Science & Mathematics

A computational study has been carried out to examine the feasibility of generating a simple monocyclic cyclopentadienylcation that may be sufficiently stable to isolate and handle at ambient temperatures. Using judicious placement of electron-withdrawing groups (CF3) about the ring we have identified a derivative that may approach the stability of isolobal (and isolatable) borole rings, as evaluated by HOMO–LUMO and singlet–triplet gaps. These Cp+ derivatives may therefore be an attractive target for synthetic isolation.

This paper discusses the creation perspective on economics, ecology and the environment and looks at the problems of species extinction, habitat destruction, land degradation, and pollution of the waters and the atmosphere.

Twenty-seven first-year nursing students, divided across six focus groups formed on the basis of their past chemistry experience, were interviewed about their chemistry experience as a component of a Health Science unit. Information related to learning and academic performance was able to be established from student conversations resulting in three themes (and associated categories): Connectivity (curriculum. application, and social interaction); Reductivity (nature of chemistry. exposition. and control of learning); and Reflexivity (confidence. anxiety, and goal orientation). The framework proved useful in portraying relationships between themes for conversations related to tutorial sessions, prior knowledge, and chemistry in nursing. The focus groups were representative of the total cohort of students in terms of gender, age, working hours, academic performance, enjoyment level of chemistry, and the extent of the relevance of chemistry to nursing. Implications for chemistry educators, especially those supporting novices, are considered.

The kinetic instability of iron(III) thiocyanate complexes in aqueous solution, evidenced by the loss of solution colour with time, has made it difficult to determine reliable equilibrium data. A technique, which measures the absorbance of these solutions as a function of time within milliseconds of mixing Fe³⁺ with SCN^- and which extrapolates to an initial spectrum at time zero, has been designed to overcome these difficulties and is described in this paper. Two complexes, Fe(SCN)²⁺ and Fe(SCN)₂⁺, have been identified upon analysing the absorbance data for thiocyanate concentrations up to 0.25 M at 25^oC and an ionic strength of 0.5 M. Equilibrium constants, K₁ = and K₂ = have been determined and comparisons made with the literature.

The orchid genus Rhizanthella is endemic to Australia and comprises two species, R. gardneri, which is known from a number of sites in S. W. Western Australia and R. slateri, which is now known from six confirmed sites in eastern Australia. One of the most remarkable characteristics of the genus is that almost the entire life cycle is spent underground.

Treatment of the iron(I) synthon L^MeFeNNFeL^Me (L^Me = β-diketiminato ligand) with pivalonitrile gives a formally iron(I) complex L^MeFe(NCtBu)₂, which has one strongly bound side-on nitrile and one weakly bound end-on nitrile ligand. The side-on nitrile ligand has N–C–C bending and N–C weakening that suggests partial reduction of the nitrile group. The S = 3/2 ground state of this molecule can be described as either an iron(II) atom with a nitrile radical anion or an iron(I) atom that is strongly backbonding. DFT computations show that strong backbonding comes from a doubly occupied orbital, and that there is little ligand radical character. Therefore, the iron(I) formulation is the most appropriate. This study exemplifies how one-electron transfer to ligands and two-electron backbonding to ligands may be distinguished by using spectroscopically calibrated and validated computations.[from publisher's website].

The summer benthos of 24 lakes ranging from 1-204 g l-1 salinity contained 27 species of macroinvertebrates. The worm Antipodrilus timmsi, the ostracod Mytilocypris splendida, the amphipod Austrochiltonia subtenuis, the chironomids Procladius spp. and Chironomus duplex aand the snail Coxiella striata were common at lower salinities (3-ca. 30 g l-1) while the crustaceans Australocypris robusta and Haloniscus searlei, the chironomid Tanytarsus barbitarsis and a ceratopogonid larva dominated in salinities ca. 20-100 g l-1. Small ostracods were common from 40-150 g l-1. Diversity changed little with salinity. Mean dry biomass ranged from 0-3.94 g m-2; distribution between lakes was negatively skewed with a peak around 7 g l-1 salinity. Within many lakes, there was considerable spatial heterogeneity which in some cases seemed to result from different bottom characteristics or to point source enrichment. Many groups contributed to the standing crop at low to moderate salinities, and at high salinities crustaceans were important. The lakes were grouped into two low salinity associations, an association which comprised the Red Rock Lakes and a cluster of highly saline lakes. This reflects the grouping of species into halobiont, halophilic and salt-tolerant freshwater species. © 1983 Dr W. Junk Publishers.

This paper reports on students’ understanding of sugar concentration in aqueous solutions presented in two different modes: a visual submicroscopic mode for particles and a verbal mode referring to macroscopic amounts of sugar. One hundred and forty-five tertiary college students studying some form of first-year chemistry participated in the study. For problems of a similar nature, students were much more successful in solving solution concentration problems that were presented verbally than were presented using a submicroscopic representation of particles. The implications of this for chemistry education are outlined in the paper. One contributing factor to the poor success rate with submicroscopic representations (SMR) was possibly the fact that the SMR were presented in multiple-choice format whereas the verbal representations required a short-answer response. While the multiple-choice format may prove deceptive, on account of the way students interpret alternatives containing visual images, students agreed it also proved instructive in highlighting the importance of accounting for volume change in concentration calculations. [from publisher's website].

While Christian communities had no problem engaging positively with the sciences of astronomy, physics and chemistry, they had difficulty engaging with the emerging geology and biology of the 19^th century. The ancient earth and evolutionary models of geology and biology respectively were seen as a direct attack on the biblical Genesis model of a young earth and a creation that took place over the period of a week. Some Christian apologists used Baconianism and the Scottish Common Sense philosophy to suggest that geology was not a real science. Geology was characterised as consisting of wild speculation, hypotheses and theories and lacking in solid factual evidence. In both Britain and North America Christian respondents to the new geology were classified as harmonizing geologists or scriptural geologists. This paper considers the nature of these respondents, their philosophical positions, and how these positions took form in the succeeding centuries in terms of different cognitive geological styles. The implications for the science education and science in society context will be discussed.

In this paper we report on the use of [NO][BF4] to access tricationic tetrakis(pyridine)gold(III) from Au powder, a species inaccessible using the more traditional (tetrahydrothiophene)AuCl route. It is then demonstrated that this family of compounds can be used to access new terminal Au(III) hydroxides, a challenging class of compounds, and the first crystallographically characterized examples employing bidentate ligands. Finally, preliminary biological studies indicate good activity for derivatives featuring polydentate ligands against the HeLa and PC3 cell lines but also strong inhibition of primary HUVEC cells.

Density functional calculations have been employed to rationalize why the heteronuclear N₂-bridged Mo^IIINb^III dimer, [Ar(^tBu)N]₃Mo(µ-N₂)Nb[N(ⁱPr)Ar]₃ (Ar = 3,5-C₆H₃Me₂), does not undergo cleavage of the dinitrogen bridge in contrast to the analogous Mo^IIIMo^III complex which, although having a less activated N–N bond, undergoes spontaneous dinitrogen cleavage at room temperature. The calculations reveal that although the overall reaction is exothermic for both systems, the actual cleavage step is endothermic by 144 kJ mol⁻¹ for the Mo^IIINb^III complex whereas the Mo^IIIMo^III system is exothermic by 94 kJ mol⁻¹. The reluctance of the Mo^IIINb^III system to undergo N₂ cleavage is attributed to its d³d² metal configuration which is one electron short of the d³d³ configuration necessary to reductively cleave the dinitrogen bridge. This is confirmed by additional calculations on the related d³d³ Mo^IIINb^II and Nb^IINb^II systems for which the cleavage step is calculated to be substantially exothermic, accounting for why in the presence of the reductant KC₈, the [Ar(^tBu)N]₃Mo- (µ-N₂)Nb[N(ⁱPr)Ar]₃ complex was observed to undergo spontaneous cleavage of the dinitrogen bridge. On the basis of these results, it can be concluded that the level of activation of the N–N bond does not necessarily correlate with the ease of cleavage of the dinitrogen bridge.

The activation and scission of the N–O bond in nitric oxide using dinuclear mixed-metal species, comprising transition elements with d³ and d² configurations and trisamide ligand systems, have been investigated by means of density functional calculations. The [Cr(III)–V(III)] system is analyzed in detail and, for comparative purposes, the [Mo(III)–Nb(III)], [W(III)–Ta(III)], and (mixed-row) [Mo(III)–V(III)] systems are also considered. The overall reaction and individual intermediate steps are favourable for all systems, including the case where first row (Cr and V) metals are exclusively involved, a result that has not been observed for the related dinitrogen and carbon monoxide systems. In contrast to the cleavage of dinitrogen by three-coordinate Mo amide complexes where the dinuclear intermediate possesses a linear [Mo–NN–Mo] core, the [M–NO–M′] core must undergo significant bending in order to stabilize the dinuclear species sufficiently for the reaction to proceed beyond the formation of the nitrosyl encounter complex. A comparative bonding analysis of nitric oxide, dinitrogen and carbon monoxide activation is also presented. The overall results indicate that the π interactions are the dominant factor in the bonding across the [M–L¹L²–M′] (L¹L² = N–O, N–N, C–O) moiety and, consequently, the activation of the L¹–L² bond. These trends arise from the fact that the energy gaps between the π orbitals on the metal and small molecule fragments are much more favourable than for the corresponding σ orbitals. The π energy gaps decrease in the order [NO < N₂ < CO] and consequently, for each individual π orbital interaction, the back donation between the metal and small molecule increases in the order [CO < N₂ < NO]. These results are in accord with previous findings suggesting that optimization of the π interactions plays a central role in increasing the ability of these transition metal systems to activate and cleave small molecule bonds.

N-heterocyclic carbenes (NHCs) are generally considered to be extremely robust, ideal spectator ligands. However, in the past two years there have been several reports of the activation of the endocyclic C–N bond with subsequent insertion into element–hydrogen and element–carbon bonds. The new reaction pathway casts the reactivity of the NHC heterocyclic ring into a new light, especially in the context of potential catalyst decomposition. The synthetic reports and theoretical studies in this rapidly developing area are summarized here.

There are inherent difficulties in a subject like chemistry particularly the notion of a chemical reaction. In this paper the difficulties are discussed from a teaching and learning perspective and from a history of chemistry perspective. Three teaching/learning studies of the incompleteness of the iron(III) thiocyanate reaction in chemical equilibrium are reviewed and it is shown that a recent historical study of the iron(III) thiocyanate reaction has the potential to challenge the interpretation of the incompleteness of the reaction. This establishes a controversial context where students can be introduced to epistemic thinking, that is, how to interrogate chemistry data and form a conclusion which resonates with what we know about the nature of science. A curriculum suggestion for pre-service chemistry teachers is provided.

Fifteen first-year nursing students individually took part in structured interviews in which a range of devices related to nursing practice and fluid physics was considered. Analysis of the transcripts of these interviews revealed that although respondents had already completed the section of their course related to fluid physics, the majority still exhibited inconsistent and naive ideas about the fluid state, pressure and fluid flow. After structured intervention however, some responses in the latter portion of the interviews gave evidence of conceptual development and an increasing ability to generalise physical principles in contexts not previously encountered.

Part of the apparent variation in community structure and abundance of macrobenthos between lakes is attributable to the different sampling strategies used. A comparison of 7 sampling options in Lake Pearson, Canterbury, New Zealand, shows that spot samples and line transects are inadequate but that an augmented line transect is almost as good as stratified random sampling. Winter/early spring and summer samples are needed to account for seasonal variations in species richness and community biomass. Much less effort is required for an augmented line transect, therefore it is recommended for lake survey and management studies.

750 reptile specimens comprising 38 species, representing 30 genera and 7 families were examined from the Wagga Wagga area. A further 9 species might be expected to occur in the area or nearby regions. Two species not previously recorded from the area, Gehyra variegata and Lerista muelleri are south-east range extensions for these species. Significant habitat alteration in the area has probably resulted in reduction in reptile numbers and the species densities. Fractionation of habitat has resulted in the isolation of many populations.

This article uses the strategy of a historical essay with the periodic table as its theme to engender in tertiary-level students a sense of the progress of chemistry as a human endeavour. This has great value in helping students address issues related to the nature of science. The author's objective is to overcome the expressed view that technical jargon not rooted in experience and factual overload makes it difficult to gain a sense of how concepts and theories originate, how they come to be validated and accepted, and how they connect with experience and reveal relations among seemingly disparate phenomena. A key feature of the nature of science particularly applicable to the Periodic Law is outlined and discussed with reference to the work of Dobereiner, Newlands, Mendeleeff, and recent observations by Scerri. The paper includes discussion of the fallibility of any basis for periodic organisation of the elements, and the idea that a better organising principle might be a non-visualisable property of atoms such as total energy. A teaching/learning strategy used by the author with a first year tertiary chemistry class is outlined. [Author abstract, ed]

In the late 19th and early 20th centuries Svante Arrhenius and Henry Armstrong understood the dissolution process of salts in water quite differently. Arrhenius saw the dissolution process as one whereby the salt partially dissociated into its ions and Armstrong saw the dissolution process as one whereby the salt associated itself with water. History is somewhat kinder to Arrhenius than it is to Armstrong in that Arrhenius won the Nobel Prize for Chemistry in 1903 for his electrolytic dissociation theory whereas Armstrong was considered of a 'hot air balloon' who made it his business to oppose every new thought in chemistry. In the 1920s Arrhenius' view of partial dissociation was replaced by a view of total dissociation for strong electrolytes with activity and osmotic coefficients being used to account for non-ideal solution behaviour. However, recent research has shown that strong 1:1 electrolytes are best understood by using Arrhenius' original idea of partial dissociation rather than total dissociation and Armstrong's idea of hydration. This strange confluence of factors has important implications for chemical epistemology and its role in chemistry education.