Isomorphism of 2-methylnaphthalene and 2-halonaphthalenes as a revealer of a special interaction between methyl and halogen

Abstract

The systems 2-methylnaphthalene+2-chloronaphthalene and 2-methylnaphthalene+2-bromonaphthalene belong to the exceptional group of binary systems where the formation of mixed crystals goes together with a solid–liquid phase diagram with a maximum. For these systems a thermodynamic analysis is presented which is based on new phase diagram and thermochemical data. The excess Gibbs energies, excess enthalpies, and excess entropies of the mixed crystalline state all are negative. These properties correspond to a net attraction between methyl and substituted halogen. Additional evidence of such an attraction is given by the outcome of a statistical search on intermolecular contacts, in the crystalline state of pure substances, among methyl+halogen, halogen+halogen, and methyl+methyl.

Connecting the normal pressure equilibria of the two-component system CCl(CH3)3+CBrCl3 to the pressure–temperature phase diagrams of pure components

“…Of special relevance in this two-component system is the maximum and minimum for the [R + FCC] two-phase equilibrium, because there are very few systems showing a solid-solid equilibrium with such extremes [26,27]. Similar behaviour has been recently found for the system CCl 4 + CBr(CH 3 ) 3 system [28].…”

From High-Temperature Orientationally Disordered Mixed Crystals to Low-Temperature Complex Formation in the Two-Component System (CH3)3CBr + Cl3CBr

“…On these grounds, a relevant parameter to account for is the intermolecular distances be tween halogen and methyl entities of first neighbor molecules. 44 As nicely established in the work of Calvet et al 44 for a large number of molecular compounds in which the halogen and methyl group are involved, the comparison between the fre quency distributions of the shortest intermolecular contacts between CH 3 3 3 3 CH 3 , Br 3 3 3 Br, and CH 3 3 3 3 Br reveals that the last distribution has a more pronounced peak than those of CH 3 3 3 3 CH 3 and Br 3 3 3 Br. The authors conclude that the CH 3 3 3 3 X (halogen) interaction is stronger than the average of the CH 3 3 3 3 CH 3 and X 3 3 3 X interactions.…”

“…The experimental evidence means that the intermolecular interactions CH 3 3 3 3 X(halogen) are stronger within the com plexes than within the pure compound, giving strong support to the arguments and facts provided by the work of Calvet et al concerning the methyl-halogen particular interaction. 44…”

“…The second relevant aspect concerns experimental evidence related to two-component phase diagrams sharing molecules in which methyl and halogen entities are involved. Some years ago Calvet et al reported on several binary phase diagrams composed of chemically homologous molecules, in particular, 2- methyl naphthalene + 2- chloro naphthalene and 2- methyl naphthalene + 2- bromo naphthalene, as exceptional cases in which the formation of mixed crystals goes together with the existence of a solid−liquid two-phase equilibrium with a maximum. The authors argued through a careful thermodynamic assessment of phase diagrams that the consequence of such exceptionality is the net attraction between methyl and halogen (Cl or Br) which gives rise to negative values of the excess thermodynamic properties of the mixed crystals.…”

Isomorphism and mixed crystals in 2-R-naphthalenes: evidence of structural subfamilies and prediction of metastable forms

“…These ten systems have been studied by X-ray diffraction and by thermal analysis. A thermodynamic analysis of the solid±liquid equilibria in three binary systems shared by 2-methylnaphthalene, 2-chloronaphthalene and 2-bromonaphthalene, and a statistical search on intermolecular distances in pure substances, permit us to conclude the evidence of a net attraction between methyl and halogen (Calvet et al, 1999). In this section the experimental results, in the form of graphical representations, are given for the four systems that have 2-¯uoronaphthalene as one of the components.…”