1. Phenolic antioxidation Go to Slide Show mode and click the big red button

2. Low energy, low reactivity High energy, high reactivity R-H Allylic hydrogen in triglyceride

3. Low energy, low reactivity High energy, high reactivity R. + H.

4. Low energy, low reactivity High energy, high reactivity R. O2O2

5. Low energy, low reactivity High energy, high reactivity RO2.O2. Hydroperoxyl radical

6. Low energy, low reactivity High energy, high reactivity RO2.O2. R-H Allylic hydrogen in triglyceride

7. Low energy, low reactivity High energy, high reactivity ROOH Hydroperoxide, decomposes to form smelly products R. Returns to propagation, continues cycle

8. But……. Look what happens if we have a phenolic antioxidant around at the point where the hydroperoxyl radical would normally react with another molecule of lipid, RH

9. Low energy, low reactivity High energy, high reactivity RO2.O2. OH HO Hydroperoxyl radical

10. Low energy, low reactivity High energy, high reactivity O. HO ROOH This radical is low energy, does not continue propagation reaction

11. Compare…... The situation with and without a phenolic antioxidant

12. Low energy, low reactivity High energy, high reactivity O. HO This radical is low energy, does not continue propagation reaction ROOH Decomposes to form smelly products R. Returns to propagation, continues cycle WithoutWith ROOH Decomposes to form smelly products

13. Why? The question still remains why the ROO. (or the R.) radical would react with the phenolic antioxidant rather than another molecule of RH The answer lies in the concept of reaction activation energies

14. ROO. or R. RH phenolic Increasing energy

15. So….. The reason phenolic compounds are antioxidants (that is, they induce early termination) is The activation energies (energy necessary to do the reaction) are lower, and The product (phenolics and quinones) energies are lower