A homework question I was given asked me to identify the most stable carbocation between these 4. I was able to narrow it down to either the trifluoromethylcyclohexane carbocation or the methoxycyclohexane carbocation, but I’m not sure which between the two of them.
My gut feeling is that the methoxycyclohexane is more stable because of its contributing resonance structures, but I’m not sure if that trumps the hyperconjugation that the fluorine atoms provide. Any insight would be appreciated!
The fact that the methoxycyclohexane carbocation is resonance stabilized greatly increases its stability over the the trifluoromethylcyclohexane carbocation.
The same power of oxygen’s ability to donate electrons can be seen in its effects on benzene rings. Both $\ce{-OH}$ and $\ce{-OR}$ groups are strongly activating groups, while $\ce{-CF3}$ is a ring deactivating group, meaning it actually pulls electrons from the benzene ring. This further shows that the methoxycyclohexane carbocation is the most stable of the 4.
