RDX is made by the nitration of hexamethylene tetramine, better known by its trivial name of hexamine.

    CH2 ----- N
   /         / \
  /        CH2  \
 /         /     \
N - CH2 - N       CH2
 \        \      /
  \       CH2   /
   \        \  /
    CH2 ----- N

      Hexamine

            NO2
            /
      CH2--N
     /      \
O2N-N        CH2
     \      /
      CH2--N
            \
             NO2

       RDX