The nature of the phase transitions and proton-deuteron dynamics in the crystals of 9-hydroxyphenalenone derivatives have been investigated by means of solid-state H-2 NMR spectroscopy. It was found that the antiferroelectric ordering of deuterons along the hydrogen bonds in 5-methyl-9-deuterioxyphenalenone (1-d) and 5-bromo-9-deuterioxyphenalenone (2-d) occurs below the phase transition temperatures at T-C = 44 K and T-I = 34 K, respectively. The microscopic origin of the incommensurate modulation in 2-d below T-I = 34 K is attributable to slight rotational displacements, which are fixed at commensurate angles below the lock-in transition at T-C = 22 K.