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?