DAT Destroyer 2015 Orgo #92

[nickh]

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Hey guys,

Sorry with all the questions, in the last 2 week crunch time mode😛 Anyways, for the choice c, the answer keys says I replaced Cl in a polar aprotic solvent. I thought in a such solvent, Cl would be the better nucleophile, so then shouldn't there be no reaction, because I wouldn't be able to replace Cl?

Hope your studying's going well!

 

[DAT Destroyer]

Hey guys,

Sorry with all the questions, in the last 2 week crunch time mode😛 Anyways, for the choice c, the answer keys says I replaced Cl in a polar aprotic solvent. I thought in a such solvent, Cl would be the better nucleophile, so then shouldn't there be no reaction, because I wouldn't be able to replace Cl?

Hope your studying's going well!

In a polar aprotic solvent iodine is still a reasonably good nucleophile. NaI in acetone works very nicely when doing SN2 reactions. We call it the Finkelstein reaction.

Hope this helps..Keep up the great work!

 

[Denizen]

To follow up on this old post, I don't understand why choice (e) would not yield competing SN1 and E1 reactions (if an E1 were to occur, this would be a second correct choice). How would I know that E1 wouldn't happen here?

 

[workofshart]

I looked into this because I was curious too and the only thing I could find is that since it is low temp SN1 is favored... My guess is that being in an aqueous solution has something to do with it as well but I'm not sure what. Hopefully someone else responds.

 

[tommyngu]

To add to what orgoman22 replied:
Here the the rules for nucleophilicity that I've compiled:
For comparing atoms within the same period (whether charged or uncharged), nucleophilicity follows basicity (increases to the left).

For comparing uncharged/neutral atoms within the same group, nucleophilicity follows size (increases going down).
For comparing charged atoms within the same group, it depends on the solvent.
For charged atoms in protic solvent, nucleophilicity follows size (increases going down)
For charged atoms in aprotic solvent, nucleophilicity is follows basicity (increases going up)

Since the question in the OP seems to compare Cl vs I in a polar aprotic solvent, I would be the better nucleophile.