  The problem of the spin states corresponding to the solutions of Dirac
equation is studied. In particular, the three sets of the eigenfunctions of
Dirac equation are obtained. In each set the wavefunction is at the same time
the eigenfunction of one of the three spin operators, which do not commute with
each other, but do commute with the Dirac Hamiltonian. This means that the
eigenfunctions of Dirac equation describe three independent spin states. The
energy spectrum is calculated for each of these sets for the case of
quasi-two-dimensional electrons in a quantum well. It is shown that the
standard Rashba spin-orbit interaction takes place in one of such states only.
In another one this interaction is not formed at all, and for the third one it
leads to the band spectrum which is anisotropic in the plane domain of the
propagation of a free electron and is different from the isotropic spectrum of
Rashba type.
