Molecular alloys in the series of para-disubstituted benzene derivatives. Part VII. The para-dibromobenzene + para-bromoiodobenzene and para-chloroiodobenzene + para-bromoiodobenzene systems

The solid-liquid phase diagrams of the systems para-dibromobenzene + parabromoiodobenzene and para-chloroiodobenzene + para-bromoiodobenzene are presented. In the case of the first system there is solid state miscibility in all proportions and the phase diagram has a minimum. The second system has a solid-liquid loop without extremum and at lower temperature a region of demixing. The crystalline parameters of the molecular alloys have been determined as a function of composition

Mise au point sur le comportement énergétique et cristallographique des n-alcanes

Une mise au point sur le polymorphisme des n-alcanes, n allant de 8 à 21, est proposée au travers d'une étude énergétique (caractérisation des températures et des enthalpies de transitions) et cristallographique (paramètres de maille). Ces composés se classent en deux sous-familles selon la parité du nombre de carbones dans la chaîne. Les alcanes à n impair présentent un polymorphisme: ils passent d'une forme orthorhombique O (Pbcm, Z = 4) à basse température à une forme orthorhombique désordonnée rotatoire Ri (Fmmm, Z = 4) avant de fondre; pour le C9H20 et le CllH24, une phase supplémentaire triclinique T* (PĪ,Z = 2) précède la forme O. La sous-famille à nombre pair est caractérisée par l'existence d’une seule phase stable triclinique (T, PĪ, Z = 1) avant fusion. Nous montrons que cependant, une phase métastable de type rotatoire Ri peut être observée pour le C20. (Reçu le 2 février 1996 ; accepté le 29 mars 1996

Molecular mixed crystals from a macroscopic thermodynamic point of view

It is shown that Kitaigorodsky's qualitative notion of the relation between geometrical similarity and the formation of molecular mixed crystals can be put on a quantitative basis. The quantifiable property is the excess Gibbs energy difference between liquid and solid mixtures. The latter can be derived from binary solid-liquid phase-diagrams by means of thermodynamic phase-diagram analysis. This was shown by applying phase-diagram analysis to the fifteen phase diagrams shared by naphthalene and the five of its 2-R derivatives with R = F, Cl, Br, SH, CH3

Coefficients of molecular homeomorphism and crystalline isomorphism in the series of para-disubstituted benzene derivatives

For binary systems between para-disubstiluted benzene derivatives with Cl, Br, I, the coefficient εk of molecular homeomorphism as well as the coefficient εm of crystalline isomorphism arc given. These coefficients, calculated from crystallographic data, allow a comparison of the crystal buildings

The γ-form of n-eicosanol

In the crystal of the title compound, C20H42O, the mol­ecules are packed in layers parallel to the (100) plane. The alkyl chains are parallel to the [30inline image] direction and these molecular chains are hydrogen‐bonded into chains parallel to the c axis. All C¿C bonds of the alkyl chain show an antiperiplanar (trans) conformation, with a slight deviation from the ideal value (180°) in the C¿C bonds close to the hydrogen bonds. The length of the alkyl chain is 27.92 (2) Å and the tilt angle is 59.7 (2)°

From concept to application. A new phase change material for thermal protection at-11 degrees C

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