In a question I saw comparing the reactivity (to addition reactions) of cyclopropane, cyclobutane and cyclopentane, it was said that cyclopropane was most prone to addition reactions.

Ring strain does make it prone to reactions, but how can addition reactions make it any more stable?

In that context, how can you compare the three?

  • $\begingroup$ A cycloalkane ring has just one degree of unsaturation. An addition reaction would remove that unsaturation, to give a saturated product. A saturated product can never be a ring. $\endgroup$ – Aumkaar Pranav Mar 26 at 5:27

You're absolutely right: cyclopropane's maximum ring strain makes it highly prone to addition reactions. Keep the following definition in mind:

An addition reaction, in organic chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one (the adduct).

In your case:

enter image description here

Thus, it breaks down the ring into a straight chain, which makes the low stability of the ring a clear contributing factor to the reaction.

References: Cyclopropane, wikipedia|| Addition reactions, wikipedia

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  • $\begingroup$ So there aren't any cases where addition occurs without the ring being broken, right? $\endgroup$ – Harry Holmes Mar 26 at 3:10
  • 1
    $\begingroup$ @Harry Holmes Yes, either a ring or a double bond would need to be broken. $\endgroup$ – Nikhil Anand Mar 26 at 4:43
  • $\begingroup$ Oh, okay. Thanks. $\endgroup$ – Harry Holmes Mar 26 at 4:49

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