[pdffree]

Can anyone check out what i got?

[nj_bartel]

The second step should have the electrons from the oxide attacking the carbon attached to the bromine, with bromide eliminating.  Can't decipher what you drew.  And it's an intermediate, so you should have brackets around it.  That product's an epoxide, by the way.

[pdffree]

do you know why is  the  choise (amount  of base) very critical?

[azmanam]

what happens if you have excess base that is also a good nucleophile?

[pdffree]

reaction doesn't take place?/

[azmanam]

no... you'll still initially form the epoxide.

one of the biggest challenges in organic synthesis is finding reaction conditions that will perform the transformation you desire... and nothing else.

here, after you form the epoxide, there is another reaction that could happen if you have excess base that is a good nucleophile.  do you see what it could be?

[pdffree]

nope!

[azmanam]

flip forward a few pages in the epoxide chapter to the nucleophilic ring opening of epoxides and give that section a read.

imagine if you did the reaction you drew in the o.p. with excess NaOH.  What might happen after you form the epoxide?

[pdffree]

it reopens the epoxide! -

[azmanam]

right.  good.

so you need a non-nucleophilic base (LDA, maybe NaH), and just 1 equivalent.

see here for more general info:
http://www.chem.uky.edu/courses/che232/JEA/ln/4a.%20Ethers.pdf
http://depts.washington.edu/chemcrs/bulkdisk/chem238A_win05/notes_16_pt2.pdf

[pdffree]

and the mechanism is correct, right?

[azmanam]

Here's how I would draw it. 

Can the first part of this mechanism (the formation of the epoxide) be classified as an S_N2 reaction?  why or why not?

[pdffree]

Thanks a lot ! You guys r master in CHM