydrogen will get pulled off by the base first. To put it another way, which H is more acidic? C1 or C3? and why?

2. Do electron donating groups activate the benzene ring? if so, why?

3. Can someone explain agonistic and antagonistic behavior to me? the Kaplan book only give one example and didn't really explain what it is.....



Thanks for the help!

The thing in an aldol reaction is that the donor, the 2-butanone in this case loses a hydrogen on the most substituted alpha carbon, which is Carbon 3 and forms an enolate ion. Only time it would form an enolate on the least substituted carbon is when you use a reagent such as LDA. Then it undergoes a nucleophilic attack with 2-butanone forming the donor enolate and attacking the carbonyl carbon of the second 2-butanone. So to paraphrase, it forms the products to the most substituted alpha carbon unless you use LDA as the reagent.

Don't think of acidity/basicity on aldol rxns, just think of most and least substituted...

 

[drat]

I could be wrong here but I believe it is C1 that is the most acidic. The resonance forms from both options in which the negative charge is transfered to the O are both the same. C1 is a methyl group while C2 is part of an ethyl group. The extra CH3 on C2 is electron donating and will decrease acidity. Someone correct me if I'm wrong.

From a kinetic standpoint, the C1 is the most acidic because it is the least sterically hindered of the two, but from a thermodynamic standpoint, the double bond between the C2 and C3 will be favored. The pKa between the two (C1 vs. C3) is so minor it is negligible. They are both alpha carbons. You can selectively cleave a H from the C1 by using a sterically hindered base such as LDA and LTMP, or if you want to pluck off a H from C3, use something like MDA.

And if you don't understand what I'm talking about, that's good because this is specific stuff that you would only need to know in graduate school! The DAT would not have a question like this. I would think that they would be more inclined to ask if beta carbon hydrogens or alpha carbon hydrogens on a ketone are more acidic.



And Scott, you make a good point that the methyl group on the ethyl group is electron donating so it would be bad to push electrons towards an already negative charge...I agree...but from the thermodynamic standpoint, do you think it makes sense to have a more "substituted" double bond?

Anyway, tough question and perhaps something that can only be determined experimentally.

 

[ScottW3]

Ah, I see. Now I remember why I didn't like orgo. No, I actually did like it. That makes sense. I've been in DAT orgo mode for so long I've forgotten the real specific orgo. Thanks for the correction.

 

[sherry225]

3. Generally, agonistic behavior tends to be a threat or dominance display
while antagonistic is a behavior to reduce threat or prevent attack by
appearing submissive or juvenile in behavior.

um.....but i read in Kaplan book that agonistic display can be a dog's display of 'appeasement' when it wags its tails. And antagonistic behavior is when it directs its face straight and raises its body......this sounds opposite to what you said. Do you know which one is right? or am I just getting confused.......

 

[jheidenr]

No, I'm pretty sure that's right....here's a couple more definitions for agonistic behavior:

Refers to the behavior associated with aggression and escape behavior. (H) A broad class of behavior that includes all attack, threat, appeasement, and flight behavior. (V)

aggressive, negative behaviors, such as fighting, threatening, and fleeing​

So Kaplan is right about saying that an example of agonistic behavior includes appeasment. I know what you mean though, they did not define the terms, just gave vague examples. When they say that a display of antagonistic behavior whould be when the dog directs its face straight and raises its body, this could mean anything.

The two terms can be confusing, especially because "antagonistic" has taken on a different context in our society. For example, in a book or a play you have the protagonist, i.e. the hero, and the antagonist, ie the villain. But the actual definition of an antagonist is something that couteracts the effects or nullifies the actions of another, such as an antagonist drug in the pharmeceutical sense. Antagonistic behavior is not villainous, it is just couteracting the aggressive displays of its opponents.

 

[sherry225]

Thanks,

That was a great explaination and example.