Now showing 1 - 3 of 3
  • Publication
    Open Access
    Formation of “A-frame” dirhenium(I) hexacarbonyl complexes by trans-1,2-bis(diphenylphosphino)ethylene and bis(bidentate) ligands
    (2015)
    Kee, Chee Leong
    ;
    Zhou, Feng
    ;
    Su, Haibin
    ;
    A series of A-frame dirhenium(I) hexacarbonyl complexes bridged by trans-1,2-bis(diphenylphosphino)-ethylene (dppene) and bis(bidentate) ligands (L) were synthesized: [Re2(μ-dppene)(CO)6(μ,η2:η2-L)] (L = 1,2-dithioooxalate, 1; tetrathiooxalate, 2; dithiooxamidate, 3 and oxamidate, 4). X-ray crystallographic analysis of 1–3 confirmed that the dppene ligand adopts a syn bridging conformation with nearly eclipsed P–Re bonds in these complexes. The angle between the phosphorus lone pairs of the diphosphine is adjusted to suit different Re⋯Re distances (5.6–6.4 Å) mainly by twisting the ethylene Cdouble bond; length as m-dashC bond and enlarging the P–Cdouble bond; length as m-dashC angles of the phosphine backbone. Complex 2 forms dimers in the solid state via intermolecular S⋯S interactions (3.39 Å). Proton and 31P NMR data indicate that these dimers persist in chloroform solution but not in DMSO. Natural bond orbital analysis revealed the S⋯S interactions to be between the orbital occupied by the lone pair electrons in each sulphur atom as a donor, and virtual orbitals consisting of S–C σ*, S–Re σ*, and S–C π* states on the acceptor sulphur atom. The binding energy of the dimer was explicitly computed to be 8.14 kcal/mol.
    WOS© Citations 8Scopus© Citations 7  178  130
  • Publication
    Open Access
    Diagnostic appraisal of grade 12 students’ understanding of reaction kinetics
    (2016) ;
    Subramaniam, R. (Ramanathan)
    The study explored grade 12 students’ understanding of reaction kinetics, a topic which has not been extensively explored in the chemistry education literature at this level. A 3-tier diagnostic instrument with 11 questions was developed – this format is of very recent origin and has been the subject of only a handful of studies. The findings reveal that reaction kinetics is not an easy topic for the students to understand. A total of 23 alternative conceptions (ACs) as well as some indication of their strengths and other confidence-related measures have been documented for the students (N=137) – most of these ACs have not been reported before. When the overall scores of the students in the diagnostic test are ranked, it was found that there are a number of differences in the ACs held by students in the top and bottom 25 % of the sample. While most of the ACs held by these groups are common to the overall sample, a number of these are not found in the overall sample. The findings further underscore the diagnostic utility of the 3-tier format. Some implications of the findings are discussed.
    WOS© Citations 10  220  548
  • Publication
    Open Access
    An investigation of Singapore preschool children’s emerging concepts of floating and sinking
    (2017) ; ;
    Ong, Monica Woei Ling
    Despite Singapore’s excellent science achievements in international benchmark tests such as the Trends in International Mathematics and Science Study (TIMSS) and Programme for International Student Assessment (PISA), little is known about Singaporean children’s (aged 4-8) emerging science conceptions as formal science schooling begins at Grade 3 (aged 9). This paper builds on the well-established literature on preschool children’s emerging conceptions and play to illuminate children’s ideas about floating and sinking. Using narratives of a 90-minute activity involving a group of Singaporean children aged 6, we surfaced emerging conceptions that an object floats or sinks due to its weight, and that objects sink because water is “soft”—a conception that has not been reported in previous literature.We also observed a shift from binary discourse about floating and sinking to more graded descriptions (e.g. “sink a bit”) as the children played more. The play-based activity provided opportunities for the children’s emerging conceptions to be elicited because it was conceptually-oriented and created opportunities for social interactions. It allowed children who were not proficient in standard English to express their thinking in actions. In sum, this paper illustrates how play-based contexts could be used to identify children’s emerging conceptions. Early childhood educators in Singapore could pay greater attention to what children say and do during play as these offer rich grounds for identifying and developing children’s emerging conceptions.
    WOS© Citations 2Scopus© Citations 8  368  170