[gralla55]

What would be the best reagent for this substitution reaction?

   1.  D2, Pt
   2. D2SO4, D2O
   3. i. Mg, Et2O, ii. D2O
   4. NaOD, D2O
   5. D2O, acetone


I don't think two steps are necessary, which excludes #3. Also, NaOD is a strong base, which I don't think works well with the halogen, which excludes #4. And it makes me think #2 has to be correct since it has the strong acid, but I'm not sure... any help? Thanks!

[Doc Oc]

You should re-consider one of the answers you struck down.

[gralla55]

Hmm... Mg reacts with Br?

[Doc Oc]

Well, that's something you're going to have to figure out.  Think about the reactions this way, deuterium (D) is just like hydrogen.  So replace the D's with H's and then see if you can make more sense of what would happen.

[gralla55]

Yes, I knew about the deuterium-thing. I just don't see how the base which has a negative charge would react with the also negatively charged Br. Mg at least has a positive charge, but I admit I don't see how the rest of the reaction would unfold if 3 is the right answer. Anything I'm missing? Thanks for helping.

[g-bones]

the magnesium you will be considering is not positively charged when it enters the reaction.  what types of reactions does Mg(0) undergo with akyl halides?  once you figure out the resulting intermediate it is important to think of its properties and how that will interact with D2O.  keep trying, youll get there.