Studies directed towards the synthesis of metal-containing ketones

The photochemistry of organometallic compounds is receiving increasing attention in the current literature, but as yet, little work has been reported on the photochemistry of metal-containing ketones. The objective of the work reported in this thesis was the synthesis of ligands for the formation of suitable metal-containing ketones. The initial studies were directed at the preparation of β- and ϒ-hydroxyketones by a variety of methods, but the major effort was later concentrated on the synthesis of phosphorus derivatives of o-hydroxyphenyl alkyl ketones . The reaction of o-hydroxyphenyl alkyl ketones with phosphorus trichloride afforded 2-chloro- 1,3,2-dioxaphosphorinans which were readily converted to the corresponding 2-alkoxy derivatives by reaction with various alcohols. Extension of the study to acteylacetone indicated that an analogous reaction occurs to give highly labile products. This part of the work has been accepted for publication in Chemical Communications. The reaction of o-hydroxyphenyl alkyl ketones with other phosphorus halides, such as dichlorophenyl phosphine and chlorodiphenylphosphine, has also been investigated. Reaction of the former reagent with o-hydroxyacetophenone gave a crystalline phosphorus-containing derivative; spectroscopic evidence indicates that this compound possesses an unusual structure and it is currently being studied by X-ray crystallography

Reactivity studies of phosphoric amides and esters

Bibliography: pages 154-161.The effect of protonation and Lewis acid-base interaction on the ¹H n.m.r. chemical shifts of the ester and amide bonds in selected phosphoramidates (RO)₂P(O)NR'₂ was investigated. The results are interpreted in terms of the interaction of the phosphoryl oxygen atom with Lewis acids and oxygen/nitrogen diprotonation in trifluoromethanesulphonic acid. Intramolecular nucleophilic displacement of the halide ion from secondary β-chloroethyl-substituted phosphoramidates X₂P(O)NHCH₂CH₂Cl, diamidates (RO) (MeNH)P(O)NHCH₂CH₂Cl and β-chloroethyl phosphates Y(MeO)P(O)OCH₂CH₂Cl, was studied under conditions of electrophilic (Ag+) and basic (NaH) catalysis. 1,3-Substitution by the nitrogen atom of the phosphdramidates, yielding ethylenimine derivatives was found to be the preferred reaction-pathway; the alternative 1,5-reaction involving the amide nittogen or phosphoryl oxygen atoms was not observed. No intramolecular nucleophilic displacement occurred in the β-chloroethyl phosphate esters

What can student-generated diagrams tell us about their understanding of chemical equations?

Chemical equations are representations that use symbols to summarise the net changes occurring in a reaction whereas depictions such as drawings of the submicroscopic level provide representations of the chemical transformations. While the ability to balance and interpret chemical equations is key to understanding many concepts in chemistry, many undergraduate chemistry students struggle to master these skills. The equations contain a great deal of implicit information and novices may not be able to make the connection between the equation and the actual chemical transformations that are occurring. This paper reports on a study which used submicroscopic diagrams to probe students\u27 understanding of chemical equations. Assessment tasks required students to interpret diagrams, construct diagrams and to relate diagrams to symbolic representations. The analysis showed that some students have misconceptions about the molecular nature and chemical formulae and could not distinguish between coefficients and subscripts when representing chemical formulae. While students were generally able to balance a chemical equation presented as a set of diagrams, a significant number could not generate the balanced equation based on a diagram of the progress of a reaction, The study has demonstrated the use of student-generated diagrams to provide insight into students\u27 understandings of chemical equations.<br /

Student-generated submicro diagrams : a useful tool for teaching and learning chemical equations and stoichiometry

This paper reports on a pedagogical approach to the teaching of chemical equations introduced to first year university students with little previous chemical knowledge. During the instruction period students had to interpret and construct diagrams of reactions at the submicro level, and relate them to chemical equations at the symbolic level with the aim of improving their conceptual understanding of chemical equations and stoichiometry. Students received instruction in symbol conventions, practice through graded tutorial tasks, and feedback on their efforts over the semester. Analysis of the student responses to formative test and summative exam items over consecutive years indicates that there was a consistent improvement in the abilities of the various cohorts to answer stoichiometry questions correctly. The responses provide evidence for diagrams of the submicro level being used as tools for reasoning in solving chemical problems, to recognise misconceptions of chemical formulae and to recognise the value of using various multiple representations of chemical reactions connecting the submicro and symbolic levels of representation. The student-generated submicro diagrams serve as a visualisation tool for teaching and learning abstract concepts in solving stoichiometric problems. We argue that the use of diagrams of the submicro level provides a more complete picture of the reaction, rather than a net summary of a chemical equation, leading to a deeper conceptual understanding.<br /

Increasing the Signal to Noise Ratio in a Chemistry Laboratory - Improving a Practical for Academic Development Students

In practical sessions students lack sufficient time or opportunity for deep processing of information. If the signal to noise ratio is too low, it can obscure the 'chemical message' which the lecturer is trying to convey. This study reports on an action research driven attempt to improve on a Hess's Law experiment, well known in most first year curricula. Data collected in 2000 indicated that students struggled primarily because there were toomanypractical demands to allow them to focus on the concepts involved. The exercise was thus divided into two sessions in 2001, the first to address the issues related to techniques required, the second, similar to the experiment in 2000. Analysis of data collected in 2001 shows that the changes made a significant impact on the effectiveness of the laboratory session. South African Journal of Chemistry Vol.56 2003: 47-5

Teaching of chemical bonding: a study of Swedish and South African students' conceptions of bonding

Almost 700 Swedish and South African students from the upper secondary school and first-term chemistry university level responded to our survey on concepts of chemical bonding. The national secondary school curricula and most common textbooks for both countries were also surveyed and compared for their content on chemical bonding. Notable differences between the countries were found in textbooks and in the curriculum regarding the topics of ionic bonding, bond energetics and use of the VSEPR model, the latter being absent in the Swedish curriculum and ionic bonding not explicitly mentioned in the South African curriculum. To some extent these differences are reflected in the students' responses to the survey. It is also clear that university teachers in both countries must prepare effective counter-measures against deep rooted misunderstandings. For the upper secondary school level it is suggested that the bond energetics and exothermic and endothermic reactions be clearly and carefully presented and separated as the study indicates that mixing of these two concepts is a major cause of confusion

What lies at the heart of good undergraduate teaching? A case study in organic chemistry

This is a post-print of an article published by the Royal Society of Chemistry available at: http://dx.doi.org/10.1039/C1RP90042K.Teaching organic chemistry at the undergraduate level has long been regarded as challenging and students are often alienated by the mass of detail which seems to characterise the subject. In this paper we investigate the practice of an accomplished lecturer by trying to capture and portray his pedagogical content knowledge, PCK, in order to reveal his tacit knowledge as a resource for others. Data analysed from interviews and a set of five introductory lectures showed the framing of Big Ideas designed to underpin later work in the course. Five manifestations of his practice emerged strongly from the data analysis, namely Explanations, Representations, Interaction with Students, Curricular Saliency and Topic Specific Strategies. This realisation allowed us to make inferences about his underlying knowledge and beliefs regarding how the discipline should be taught. We found that the most important aspect of his practice was his recognition of the basic underlying concepts to be mastered before starting the main part of the course, and his strong beliefs related to the learning of the discipline. The extraction and portrayal of these practices are a valuable resource for novice lecturers

Preparedness for tertiary chemistry: multiple applications of the chemistry competence test for diagnostic and prediction purposes

This is a post-print of an article published by the Royal Society of Chemistry available at: http://dx.doi.org/10.1039/C1RP90024B.The development of the Chemistry Competence Test was prompted by the extensive curriculum changes in the South African school system after democracy was established in 1994. As chemists, we were concerned that there might be a lack of articulation between secondary and tertiary levels, since we anticipated that curriculum changes would have an impact on the knowledge base and skills development of prospective students. A diagnostic test developed initially to document proficiencies of first-time entering students to South African universities has proved to be a versatile instrument for multiple uses. Apart from monitoring levels of preparedness for tertiary chemistry during a period of systemic change, it has also been used to evaluate institutional placement policies, to identify specific conceptual problems and procedural deficiencies, and to measure conceptual gains over the course of the first year at university. In addition, its application for the prediction of risk of failure in first-year chemistry based on cognitive and non-cognitive variables was demonstrated. All these findings are valuable resources to inform lecturers who are concerned about minimizing the conceptual gap between secondary and tertiary chemistry

Facilitating adjustment to higher education: towards enhancing academic functioning in an academic development programme

Several studies have emphasised the importance of addressing social and emotional factors in facilitating adjustment to tertiary education. This article describes the Skills for Success in Science programme at the University of Cape Town. The broad aims were life skills development and improved adjustment which are assumed to underpin academic performance. Weekly small group sessions were held which addressed several areas, namely adjustment, group work and co-operative learning, coping and stress management, resources on campus, assertiveness and communications, time management, study skills and examination competence. The intervention was experiential and participative, and while not compulsory, attendance was very good. Evaluation via self-report questionnaires using standardised psychological scales as well as focus groups provided positive feedback from students who described it as a "must" for all first year science students. The article supports the notion that student development should be located within their daily experience at universities

Grade 12 Achievement Rating Scales in the New National Senior Certificate as Indication of Preparedness for Tertiary Chemistry

There has been much discussion on the impact of the new curricula for Grades 10–12 on the preparedness for tertiary studies of the 2009 cohort in subjects such as mathematics, chemistry and physics. Using the Chemical Competence Test that was developed and refined earlier, we have evaluated the proficiencies of incoming students to determine the shifts in preparedness for tertiary chemistry that occurred after students wrote the National Senior Certificate (NSC) in South Africa for the first time in 2008. Data were collected in 2009 for first-time entering students at the Universities of Pretoria (UP) (N = 828) and Cape Town (UCT) (N = 315) and compared with that of students who were educated according to the former National Education curriculum (NATED 550) (2005: NUP+UCT = 776). The raw score results showed a decline in proficiency in all topics, and significantly reduced skills development, with mastery of acids and bases showing the most serious decline. Rasch analysis of the data indicated that a 12 percentage point shift in preparedness occurred in 2009 compared with 2005. The contribution to this shift of a mismatch between the new NSC rating scale and the one used previously was also investigated. The implications of the findings for selection and placement and teaching of first year chemistry courses are discussed