Epoxide with ethanol under acidic condition adds to where??

[SheepAndOwl]

Chad's video says the priority is 3' > 1' > 2' but destroyer just says it adds to most substituted (3' > 2' > 1'). Can anyone clarify this??

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[DAT Destroyer]

.This is a great question that I see many professors debate endlessly . Here is a nice rule of thumb.....If in Acid,,,,,add to the MOST substituted carbon. This works great....since in the transition state we are developing what I call a quasi carbocation intermediate,,,,, In base, the argument is different, it is purely steric,,,,,thus in BASE....hit the less substituted carbon. Now comes the problem......what If the epoxide has only 1 substituent ? Read the David Klein book or John McMurray book, they say.....one thing...read the Maitland Jones book or Xiaoping Sun Advanced Organic Chem book, they say another. Who wins ? LOL,,,,I have done the reaction for about 32 years,,,,,and guess what ? I found MIXED results......because it is honestly hard to predict.. It depends on factors such as solvent, and nucleophile strength. HOWEVER for the DAT,,,,OAT...MCAT.....use the rule that in acid.....we hit the more substituted carbon......in base,,,,hit the less substituted carbon. This will be your best guide,,,,Through years of doing this....I tend to agree more with Dr. Sun and Dr, Maitland Jones, Professor Emeritus of Princeton who has done this chemistry long before Klein was even born !!!! It is my feeling that the DAT will give you a question on an epoxide that is clear cut, and not one that is open to debate or needs empirical analysis.

Hope this helps......
Dr. Jim Romano....