Saturated and Unsaturated fatty acids

[Hemichordate]

Which one, saturated or unsaturated, is the more stable one? Does that trend hold true for all compounds as well?

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[RogueUnicorn]

"stability" is not exactly a rigorious term, are we speaking in terms of heat release upon combustion?

 

[t1me]

I would reason like this:

If by more stable you mean less reactive, then saturated compounds are more stable. The unsaturation creates electron density between carbons, which makes the bond more reactive. It also makes the hydrogens attached to the sp2 carbons more acidic/reactive.

Not sure if this is correct though.

 

[Hemichordate]

"stability" is not exactly a rigorious term, are we speaking in terms of heat release upon combustion?

Yes, I meant heat released upon combustion.

 

[RogueUnicorn]

saturated fats will release more heat, i believe, because they are at a more reduced state.

 

[Isoprop]

Also, when you create a C=C double bond, you need to break 2 sigma bonds. So that also tells you that saturated holds more energy.

 

[PiBond]

i think of it this way: the more reduced something is, the more it can be oxidized, and thus the more heat will be released upon its complete oxidation to CO2. this is why carbohydrates have a lower energy content than fatty acids. carbohydrates have several oxygens and unsaturation units (in the form of rings or double bonds) while a saturated fatty acid is composed of mainly hydrocarbons.

remember that: heat of a reaction = energy of bonds broken - energy of bonds formed. the CO2 we form upon complete oxidation of carbon has much stronger bonds than a simple alkane sigma bond. thus we get a negative value and this explains why double bonds (unsaturation units) will release less energy upon oxidation--it takes more energy to break a double bond and thus we won't have as much energy released upon oxidation