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Which of the following Fischer projections is different from the other?

Just by looking at the R-S configuration, figure C is the odd one out. But when I look at D I see that both methyl and hydrogen are below the plane while in other diagrams it hydroxyl group and hydrogen, meaning howsoever you orient both C and D by rotation you will never be able to get the same spatial arrangement as A and B. I am confused by this, my TA says the answer should be opt C because of the configuration and I haven't talked to him about this approach.

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If you try to redraw the structure of compound D you will obtain a spatial arrangement that is only in apparence different from structure of A and B.
With a rotation of 120° around the C-H bond you will obtain a spatial arrangement that is identical to the others.

Which of the following Fischer projections is different from the other?

The final answer is C because it has a opposite configuration from the others:
C = R
A,B,D = S

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    $\begingroup$ Any pairwise swap changes the stereochemistry, so an even number of swaps retains the stereochemistry. This is the rule to figure it out on paper. Of course building the models in 3D is much better for a deeper understanding and believing the answer. $\endgroup$
    – Karsten
    Commented Aug 22, 2023 at 7:19

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