Conjecture existed as to the molecular structure of the crystalline organic peroxide reaction product derived from the acidified aqueous mixture of urea, formaldehyde, and hydrogen peroxide. This study used X-ray crystal structure determination to unequivocally define the reaction product as the 14-membered ring structure tetramethylene diperoxide dicarbamide (TMDD). Crystals of TMDD belong to the monoclinic space group Pc, a = 4.587(4), b = 16.080(2), c = 6.690(5) angstrom, beta = 107.44(5)degrees. The crystal contains one crystallographically independent molecule with approximate C-s symmetry. Intramolecular p-stacking of the carbonyl groups is a feature, while intermolecular H-bonding between the N-H and C=O functionalities affords linear polymeric strands that is associated with the extremely fine needle crystal morphology that necessitated synchrotron radiation for the structure determination. Sensitiveness testing examining susceptibility to initiate due to heat, impact, friction, and electrostatic stimuli was conducted to gauge the hazards associated with the material. It was revealed to be a primary explosive, particularly susceptible to impact initiation.