Can an article having spin be seen as spinless in a properly choosen frame of reference?

Question

Lets take two-atomic molecule that has spin while the both atoms have zero spin. Can we choose a frame of reference where this molecule has no spin?

Answer 1

Spin is precisely the number that tells you in which representation of the rotation group $\mathrm{SO}(3)$ (non-relativistic) or Lorentz group $\mathrm{SO}(1,3)$ (relativistic) a quantum state transforms. As these groups are precisely the transformations between reference frames (aside from the boring translations), spin is an invariant under change of reference frame.