Would one get 1-(1-chloroethyl)-1-methylcyclobutane?

I am not sure if the driving force identification is correct? Is my going from a 2° to a 3° carbocation correct? Does anyone have any tips for knowing when to look out for rearrangements?


1 Answer 1


I think the solvolysis would involve rearrangement to the cyclopentyl carbocation as indicated in the figure below. The driving force for the rearrangement is two-fold

  1. without rearrangement, the cyclobutyl compound would generate a secondary carbocation; with rearrangement a more stable tertiary carbocation is generated instead
  2. release of strain as the 4-membered ring opens to a 5-membered ring

enter image description here

The tertiary cyclopentyl carbocation ultimately captures a solvent molecule as indicated.

  • $\begingroup$ the + charge goes onto the cyclic ring. Does that destabilize the ring more than having a 4-membered ring? $\endgroup$
    – yolo123
    Nov 1, 2014 at 20:45
  • $\begingroup$ An $\ce{sp^2}$ carbon would like to be around 120 degrees; that angle is not destabilizing in 5-membered or larger rings. $\endgroup$
    – ron
    Nov 1, 2014 at 20:53

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