  New data on proton and neutron single-particle energies $E_{nlj}$ of Si
isotopes with neutron number $N$ from 12 to 28 as well as occupation
probabilities $N_{nlj}$ of single particle states of stable isotopes
$^{28,30}$Si near the Fermi energy were obtained by the joint evaluation of the
stripping and pick-up reaction data and excited state decay schemes of
neighboring nuclei. The evaluated data indicate following features of
single-particle structure evolution: persistence of $Z = 14$ subshell closure
with $N$ increase, the new magicity of the number $N = 16$, and the
conservation of the magic properties of the number $N = 20$ in Si isotopic
chain. The features were described by the dispersive optical model. The
calculation also predicts the weakening of $N = 28$ shell closure and
demonstrates evolution of bubble-like structure of the proton density
distributions in neutron-rich Si isotopes.
