  The dissociation features in nuclear track emulsion of $^9$Be, $^{9,10}$C,
and $^{12}$N nuclei of 1.2 A GeV energy are presented. The data presented for
the nucleus $^9$Be can be considered as evidence that there is a core in its
structure in the form of 0$^+$ and 2$^+$ states of the $^8$Be nucleus having
roughly equal weights. Events of coherent dissociation $^9$C$\rightarrow 3^3$He
associated with the rearrangement of the nucleons outside the
$\alpha$-clustering are identified. A pattern of the charge fragment topology
in the dissociation of $^{10}$C and $^{12}$N nuclei is obtained for the first
time. Contribution of the unbound nucleus decays to the cascade process
$^{10}$C$\rightarrow ^9$B$\rightarrow ^8$Be is identified.
