Question

Question: In cells, vitamin C exists largely as its conjugate base X. X is an antioxidant because radicals formed in oxidation processes abstract the labeled H atom, forming a new radical that haltsoxidation. Draw the structure of the radical formed by H abstraction, and explain why this Hatom is most easily removed.

Short answer

Answer

The radical formed by proton abstraction is given below:

The labeled hydrogen atom can be easily removed as it leads to the formation of a stable allylic radical.

Step-by-step solution

Free Radicals

Free radicals are molecules comprising an unpaired electron.These species possess great reactivity because of this unpaired electron. They can be created by homolytic cleavage.

Hydrogen atom abstraction

Hydrogen atom abstraction is also known as hydrogen atom transfer. It is a process in which the hydrogen free radical is detached from a particular species as per the equation below:

$X+H-Y\to X-H+Y$

 Step 3:Structure of the radical formed by proton abstraction

The structure of the radical formed by the abstraction of labeled H is shown as:

Radical formed by proton abstraction

The allylic hydrogen atoms can be easily abstracted as it leads to the formation of allylic radical which is resonance stabilized. The order of the increasing stability of free radicals can be given as:

1⁰<2⁰<3⁰<allylic

Hence, the hydrogen atom can be easily removed as it leads to the formation of stable allylic radical.