2-Acetyl-4,6,8,10,12-pentanitro-2,4,6,8,10,12-hexaazaisowurtzitane (PNAIW) is formed in the last step of nitration of acetyl isowurtzitane derivatives. The amount of the PNAIW formed depends on the conditions of the nitration reaction (temperature, time, and nitrating mixture used) and on the type of the starting acetyl intermediate. The highest PNAIW yields (30%) were obtained by nitrating 2,6,8,12-tetraacetylhexaazaisowurtzitane (TAIW) at 60 degrees C for half an hour using HNO(3)/H(2)SO(4) nitrating mixture. HPLC, NMR, FTIR, and DSC measurements were used in the study and their results are reported.