Sciencemadness Discussion Board

Propadienylbenzene?

Rich_Insane - 16-1-2011 at 15:42

Ok, just a quick question.

So suppose you have a route to propadienyl bezene. I have read that propadiene (the simplest allene) exists in equilibrium with the alkyne, the alkyne being favored (K = 0.1 at 5 C). However, benzene is an aromatic system and stabilizes stuff like that (Forgive me, I have not gone through a full year of O Chem, and won't be until I graduate from HS). So if you have propadienylbenzene (double bonds between C1, C2 and C2, C3 on the sidechain), will it also form the propyne, or will it be stable enough to form more of the diene? How could one tip the equillibrium to the alkyne or diene side in this case then?

ScienceSquirrel - 16-1-2011 at 17:22

Actually the product Ph - allene is favoured over Benzylacetylene or Methyl phenyl acetylene under basic conditions.
Treat either of them with base and you will end up wth Ph allene as it has the least acidic protons.
it is a black glop system though as condensation will occur to make tars under most conditions ! :-)