For molecules to be enantiomers, do the groups have to be non-superimposable mirror images even when rotated around C-C single bonds?

For example, if I rotate the Carbon-Carbon bond in **B** around 120 degree anti-clockwise, I would get the molecule shown in image **C**. **C** looks to me like a non-superimposable mirror image of **A**, hence **A** and **C** are enantiomers. 


However, as drawn, **A** and **B** do NOT seem to be mirror images.


Are **A** and **B** enantiomers considering what happens after a bond rotation?


[![enter image description here](https://i.stack.imgur.com/6JSsF.png)](https://i.stack.imgur.com/6JSsF.png)




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Note: ChemDoodle shows those red triangles saying "questionable stereochemistry". I'm not sure what is wrong but the molecules I drew may have some issues, but I think the question still holds.




Real molecules surely **do** rotate around their single C-C bonds all the time(\*). So yes, if two models can be superimposed after an internal rotation of such sort, this means they represent the same molecule, as is the case with your **B** and **C**.


This, BTW, is the reason why you should orient all substituents in a standard manner when drawing your [Fischer projections](https://en.wikipedia.org/wiki/Fischer_projection). Otherwise any molecule would have just too many variants, and you'll get bogged down in them. Think of rotating the upper group the third way (the first two being **B** and **C**). Think of rotating the lower group too...


Then again, I've rarely seen Fischer projections used for anything other than sugars. Typically people just determine the [absolute configuration](https://en.wikipedia.org/wiki/Absolute_configuration) (**R** or **S**) and go with that. It gives you a definitive answer, after all.




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(\*) That is, *most of them* do. When you have bulky substituents, rotation may pretty well get blocked, and then you may be able to separate the isomers that are (nominally) produced by this rotation - they are no longer equivalent. Look at [BINOL](https://en.wikipedia.org/wiki/1,1%27-Bi-2-naphthol) or [BINAP](https://en.wikipedia.org/wiki/BINAP), for example.


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