# Electrophilic addition on cyclopropane using sunlight

I encountered a weird question in an exam. The statement says that instead of radical substitution, cyclopropane undergoes electrophilic addition reaction in sunlight.

I know that all saturated compounds give substitution reactions in sunlight but the answer key states that electrophilic addition takes place.

I couldn't find any source to prove this. Any help with an explanation and a verified source would be appreciated.

• – Tan Yong Boon Jul 18 '20 at 4:14

Cyclopropane suffers badly from ring strain. The bond angles in the ring are 60° rather than the normal ~109.5° when carbon makes four single bonds. In the absence of light, when in contact with $$Cl_2$$ or $$Br_2$$ the ring will break and addition occur.

In sunlight, both the expected substitution reactions and the addition reaction will occur.

Can't find the reference I thought I remembered, but here's a site or two discussing it:

https://www.chemguide.co.uk/organicprops/alkanes/halogenation.html

https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_General_Chemistry_(Petrucci_et_al.)/27%3A_Reactions_of_Organic_Compounds/27.07%3A_Reactions_of_Alkanes