Uniform thermodynamic description of the orientationally disordered mixed crystals of a group of neopentane derivatives

The experimental systems considered in this paper are isobaric binary plast ic-crystalline mixed crystals of neopentane derivatives, and their properti es studied are (i) solid-liquid phase behavior and (ii) the thermodynamic m ixing properties, actually the excess enthalpy, entropy, and volume. More i n particular, 10 systems are considered, nine being face-centered cubic and one body-centered cubic, and their components are derived from neopentane, C(CH3)(4), by substituting one or more -CH3 groups by one or more -CH2OH g roups and/or one -NO2 or -NH2 groups. The (mean) number of -CH2OH groups pe r molecule appears to have a dominating influence with regard to melting te mperature and degree of compactness. The values of the excess properties va ry from system to system, whereas their quotients are system-independent. F or the group of fee systems, the quotient of excess enthalpy and excess ent ropy (compensation temperature) has the uniform value of 630 K, and the quo tient of excess enthalpy and excess volume the value of about 0.5 GPa.