Pressure-Temperature equilibrium curves crystalline/plastic, crystalline/vapour and plastic/vapour have been determined in Neopentylglycol and 2-Methyl-2-nitro-1-propanol, plastic crystals derived from Neopentane. The pressure measurements have been carried out employing a thermobarometric system (crystalline/plastic) and the Knudsen effusion method (vapour pressure). Equations of the type lnP=-B/T+A have been used to fit experimental vapour pressure values.