About oxidation and reduction in organic Chemistry

[samy4408]

TL;DR

A problem with the concept of oxidation and reduction in organic chemistry .

We studied in chemistry that the concept of oxidation and reduction is the exchange of electrons between two chemical substance ,but when i started to study organic chemistry i saw that when we talk about for example the oxidation of a compound it can loss atoms and change his constitution .That seems not compatible with the first definition

 

[jim mcnamara]

Have you learned about redox potential? Redox (reduction/oxidation) is "all about electrons", which is a way to understand what you are asking.

Maybe this will help, if it is too advanced we can help you find something better.
https://www.sciencedirect.com/topics/earth-and-planetary-sciences/redox-potential

 

[Borek]

You do know that converting SO₂ to SO₃ is an oxidation? Same about MnO₂ to MnO₄^2-?

 

[samy4408]

the problem is that doesn't really match the definition , we don't see clearly the exchange of electrons .
In the conversion of cl to cl- it is clear that it is a reduction we see that the cl accept the electron , but in the case of converting SO2 to SO3 it is not as simple as the first example .

 

[samy4408]

Have you learned about redox potential? Redox (reduction/oxidation) is "all about electrons", which is a way to understand what you are asking.

Maybe this will help, if it is too advanced we can help you find something better.
https://www.sciencedirect.com/topics/earth-and-planetary-sciences/redox-potential

So it is all about comparing the redox potential between the two compounds (when the reaction is not simply the exchange of electron ).

 

[DrJohn]

So it is all about comparing the redox potential between the two compounds (when the reaction is not simply the exchange of electron ).

He's talking about examples like CH3CH2CH3 reacting to form CH3CH=CH2 and similar examples. Or CH3CH=CH2 reacting to form CH3CHClCH3. Or hydrolysis reactions where water is added across a double bond. Obvious things like an alcohol oxidising to a carboxylic acid are easier to understand as oxidation.

The answer is that in Organic chemistry it is often simply addition of oxygen = oxidation, and addition of hydrogen is reduction. It can be a bit tricky in Organic Chemistry to rationalise the standard add electrons / remove electrons concept because it almost never looks like that. Redox potentials don't get used in organic chemistry.

 

[samy4408]

thanks a lot !

 

[Fig Neutron]

For my organic chemistry class, we defined oxidation and reduction this way:

Oxidation is the addition of O/O₂, addition of X₂ (halogens), or loss of H₂.

Reduction is the addition of H₂/H^-, loss of O/O₂, or loss of X₂.

I also found it useful to think of oxidation as the conversion of a C-H bond to a C-O bond.
I am not sure if this answers your question, but I hope it is helpful.

 

[samy4408]

For my organic chemistry class, we defined oxidation and reduction this way:

Oxidation is the addition of O/O₂, addition of X₂ (halogens), or loss of H₂.

Reduction is the addition of H₂/H^-, loss of O/O₂, or loss of X₂.

I also found it useful to think of oxidation as the conversion of a C-H bond to a C-O bond.
I am not sure if this answers your question, but I hope it is helpful.

thanks a lot !

 

[DrJohn]

For my organic chemistry class, we defined oxidation and reduction this way:

Oxidation is the addition of O/O₂, addition of X₂ (halogens), or loss of H₂.

Reduction is the addition of H₂/H^-, loss of O/O₂, or loss of X₂.

I also found it useful to think of oxidation as the conversion of a C-H bond to a C-O bond.
I am not sure if this answers your question, but I hope it is helpful.

This is probably a better answer than my earlier one. As I'm an Inorganic Chemist / NMR Spectroscopist, I was digging into my memory for a simple answer and forgot the extras included in the above.

 

[HAYAO]

I'm not sure if I understand the OP correctly, but "oxidation/reduction of a compound" implies that there is a certain atom within that compound that changes its oxidation number. For example, when people say "oxidize CH3CHO into CH3COOH", they are actually referring to the carbon atom of the carbonyl group where its oxidation number changes from +2 to +3 during the reaction.
A more complicated case in organic chemistry is oxidation/reduction of a group of atom within the compound where aromaticity is involved. For example, you can oxidize benzene into benzene radical cation, and you may ask which of the six carbon atom has changed its oxidation number. Well, it's not an atom, but atoms because the orbital involved in the loss of an electron is the aromatic part of benzene, which is delocalized throughout the six carbon atoms. In this case, you can treat the aromatic part of benzene as if it was acting like a single atom (I admit this might not be the proper way to think about it, but for the sake of discussion, it's easier to understand).

Does this answer your question?

Redox potentials don't get used in organic chemistry.

That's not necessarily true. We do use redox potential in organic chemistry, especially when it comes to catalysts. I mean if it was true, we won't be able to understand photosynthesis.