# Mechanism for the ring contraction

In this reaction I am unable to understand its mechanism. How the peroxide HCCL3 is causing the ring contraction. I know that the 8 member ring is unstable due to strain and hence it will try to contract. But I am not able to initiate the mechanism due to reagents present. Please can someone explain me how the contraction of 8 members ring to 2 five member ring is taking place?

• Peroxide is acting as a source of radicals. – Waylander May 16 '20 at 6:55
• @Waylander what will be the first step? – Zenix May 16 '20 at 8:06
• Creation of the CCl3 radical and addition to one of the double bonds. See this for a summary chem.libretexts.org/Bookshelves/Organic_Chemistry/… – Waylander May 16 '20 at 9:05
• @Zenix: This is a radical reaction. Peroxide initiate the radical formation by abstracting a hydrogen from $\ce{HCCl3}$ to form $\ce{^.CCl3}$ radical, which attacks one of the double bond first, and rearrangement happens there after to give $2^\circ$ carbon radical. It abstract hydrogen from another $\ce{HCCl3}$ to give the product and another $\ce{^.CCl3}$ radical, so reaction progress to the end. – Mathew Mahindaratne May 16 '20 at 9:12

As has already been said in the comments, this is a free radical-based reaction. The peroxide $$\ce{R1-O-O-R2}$$ acts as a radical initiator( where $$\ce{R1}$$ and $$\ce{R2}$$ represent alkyl groups). These peroxide radicals generate $$\ce{^.CCl3}$$ which attacks the double bond and completes the reaction as shown.
An important point to note is that $$\ce{^.CCl3}$$ is regenerated at the end of the reaction, so it can be described as a catalytic intermediate for this mechanism