2010 final Q7B naming cis/trans

[katia makhovik 4F]

The question asks to name the molecule. It shows 2-butenoic acid, but the name says trans- at the beginning. Why is that so? How do we know that we need to add a trans or a cis when naming the molecule?

[Neil DSilva 1L]

Anytime there is a possibility of the molecule having an isomer, you have to indicate if it's cis- or trans-.

Notice that there are two ways you can draw the molecule if cis- or trans- isn't specified (you could draw the fourth carbon going up from the third carbon and it would have the same molecular formula as the molecule drawn in the practice final, but it would be a different molecule).

I think, in general, anytime there's a double bond that isn't a part of a functional group or if you have a cycloalkane, you should be considering the possibility that the molecule might have an isomer and cis- or trans- is required in the naming.

[Chem_Mod]

Neil is correct. You should be able to look at structures and determine if isomers are possible.