The dielectric properties of pressed discs and/or powders of the following compounds have been investigated in the frequency range 20 Hz to 10 MHz: 1,3-dinitro-1,3-diazacyclopentane; 1,3-dinitro-1,3-diazacyclohexane; 1,3-dinitro-1,3-diazacycloheptane; 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX); 1,3,5-trinitroso-1,3,5-triazacyclohexane; 1,5-methylene-3,7-dinitroso-1,3,5,7-tetraazacyclooctane; 1,3-dithiane; 1,3,5-trithiane; pentafluoronitrobenzene; pentafluoronitrosobenzene; pentafluorotoluene; pentafluoroaniline, pentafluoroanisole; pentafluorophenol and pentafluorobenzonitrile. Evidence for molecular rotation in the solid state is shown by the six and seven-membered ring dinitramines, the cyclic trinitrosamine, 1,3-dithiane, pentafluoronitrosobenzene and pentafluoroaniline. The cyclic nitramines and nitrosamines have atomic polarisations of ca. 9–17 cm3 mol–1. With 1,3-dinitro-1,3-diazacyclohexane and pentachloronitrobenzene the micro-brownian motions in dilute solutions in supercooled o-terphenyl have been investigated.