I have been wondering on this for quite a while. Consider aliphatic monoaldehydes. If I oxidize them, we get corresponding monocarboxylic acids. We can use certain oxidizing agents to perform the reaction.

For all the possible aliphatic aldehydes, it involves breaking a $\ce{C-H}$, and the formation of the $\ce{C-O}$ and a $\ce{O-H}$. I did calculations and got the enthalpy change for such a process to be $\pu{412kJ/mol}$.

My main motive is to find the electrode potential for the process. Unfortunately, I cannot determine the entropy here, although I don't think the side chain would matter much.

Here's my question. Does the oxidation for all the aliphatic monoaldehydes to carboxylic acids have the same value of electrode potential? In all the cases, it's the same bonds broken and same bonds formed, so I cannot see why the electrode potential should drastically vary for different aldehydes.

My apologies, I was unable to find a $\Delta\text{G}$ value table for such processes.


My answer to your main question is no.

Firstly, you are simplifying the process of oxidation of the monoaldehyde. The mechanisms for oxidation depending on the oxidising agent used, although they are generally the same (Refer to link). By considering only these 3 bond formation/cleavage events, you are not looking at this process in totality.

Secondly, the side chain does matter as it would affect the bond energies of the bonds that are broken and formed. Different side chains may give the aldehyde different steric strains etc. Depending on whether it is more electron-withdrawing or electron-donating, it can severely influence the bonds on the carboxyl group.

Due to the variations in oxidising agent, medium of reaction and side group of aldehyde, the oxidation of different monoaldehydes to carboxylic acids would have a different value of electrode potential as these factors would affect the feasibility and ease of oxidation.

Oxidation using chromic (VI) species:



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