Structural / displayed formulae

Student question:

When the question says “give the structure of each isomer” and gives us 4 boxes for answers, the mark scheme wrote the structural formula. Will it be wrong to if we draw the displayed formula.

I’ve had a lot of queries about this. I can only give a view on this – meaning my view may be wrong – but if the question said give the structural FORMULA then you simply must give the structural formula.

If – as in the case above – it says just “structure” and not structural formula, then I would say the displayed formula should get marks, because by only asking for the ‘structure’  it seems the questioner is most interested in the connectivity of the atoms – in the longest chain – especially given the question is asking about isomers. That’s how I see it.

A displayed formula, or hybrid of displayed and structural formula, is not given in the mark scheme (e.g. for 9701_s15_qp_22.pdf Q4) but I think that’s just for “workability” reasons, as it’s very hard for a ms to list every single allowable possibility.. The examiners report makes no mention of an issue with displayed formula so I guess the displayed formula was accepted.


A structural formula Shows each proceeding carbon in the longest chain (the ‘root’ of the molecule, used in naming the molecule) and the “side” atoms or side groups on that carbon before listing the next longest chain carbon and its “side” atoms or side groups etc etc etc, until all C’s in the longest chain have been listed…….


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