From experience when working with dcm, distilling, refluxing etc...etc Swim highly recommend that you use ice cold water in your condenser, get yourself a nice aqurium pump, attach it to the condenser and make a reseviour(pardon my spelling) then run both hoses to the water, get plenty of ice, and make a trap at the top of your condenser, generally Swim has a tube attached which goes into a beaker with ice cold water that way most of the dcm vapors say out of the air and away from your lungs.
DCM exposure will give you a headache like none other and breathing too much of it will knock you off your feet.
Anyway, please becareful, this thread is scary, its a good thing nothing bad happened. As for your yields I am sure you did get product however there might have been lots of side reactions taking place.
Generally swim keeps check on his reaction during the additoin process.
Another tip, if you add your performic solution to fast to the isoalkene, and you feel you're about make a nice acidic water cannon, turn your stirrer off for a little while
or at least slow it down, it will slow down the reaction and you won't have to deal with the clean up of acid everwhere in which case baking soda is your best friends for acid spills.
Don't give up your almost there.
Doc. I recommend boiling water to remove the tar that was formed, next time you run your isomerization try to keep the temp. around 120-140C and you won't have much formed.
What you can do is post isomerization is vacuum filter the oil and remove some of that KOH before you go ahead and do your distillation.