We report our qualitative study of twenty-four students enrolled in the second-semester of a second-year undergraduate (sophomore-level) organic chemistry course, Organic Two. We asked the research participants to propose the product and electron-pushing mechanism of elementary mechanistic steps in the absence and presence of the corresponding overall transformation. We also asked the students about their preferences of representational systems when working on tasks common to Organic Two to ascertain the extent to which an external representation, rather than a task, might evoke a problem-solving strategy. In addition to familiarity to instructional materials, the main reason for which the students preferred line-angle formulas for nearly all of the task types is that the representational system allowed them most readily extract relevant, or otherwise useful, information without distracting them. However, line-angle formulas did not seem to cue students to the three-dimensional attributes of molecules; only dash-and-wedge structures and Newman and chair conformers did so. For the electron-pushing tasks, the research participants’ reasoning processes included at least some chemical characteristics of the species involved in the transformation when they were not given the product of reaction. When provided with the overall transformation, however, the students changed their focus to getting to the product. Consequently, they replaced correct answers with incorrect ones when given the reaction products. These results raise the possibility that traditional mechanism tasks may mask students’ mechanistic reasoning ability.

The only nonsuperconducting rhenium−silicon binary compound, ReSi 1.75 , was heavily p-doped with Ga and Al into ReGaSi and ReAlSi in an attempt to evoke superconductivity. They were synthesized and their crystal structures were studied by both X-ray and neutron diffraction. Si and Ga/Al atoms are ordered into alternating layers, which was rationalized with the "coloring problem" study via first-principles calculations. ReGaSi cannot be further pdoped with more Ga, but ReAlSi can be doped with more Al to ReAl 1.2 Si 0.8 , in which Si and Al atoms are not ordered but randomly distributed on the same sites. The superconductivity measurements over these compounds demonstrate that the ordered ReAlSi and ReGaSi are not bulk superconductors. However, ReAl 1.2 Si 0.8 becomes bulk superconductor with T c = ∼3.5 K, which has been confirmed by magnetism, resistivity, and specific heat measurements.