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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: sun725 on May 13, 2017, 12:56:13 PM

Title: Electrophilic and Nucleophilic site(s)
Post by: sun725 on May 13, 2017, 12:56:13 PM
I have to indicate the electrophilic and nucleophilic site(s) on this molecule:

http://imgur.com/a/72qfm

The only nucleophilic site that I can see is the hydroxy group on the Phenol. The carbonyl oxygen is more of a Lewis base than a nucleophile. Anyone who can confirm this or help me with this?
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: Dan on May 14, 2017, 12:36:46 AM
Yes, the phenol is nuclophilic, and the ketone is not.

What about electrophilic centres, what do you think?

What other functional groups do you have there? Have you tried looking up the reactivity of those functional groups (textbook or online) and seeing whether they tend to behave as nucleophiles or electrophiles (or neither)?

Title: Re: Electrophilic and Nucleophilic site(s)
Post by: rolnor on May 14, 2017, 01:08:06 AM
Also the very large iodines make the phenol a very stericaly hindered nucleophile, I think it would be difficult to for example esterify it.
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: sun725 on May 14, 2017, 05:12:39 AM
Well, we do have 3 functional groups present here. The ketone, the benzofuran and the phenol. The phenol is nucleophilic, but the ketone is electrophilic or the carbon attached to the carbonyl group is. I didn't find anything regarding the benzofuran but I guess it's the lone pairs on the oxygen that makes it nucleophilic? I feel a bit lost here ...
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: sun725 on May 15, 2017, 02:22:06 AM
Yes, the phenol is nuclophilic, and the ketone is not.

What about electrophilic centres, what do you think?

What other functional groups do you have there? Have you tried looking up the reactivity of those functional groups (textbook or online) and seeing whether they tend to behave as nucleophiles or electrophiles (or neither)?

As mentioned the hydroxy group (oxygen) is nucleophilic, however the oxygen on the ketone can be protonated and acts as a nucleophile as well. Then we have the two aromatic rings. They can both act as nucleophiles and electrophiles. I asked my professor. Now I'm really not sure about anything. Whats's right and what's wrong here. Really hoping you can help and clarify this.

Title: Re: Electrophilic and Nucleophilic site(s)
Post by: Dan on May 15, 2017, 08:08:00 PM
I didn't find anything regarding the benzofuran but I guess it's the lone pairs on the oxygen that makes it nucleophilic? I feel a bit lost here ...

There should be reactions with benzofurans shown in your organic chemistry textbook
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: sun725 on May 16, 2017, 01:11:15 AM
Well, I've looked through my textbook many times without finding anything unfortuneatly.
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: wildfyr on May 16, 2017, 03:30:11 AM

...however the oxygen on the ketone can be protonated and acts as a nucleophile as well.
[/quote]

No. Protonating the ketone in fact makes it more electrophilic.
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: sun725 on May 16, 2017, 07:59:26 AM

...however the oxygen on the ketone can be protonated and acts as a nucleophile as well.

No. Protonating the ketone in fact makes it more electrophilic.
[/quote]

I believe you. What can I say. My professor said that and I don't know what to write anymore.
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: wildfyr on May 16, 2017, 08:03:47 AM
They must have misspoken. I'm sure they know this. Think of it this way: in acid catalyzed transesterification, what is the first step? Protonation of the oxygen of the carbonyl, because an alcohol can't just attack the carbon center of an unprotonated carbonyl.
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: Dan on May 16, 2017, 08:00:30 PM
Well, I've looked through my textbook many times without finding anything unfortuneatly.

It should be in the aromatic heterocycle chapter, but if there is nothing specifically about benzofurans you can look at relatives like furan and indole to get an idea. What books do you have?
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: lb2 on May 16, 2017, 08:43:32 PM
@sun725

Quote
the oxygen on the ketone can be protonated and acts as a nucleophile as well

I think you are just tripping up on what your instructor said. He didn't mean that the oxygen can be protonated, and once protonated it can act as a nucleophile. He meant that the oxygen can be protonated or, alternatively, it can also act as a nucleophile.
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: sun725 on May 17, 2017, 05:21:39 AM
Well, I've looked through my textbook many times without finding anything unfortuneatly.

It should be in the aromatic heterocycle chapter, but if there is nothing specifically about benzofurans you can look at relatives like furan and indole to get an idea. What books do you have?

Just to be 100 % sure. I've marked the two aromatic rings, as well as the hydroxy group and the oxygen attached to the ketone and the one attached to the benzofuran as nucleophilic. I don't know any relevant reaction to use here when looking at the ketone (all the reactions I've found regarding this are addition of a nucleophile to a ketone)?. I found a single reaction in my book regarding the furan, where a pyrrole is obtained.
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: rolnor on May 17, 2017, 07:29:01 AM
Is not a benzofurane to resonancestabilized to give the reaction to obtaine a benzopyrolle?
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: sun725 on May 17, 2017, 08:37:52 AM
Is not a benzofurane to resonancestabilized to give the reaction to obtaine a benzopyrolle?

Didn't quite get that?
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: rolnor on May 18, 2017, 12:32:53 AM
To convert a furan to pyroll you need to open the ring and disrupt the aromatic system, this is possible in a furan because the aromaticity is weak, in a benzofuran the aromaticity is muck stronger.
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: sun725 on May 19, 2017, 08:28:16 AM
This is the molecule I'm working with
http://imgur.com/a/dIDs4

I have to make a reaction with EVERY nucleophilic site on the molecule, and I want to know if this reaction is correct?
http://imgur.com/a/zESNg

My instructor is very sure about the ketone being nucleophilic, therefore I've to find a reaction here as well. Can the ketone here be acid catalyzed? Or is there steric hindrance?

I hope someone can help me with this. This assignment has to be handed in no time. I appreciate the *delete me* Thanks a lot.
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: rolnor on May 19, 2017, 08:40:46 AM
Its impossible to substitute the oxygen in benzofurane this way, its phenolic?
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: sun725 on May 21, 2017, 06:12:37 AM
Well, I've looked through my textbook many times without finding anything unfortuneatly.

It should be in the aromatic heterocycle chapter, but if there is nothing specifically about benzofurans you can look at relatives like furan and indole to get an idea. What books do you have?


I have McMurry Organic Chemistry.
Can you please give me a convincing argument claiming the the ketone, or the carbonyl oxygen in the ketone is not nucleophilic. I really don't know what to write anymore. Everyone says something different. My instructor literally said that the Ketone oxygen can also be protonated, thus reacting it as nucleophile. My assignment is due and I want to write the right thing. So please, if you could clarify this. Thanks   
Title: Re: Electrophilic and Nucleophilic site(s)
Post by: Dan on May 21, 2017, 08:05:39 PM
I really don't know what to write anymore. Everyone says something different. My instructor literally said that the Ketone oxygen can also be protonated, thus reacting it as nucleophile.

OK, I suppose you could make that argument. The issue here is that nucleophilicity is a scale, so when a question asks to identify the nucleophiles, I guess most people (including me) would point at the decent nucleophiles, not just every lone pair of electrons. Your instructor appears to want you to identify every site that could theoretically act as a Lewis base. It's an odd phrasing for that exercise, which is why you are getting conflicting answers.