In this lecture, I am learning to form epoxides from the intramolecular version of Williamson Ether synthesis. During that, the professor says the ring formation is favored when ring is 3/5/6-membered, and not favored in 4/>6-membered. I tried to think of: smaller bond angle increases ring strain, but this does not explain why 3-membered ring is favored.

I checked the answer to this question.

Why are 7-membered rings less likely to form than 5- and 6- membered rings?

  1. It seems that 3-membered rings have a very positive ΔG, how come it is favorable?
  2. In the last graph of the answer, overall rate of formation of 4 & 6-membered rings seems around the same (log k(intra)), which I really want to know the explanation of that. In general, what membered rings are actually favored?

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