[o0CY0o]

Why can we say that the oxidation state of aldehyde is higher than that of ester?

I've been working of the C-O and C-H bond ratio and finds that ester has a higher C-O:C-H
Isn't it right to say that ester has a higher oxidation state?

[azmanam]

esters are higher o.s. than aldehydes.  you need to do a reduction (DIBAL) to convert an ester into an aldehyde.

[Squirmy]

Isn't it right to say that ester has a higher oxidation state?

Yes, a C-O:C-H ratio would give you their relative oxidation states.

There's a more general approach that's an extension of oxidation states you from Gen chem [-H --> +1; =O --> -2; -O --> -1; -X (-Cl, -F, -Br, -I) --> -1]. There's a notable exception to these rules...when two of the same elements are bonded to each other. For example, in H₂, each hydrogen as an oxidation state of 0.

Applying this to methane (CH₄), the carbon has an oxidation state of -4, because each H is +1. For ethane (CH₃CH₃), each carbon has an oxidation state of -3, (3 bonds to H = +3, 1 bond to another C = no effect).

In more complicated structures, you can have multiple carbons with different groups attached...you can assign oxidation state to each carbon.

[sjb]

esters are higher o.s. than aldehydes.  you need to do a reduction (DIBAL) to convert an ester into an aldehyde.

Sure, the acid part of the ester is in a higher oxidation state, but are esters in general?

I hope we agree that addition of water does not affect oxidation state, so we can have RCO₂R'  RCO₂H + R'OH giving no change overall. Similarly, the Cannizzaro reaction is 2 RCHO  RCO₂H + ROH. So where's the fallacy?

[azmanam]

Sure, the acid part of the ester is in a higher oxidation state, but are esters in general?

yes.  esters are at the 'acid' oxidation state.  the 'acid' oxidation state includes acids, carboxylates, amides, esters, anhydrides, and acid chlorides.  They're all at the same oxidation state.

Cannizzaro is a net neutral reaction, but one of the carbons is oxidized while another is reduced.  I suppose all redox reactions are net neutral, then.  one of the steps involves the transfer of hydride to a carbonyl center.  The hydride source is atypical, but in that sense it's like the MPV/Oppenauer process.  Are you suggesting that's not a redox reaction?  It's not a fallacy.  For all redox reactions something gets oxidized and something else gets reduced.  Cannizzaro and MPV are both examples where both the oxidant and the reductant are organic molecules.