Substitution and bond strength/energy

[CATSandKILOS]

Hey guys,

Question from TBR chp1 review questions passage 1.4...

The greatest amount of energy is released by the oxidative cleavage of an alkene is... Unsubstituted.

Now I got the answer right because I thought well the less substituted the carbon the stronger it is and more energy required to break it.

I'm not sure if that's the right thought process or if in mixing things up. The explanation is what confused me: a less stable reactant yields a greater amount if heat upon reaction.

So is it the more substituted the carbon, the less stable? Is it still stronger than a tri substituted? Or is the more substituted more stable and stronger?

Ugh I'm confusing myself! Thanks

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[CATSandKILOS]

Anyone?

 

[MedHopeful20134]

Least substituted alkene would be unstable as compared to substituted alkenes.
Unstable species are higher in energy and hence when they react, they will release a greater amount of energy (in the process becoming more stable).
Hope that helps.

 

[CATSandKILOS]

Least substituted alkene would be unstable as compared to substituted alkenes.
Unstable species are higher in energy and hence when they react, they will release a greater amount of energy (in the process becoming more stable).
Hope that helps.

Thanks! So would this mean a substituted alkene is stronger than an unsubstituted alkene?

 

[justadream]

@Kate2

If by "stronger" you mean harder to break apart, then yes I think so.

However, for non-alkenes (as in, alkanes), I believe LESS substitution = stronger bond.

See TBR Ochem Book I page 11.

 

[CATSandKILOS]

@Kate2

If by "stronger" you mean harder to break apart, then yes I think so.

However, for non-alkenes (as in, alkanes), I believe LESS substitution = stronger bond.

See TBR Ochem Book I page 11.

I'll read that page. I meant stronger as in stronger bond.

 

[The Brown Knight]

I couldn't find the corresponding passage, but I'm guessing they also said oxidative cleavage is exothermic; even if they didn't, I would expect this to be true as electrons go from less electronegative substance (alkene) to more electronegative (oxygen).
The more substituted an alkene, the stabler it is. So an unsubstituted alkene should be higher in energy than a substituted one and will release more energy in ozonolysis (this is of course assuming that the ozonlysis products of different alkenes are similar in energy)