# Ring expansion from a given cyclic carbocation

How will the cyclobutane ring behave in the case of cyclobutylmethylium (cyclobutylmethyl cation)?

I initially thought there would be ring expansion to a five membered ring so that there may be less angle strain and a secondary carbocation instead of a primary one. But I have also been told that there will be ring contraction for stability purposes. I would be highly obliged if someone could explain the mechanism involved here.

• – Loong Apr 29 '15 at 14:44

• What would you think is more stable from the species $\ce{C4H7+}$, the cyclopropylmethylium (that you drew) or the methylcyclopropan-1-ylium? I tend to think the latter, but I am absolutely not certain. – Martin - マーチン Apr 30 '15 at 6:51