Radical Halogenation

Question 1

What is a carbon radical?

Answer 1

It is a neutral electron deficient carbon sepecies and is a common intermediate. The geometry of a carbon radical is planar as its hybridization is sp2.

Question 2

What is the motor of a radical halogenation reaction?

Answer 2

On the arrow you write light (hv) because it allows dihalides to dissociate as radicals

Question 3

What is the reaction mechanism of a radical halogenation?

Answer 3

In the presence of light, a dihalide dissociate to form two halide radicals.
These radicals are VERY reactive. So they abstract the hydrogen from an alkane and forms a X-H sigma bond. Consequently a carbon radical is left as intermediate. The new carbon radical attacks X2 and forms C-X sigma bonds and another halide radical.

Question 4

When does a radical halogenation reaction stop?

Answer 4

As long as there are sp3 C-H bonds and X2 it can be halogenated in light

Question 5

Determine the outcomes of a radical halogenation reaction

Answer 5

The outcomes can be sketched on a reaction coordinate diagram. The radical intermediate that is the most stable will be favored.
Radicals are ranked from most stable to least stable as follows: conjugated radical, 3deg, 2deg, 1deg with hyperconjugation every time.

Question 6

What are the key features of a radical halogenation reaction?

Answer 6

1- either side attack: X2 can attack Carbon radical from top or bottom
2- scrambling of configuration : new sp3 atoms are racemic 50/50(if chiral)
3- halogenation at most substituted C-H it is regioselective to produce the most stable radical intermediate
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