not sure what they were alluding to, but my guess from first look was all the double bonds (represented by 2 lines parallel) on a single carbon, and those 2 double bonds being bent (i am not getting into sp carbon hybridisation, and specifically double double bond sp), but that is basically not possible (alost no amount of streic hinderance can do that).
Then what is?
not sure what they were alluding to, but my guess from first look was all the double bonds (represented by 2 lines parallel) on a single carbon, and those 2 double bonds being bent (i am not getting into sp carbon hybridisation, and specifically double double bond sp), but that is basically not possible (alost no amount of streic hinderance can do that).