Recent studies of interaction cross sections, fragments momentum distributions combined with standard quantities such as mass and beta‐decay Q‐values reveal new dynamic change of shell structures. In particular, special attention is paid on neutron
halo nuclei in the p‐sd shell. In halo nuclei and other neutron rich nuclei, the 2s1/2 orbital shows irregular behavior. One such extreme case is the new neutron magic number N=16. The global behavior of 2s1/2 shell is discussed in relation to the interaction cross‐sections and fragment momentum distributions. Inconsistencies in understanding these data are pointed out. Peculiar changes of shells are discussed for 19C and 23O.