The experimental binary phase diagram between the pure components 2-methyl-2-nitro-1-propanol (MNP) and 2-hydroxymethyl-2-methyl-1,3-propanediol (PG) has been established from 273 K to the liquid state, using thermal analysis and X-ray powder diffraction at several temperatures. The main features of this phase diagram, such as, the miscibility and the molecular interactions in plastic phase are discussed on the basis of the similarity in shape and size of the molecules. In addition, other binary systems, previously reported by us, between neopentane-like compounds which present a comparable situation are considered.