[qwerty]

In a dichlorocarbene addition to cyclohexene using a phase-transfer catalyst, why is it important to vigorously shake the mixture??

Also, which carbene (:CH2 or :CCl2) would be expected to be more reactive and why?

Thanks

[Mitch]

:CH₂ is more reactive because the chlorines help stabalize the carbene.

[GCT]

In a dichlorocarbene addition to cyclohexene using a phase-transfer catalyst, why is it important to vigorously shake the mixture??

Recall that a phase transfer reaction requires two phases, one is polar and the other nonpolar.  The catalyst Q+ has a both ionic and a non-polar motif.  The Q+ reacts with the nucleophile, N, through a rather weak bond and is transferred to the nonpolar phase in which the Q and N dissociates, leaving raw N to react with the specified reactant within the nonpolar phase.  Thus the point is to stir up the reaction by shaking it.

Also, which carbene (:CH2 or :CCl2) would be expected to be more reactive and why?

I would imagine that :CH2 would be more reactive, :CCl2 can donate electrons through delocalization (p-d) and thus stabilize the positive charge.

Thanks

[qwerty]

Thanks, but can you clarify what N and Q are?

[GCT]

N is the nucleophile and Q is the transfer catalyst.  You might want to review what phase transfer catalysts are all about as I'm a bit rusty on this topic.

[polly]

Since chlorine is very electronegative, wouldn't the :CCl2 be more reactive??

[Mitch]

Eventhough it is electronegative it can still inductively donate some of it's electron density into the vacant orbital of the carbene. I was told this by a carbene chemist that works for Guy Bertrand. Guy's one of the big shots in the field.

[polly]

i see...thanks