[DannyBoi]

I submitted a homework question online and this is the result:



Can it be clarified what I was missing?

[DannyBoi]

Could it have been the Hydrogens? I was under the assumption that they were implicit but maybe now I do remember my book displaying them to clarify the E/Z isomerism nomenclature. :S

[dunno260]

There is a 4th isomer I was able to come up with.  All of your answers are Z isomers and appear to be correct.  The only thing I can think of is that it wants the vinylic bromine (attached to the double bond) so your (Z)-1-bromo-2-butene structure is the one that its counting as wrong (though the geometry is Z).