Orgo Problem from Chad's

[Syntav]

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Why wouldn't the first set of reagents work? Wouldn't NaOCH3 undergo an E2 reaction with the alcohol to produce an alkene?

 

[shonster460]

It's been a while since I took the DAT but I believe the E2 does not work because the hydroxyl group by itself is a poor leaving group. It needs a proton to be a good leaving group, which is what you see in the correct answer.

 

[10617573]

E2 reactions happen with a good leaving group (Br,Cl,I) and an anti coplanar Hydrogen, the first set of reagents like Shonster said would not protonate the Hydroxyl group keeping it as a bad leaving group and not letting it do the E2 reaction. The H2SO4 in the correct answer protonates the Hydroxyl group making an hydronium Ion, H3O+ which is a very good leaving group and then the HSO4- takes from the anti coplanar hydrogen forming the alkene and pushing off the hydronium ion. Now that the alkene is formed the rest of the reagents react and you get the hydroxyl group following markov's rule. Hopefully this is right or I'm in trouble for the my upcoming test day 😀

 

[Syntav]

thanks guys! and good luck 106!