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.


1 Answer 1


It should say "in addition to" rather than "instead of".

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:




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