O chem masters, help!

[sfoksn]

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Hello, I am having a lot of trouble with Ochem..

First of all, K2Cr2O7/H+ is a VERY strong oxidant, right?

How strong is it?

I just don't understand how it works...

For example, on cyclohexanol (cyclic alcohol), it only oxidizes it to cycloketone...

On another example, on a ethyl benzene, it oxidizes it to benzoic acid.

Another time, it oxidizes 2-butanol into just 2-butanone..

Until then, i thought it was able to oxidize straight carbon chains into ketone and could not kick off methyl group and it was able to oxidize alcohols into carboxylic acid no problem.

but the next example threw me off: butyl benzene became just benzoic acid after being oxidized. Which means the carbon group was kicked off..


Now the last example really confuses me.

When does it reduce completely to carboxylic acid, and when is not allowed to kick off carbon groups like methyl?


Also, KMnO4 is allowed to kick off methyl groups to make aldehyde/ketone right?
It maximally oxidizes everything, right?


Thanks for reading and i hope i get some responses...


P.S. ANOTHER QUICK QUESTION, I DO NOT UNDERSTAND THESE TREE REACTIONS:

Benzene-MgCl molecule reacting with 1. 3 membered epoxide ring (2 carbons and 1 oxygen), then treated with H3O...
I thought that MgCl could would leave and epoxide ring would attach to the benzene, and there should be 2 OH's added in anti-fashion.. right?
It turns out that only 1 OH is added to the less substituted carbon.. Why?

m-chloro-nitrobenzene reacting with (CH3)2CuLi in ether -> Why does CH3 replace the chlorine atom? What are the circumstances for this? I thought they would just add to the other meta position because NO2 is such a strong withdrawing group compared to Cl...

Ethyl benzene reacting with NBS, ROOR, and heat -> I thought NBS and ROOR are just like adding HBr with Peroxide, so it should be anti-markovenikov and Br should go on the less subbed carbon... correct? The answer shows that Br is actually added to the carbon right next to the benzene, which is more substituted than the end methyl group....

Sorry for so many questions...

 

[YoYoMa21]

Hey, yeah K2Cr2O7 is a very strong oxidizing agent.

This is how i remember it.... whenever you see a lot of O, think of OXIDATION.

it oxidizes secondary alcohols to ketone (since you can see that secondary alcohol only has 1 H, so that's why it only oxidizes it to ketone), primary alcohol to carboxylic acids, and groups such as methyl, ethyl, butyl, to carboxylic acid.

This is how i remember things... I'm sure others smart pre-dents in here will be able to help you out further....

Hello, I am having a lot of trouble with Ochem..

First of all, K2Cr2O7/H+ is a VERY strong oxidant, right?

How strong is it?

I just don't understand how it works...

For example, on cyclohexanol (cyclic alcohol), it only oxidizes it to cycloketone...

On another example, on a ethyl benzene, it oxidizes it to benzoic acid.

Another time, it oxidizes 2-butanol into just 2-butanone..

Until then, i thought it was able to oxidize straight carbon chains into ketone and could not kick off methyl group and it was able to oxidize alcohols into carboxylic acid no problem.

but the next example threw me off: butyl benzene became just benzoic acid after being oxidized. Which means the carbon group was kicked off..


Now the last example really confuses me.

When does it reduce completely to carboxylic acid, and when is not allowed to kick off carbon groups like methyl?


Also, KMnO4 is allowed to kick off methyl groups to make aldehyde/ketone right?
It maximally oxidizes everything, right?


Thanks for reading and i hope i get some responses...

 

[sfoksn]

bump

can anyone please shed light on this question?

thank you...

 

[hausee]

Benzene-MgCl molecule reacting with 1. 3 membered epoxide ring (2 carbons and 1 oxygen), then treated with H3O...
I thought that MgCl could would leave and epoxide ring would attach to the benzene, and there should be 2 OH's added in anti-fashion.. right?
It turns out that only 1 OH is added to the less substituted carbon.. Why?

Sorry for so many questions...

Benzene-MgCl is like R-MgCl and equivalent to R:- . When react with epoxide, it act as strong nucleophile and attack partically positive carbon. Since it is a pretty big nucleophile, it only attack less substituted carbon. After attached to carbon, C-O break and leave another carbon aquire O and protonated to become -OH.


second Q is similar. (CH3)2CuLi is like CH3:- and attack particially positive carbon attached with Cl. NO2 and Cl are deactivate group and probably will not induce more substitute to benzen ring.

 

[hausee]

Ethyl benzene reacting with NBS, ROOR, and heat -> I thought NBS and ROOR are just like adding HBr with Peroxide, so it should be anti-markovenikov and Br should go on the less subbed carbon... correct? The answer shows that Br is actually added to the carbon right next to the benzene, which is more substituted than the end methyl group....

Sorry for so many questions...

benzyl radical has many resonance structrues (draw them). so Br will add right next to benzyl. another important structure may involve resonance is vinyl.

 

[sfoksn]

AHH

Now i understand the epoxide one. THank you.

I seem to understand the NBS as well....

But hm... radicals gain stability from more substitution, doesn't that mean it wants more electrons?

more donation of electrons to the radical increases its stability, correct?

Then wouldn't being next to strongly EN benzene be worse for it?


Also... I always thought that benzene ring itself cannot be attacked by any bases....

I do not understand how (CH3)2 CuLi can attack the benzene carbon to kick off Cl...

Please enlighten me. I'm horrible at chemistry.🙁🙁🙁🙁

 

[hausee]

AHH

Now i understand the epoxide one. THank you.

I seem to understand the NBS as well....

But hm... radicals gain stability from more substitution, doesn't that mean it wants more electrons?

more donation of electrons to the radical increases its stability, correct?

Then wouldn't being next to strongly EN benzene be worse for it?

Look at benzyl radical resonance structures. its like whole bunch of electrons can move around freely. benzne here is actually share electrons with radical to form conjugated structure.

 

[hausee]

AHH

Also... I always thought that benzene ring itself cannot be attacked by any bases....

I do not understand how (CH3)2 CuLi can attack the benzene carbon to kick off Cl...

Please enlighten me. I'm horrible at chemistry.🙁🙁🙁🙁

Yes benzene it self(without substitute) is pretty stable. But if connected with electronegative substitute like Cl (OK leaving group), it can be attacked with strong nucleotide.

CH3:- is so negative and want to grab anything that positive. Cl make carbon partially positive. once CH3:- is attached to Cl-carbon, which one do you think will mostly like to move out? Which one is stronger acid, HCl or CH4? HCl is stronger acid so its weak conjugated base Cl- will be a good leaving group, thus Cl been kicked off.

cheers.

 

[sfoksn]

Thank you Hausee.

Could you also clarify why the carbon chain group is kicked out by the oxidizing agent as well?

Are they allowed to oxidize ketones to carboxylic acid?

 

[prsndwg]

Q:
on roadmap 6 of 2009 destroyer, why does K2Cr2O7, i guess oxidizes the double cyclohexane? I thought that just happens with benzene rings, replacing the R with COOH :-?

 

[prsndwg]

bump