Results of slow and fast pyrolysis were compared for 1,3,5-trinitrohexahydropyrimidine compounds in which the 5-position was substituted by H, CH3, NO2, CH2ONO2, and CH2N3. IR and Raman spectroscopy were used to identify and quantify all of the gaseous products. The decomposition process appears to be initiated by reactions at the 5-position of the ring. The gases produced are rather similar for all of the compounds, however the different functional groups impart their own signature on the concentrations of several products.