# If 360 rotation is possible, How Molecule exist with particular Configuration

I Have confusion, If we talk about Ethane Molecule, we can get different conformations. For ethane, the eclipsed and staggered are freely inter-convertible and in between these two extreme conformations lie infinite number of conformations where the dihedral angle may be 1degree or 2 degree or 10 degree etc. Thus, a slight change in the overall 3-D orientation in space results in a new conformer.

Now Coming to question, If rotation around single Bond is So free, Why Glucose Exist as (+)-Glucose, Why not C4 carbon get rotated simply by 180 and Get converted to glactose (as its rotation is free)?

What I am missing here?

• You are totally missing the point. Re read the answer, made some draw, buid a little model of few molecule – Alchimista Nov 18 '17 at 9:08
• Alright, I get that. I was thinking on the basis of Fisher projection. Thank you. – aman Nov 18 '17 at 13:18
• chemistry.stackexchange.com/questions/59124/… – Mithoron Nov 18 '17 at 17:47
• Geometric isomerism exists exactly because rotation can be blocked. – Mithoron Nov 18 '17 at 17:48

I think you are confused between arrangement of different groups around carbon ($C$) and free rotation about $\ce{C-C}$.
In conformers, the orientation of groups in space does not change, but only rotation about $\ce{C-C}$ occurs. Note that this will never change the spatial configuration of groups around any carbon!
So + glucose will not get converted to any other optical isomer on changing conformations about any $\ce {C-C}$.