Conformational trimorphism of bis(2,6-dimesitylphenyl)ditelluride

Besides the previously known α-form (monoclinic, P21/c, Z=4) of bis(2,6-dimesitylphenyl)ditelluride, two new polymorphic modifications, namely the β-form (monoclinic, P21/c, Z=8) and the γ-form (triclinic, P1̅, Z=2), were obtained serendipitously during chemical reactions. In all three modifications, the individual molecules possess significantly different conformations and bond parameters, such as Te–Te bond lengths, C–Te–Te bond angles, C–Te–Te–C torsion angles and intramolecular Menshutkin interactions, which is also reflected in their non-covalent interactions with adjacent molecules in the crystal lattice via London dispersion and electrostatic forces. The interplay between intermolecular and intramolecular forces in these conformational polymorphs was investigated using quantum chemical calculations, which reveal that the β-form should be thermodynamically stable at absolute zero. In contrast, crystallization experiments and thermoanalytical investigations indicate that the α-form is stable at high temperatures and therefore, both forms might be related by enantiotropism.

High Pressure Raman Study of Layered Semiconductor Tlgase2

Raman spectroscopy measurements of a monoclinic layered semiconductor TlGaSe2were performed in a pressure range up to 10.24 GPa. The pressure-induced first-order phase transition accompanied by reconstruction of the layer structure was observed at the pressure P ~ 0.9 GPa. The mode-Grüneisen parameters of intralayer bonds were calculated for TlGaSe2. The contribution of thermal expansion to temperature changes of phonon frequencies was defined. The type of intralayer bonds and their pressure transformation were analyzed in layered TlGaSe2. It was shown that the nature of intramolecular forces in molecular crystals and intralayer forces in layered GaS, GaSe and TlGaSe2is similar

Gas-phase structure of 1,8-bis[(trimethylsilyl)ethynyl]anthracene: cog-wheel-type vs. independent internal rotation and influence of dispersion interactions

1,8-Bis[(trimethylsilyl)ethynyl]anthracene is extremely flexible and difficult to predict by DFT methods; gas electron diffraction plus molecular dynamics calculations enlighten competing intramolecular forces.

Are creative comparisons developed by prospective chemistry teachers evidence of their conceptual understanding? The case of inter- and intramolecular forces

The aim of this study is to determine prospective chemistry teachers' creative comparisons about the basic concepts of inter- and intramolecular forces, and to uncover the relationship between these creative comparisons and prospective teachers' conceptual understanding. Based on a phenomenological research method, this study was conducted with 101 prospective chemistry teachers studying in the Chemistry Education Department at a state university in Turkey in the academic year 2011–2012. The research made use of two data collection instruments, a creative comparison questionnaire and semi-structured interviews. The concepts of “non-polar covalent bonds, dipole–dipole force, hydrogen bonds, ionic bonds, covalent bonds, polar covalent bonds, and van der Waals force” were set out in the creative comparison questionnaire and the prospective teachers were asked to complete the sentences about these concepts (example: ionic bond is like .......... because ...........). Content analysis techniques were employed in the analysis of the creative comparisons set out in the questionnaire. The analysis of the data revealed that the prospective teachers generally developed their creative comparisons based on the formation and strength of the different bonds and that they also had alternative conceptions, particularly regarding the formation of covalent bonds, hydrogen bonds, and the van der Waals force. Semi-structured interviews were conducted in order to learn more about this and obtain detailed information about the level of understanding of the prospective teachers. Twelve prospective teachers were selected for the interviews on the basis of the creative comparisons they had developed in the creative comparison questionnaire. The analysis of the interviews showed that the level of conceptual understanding of the prospective teachers was not tightly linked to the complexity of their creative comparisons. However, it was seen that the creative comparisons submitted by the prospective teachers could be used to infer their conceptual understanding. Also, these creative comparisons could be helpful in determining what the prospective teachers' alternative conceptions were.