Addition Of Alcohols To Alkenes With Acid
Description: Alkenes treated with acid in the presence of an alcohol (usually as solvent) form ethers.
This page is available to MOC Members only.
Sign up here for about 30 cents/ day!
Real-Life Example:
Org. Synth. 1940, 20, 81
DOI Link: 10.15227/orgsyn.020.0081
Click to Flip
can you explain the mechanism of the intramolecular reaction in example #4??
Sure. First step is that the alkene reacts with H+ to form C-H on the less substituted carbon, leaving behind a tertiary carbocation. This tertiary carbocation is 5 bonds away from the oxygen. 5 membered rings are nice and easy to form. So the oxygen lone pair attacks the carbocation generating a new 5- membered ring which is then deprotonated.
Intramolecular reactions are great exam questions.
During the final deprotonation step, does one have to consider the pKa’s of both the R-OH and the H+ in order to properly write out the mechanism?
I don’t think so. There’s often multiple species in solution that are competent to act as a base on a strong acid like protonated alcohol (pKa -3). I drew HSO4- here to complete the catalytic cycle but honestly it could be a number of different species. That’s why people often just like to write, “B” for generic base.