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A new ent-kaurane diterpenoid, lophanthodin G (1) and one known abietanoid, 6alpha-hydroxyferruginol (2), were isolated from the leaves of Isodon lophanthoides var. geradianus. The structure of the new compound 1 was established using spectroscopic methods including extensive 1D and 2D NMR analysis.

Previous studies have indicated that A‐level students in the UK and Singapore have difficulty learning the topic of ionisation energy. A two‐tier multiple‐choice instrument developed in Singapore in an earlier study, the Ionisation Energy Diagnostic Instrument, was administered to A‐level students in the UK, advanced placement high school students in the USA, and first‐year university students in China, New Zealand, and Spain to determine whether the students from different countries and educational systems had similar conceptions and difficulties as the students in Singapore with the concepts assessed in the instrument. The results showed that, in general, the students in all six samples had similar alternative conceptions, which were grouped under the categories of octet rule framework, stable fully‐filled and half‐filled subshell conceptions, and conservation of force thinking. The students also resorted to relation‐based thinking when answering items involving the trend of ionisation energies across P...

The topic of ionisation energy is important as the concepts involved provide the foundation for the understanding of atomic structure, periodic trends and energetics of reactions. Previous research has shown that A-level (high school) students in the United Kingdom had difficulty understanding the concepts involved in ionisation energy. This paper describes the development and administration of a two-tier, multiple-choice instrument on ionisation energy, the Ionisation Energy Diagnostic Instrument, to determine if A-level students (Grade 11 and 12, 17 to 18 years old) in Singapore have similar alternative conceptions to those of their counterparts in the United Kingdom, as well as explore their understanding of the trend of ionisation energies across Period 3. The items in such instruments are specifically designed to identify alternative conceptions and misunderstandings in a limited and clearly defined content area. The results showed that students in Singapore applied the same octet rule framework and conservation of force thinking to explain the factors influencing ionisation energy as the students in the United Kingdom. In addition to the above alternative frameworks, many students in Singapore also resorted to relation-based reasoning to explain the trend of ionisation energies across Period 3 elements. [Chem. Educ. Res. Pract., 2005, 6 (4), 180-197]

This article is an overview of traditional chinese medicine. It discusses the general situation of TCM in China and the value of China TCM export market.

Anthocyanins are naturally occurring compounds that impart color to fruits, vegetables, and plants. They are probably the most important group of visible plant pigments besides chlorophyll. Apart from imparting color to plants, anthocyanins also have an array of health-promoting benefits, as they can protect against a variety of oxidants through a various number of mechanisms. However, anthocyanins have received less attention than other flavonoids, despite this. This article reviews their biological functions and pre-clinical studies, as well as the most recent analytical techniques concerning anthocyanin isolation and identification.

The experimental results showed that ozone (O3) oxidation is an effective means to destroy phenolic organic pollutants present in water. High removal efficiencies can be readily achieved for most of the model compounds fortified in aqueous matrices within a reasonable time frame. This study also included the oxidation of phenolic compounds using ozone in combination with ultraviolet (UV) irradiation. The extent of mineralization measured in terms of the losses in total organic carbon is promoted by the joint action of ozone and UV in comparison with using ozone alone.

Ten flavonoid compounds were isolated from the dried leaves of Polygonum hydropiper L. (Laksa leaves), and identified as 3-O-alpha-L-rhamnopyranosyloxy-3',4',5,7-tetrahydroxyflavone; 3-O-beta-D-glucopyranosyloxy-4',5,7-trihydroxyflavone; 6-hydroxyapigenin; 6"-O-(3,4,5-trihydroxybenzoyl) 3-O-beta-D-glucopyranosyloxy-3', 4', 5, 7-tetrahydroxyflavone; scutillarein; 6-hydroxyluteolin; 3',4',5,6,7-pentahydroxyflavone; 6-hydroxyluteolin-7-O-beta-D-glucopyranoside; quercetin 3-O-beta-D-glucuronide; 2"-O-(3,4,5-trihydroxybenzoyl) quercitrin; quercetin. Evaluation of the antioxidative activity, conducted in vitro, by using electron spin resonance (ESR) and ultraviolet visible (UV-vis) spectrophotometric assays, showed that these isolated flavonoids possess strong antioxidative capabilities. Measurement of the Trolox equivalent antioxidant capacity (TEAC) values, against ABTS (2,2'-azinobis(3-ethyl-benzo-thiazoline-6-sulphonic acid) radicals and phenyl-tert-butyl nitrone (PBN) azo initiator (AI) also showed strong anti-oxidative activity. The most powerful of the antioxidants was 2"-O-(3,4,5-trihydroxybenzoyl) quercitrin (galloyl quercitrin). A combination of two flavonoid compounds was tested for synergistic anti-oxidative capacity, but no significant improvement was observed.

This article describes the development and application of a two-tier multiple choice diagnostic instrument to assess high school students' understanding of inorganic chemistry qualitative analysis. The development of the diagnostic instrument was guided by the framework outlined by Treagust. The instrument was administered to 915 Grade 10 students (15 to 17 years old) from 11 schools after they had learned the theory involved in qualitative analysis and after a series of qualitative analysis practical sessions. The Cronbach alpha reliability of the instrument was .68, the facility indices ranged from .17 to .48, and the discrimination indices ranged from .20 to .53. The study showed that the Grade 10 students had difficulty understanding the reactions involved in the identification of cations and anions, for example, double decomposition reactions, the formation and reaction of complex salts, and thermal decomposition. The findings of the study and literature on practical work were used to develop a qualitative analysis teaching package. © 2002 Wiley Periodicals Inc. J Res Sci Teach 39: 283–301, 2002

Grade 10 students in Singapore find qualitative analysis one of the more difficult topics in their external examinations. Fifty-one grade 10 students (15-17 years old) from three schools were interviewed to investigate their perceptions about learning qualitative analysis and the aspects of qualitative analysis they found difficult. The results showed that students found qualitative analysis tedious, difficult to understand and found the practical sessions unrelated to what they learned in class. They also believed that learning qualitative analysis required a great amount of memory work. It is proposed that their difficulties may arise from not knowing explicitly what is required in qualitative analysis, the content of qualitative analysis, the lack of motivation to understand qualitative analysis, cognitive overloading, and the lack of mastery of the required process skills.

This work is an extension of the two previous studies which aims at verifying the importance of the cognitive variables to problem solving in Chemistry across topics and levels. The previous studies show that the five cognitive variables namely, Specific Knowledge, Non-Specific but Relevant Knowledge, Concept Relatedness, Idea Association and Problem Translating Skill, are the important predictors of problem-solving performance in the topic of Grade 12 Electrochemistry. This present study involved 115 Grade 9 Chemistry students, aged between 13 and 16, solving Mole Concept problems with the familiarity levels ranging from familiar to partially familiar. Four of the five cognitive variables, Specific Knowledge, Concept Relatedness, Idea Association and Problem Translating Skill, have been found to be significant in predicting problem-solving performance with Idea Association being the most significant. The study also suggests that the difference in the topics and levels appeared to have little effect on the importance of these variables on problem-solving performance. [Chem. Educ. Res. Pract. Eur.: 2001, 2, 285-301]

The purpose of this study was to investigate the extent to which science teachers taught problem solving in elementary science. The survey involved 348 teachers in 36 Singapore elementary schools. The study investigated the science teachers’ views about their use of science instructional techniques in general and the problem-solving teaching approach in particular. It also focused on the difficulties faced by science teachers in implementing the problem-solving teaching approach in the science classroom. It was found that the most emphasised activities were completion of science workbooks, teachers’ explanation of concepts, and hands-on activities. The least emphasised activities were computer-based learning, activities beyond the textbook and workbook, and visits to the ecology garden and other parts of the school. Only about one-third of the teachers often conducted activities pertaining to problem solving. Most of them were more concerned about covering the science syllabus for examinations, the physic...

An amperometric mediated glucose biosensor has been developed based on a sol–gel derived carbon composite material. Glucose oxidase and the mediator vinylferrocene have been immobilised within the porous, rigid and organically modified silicate network in the composite material. The organic group in the silicate network controls the hydrophobicity of the electrode surface and thus limits the wettability of the electrode surface. Various important fabrication factors controlling the biosensor performance have been investigated systematically. The glucose biosensor can be renewed easily in a reproducible manner by a simple polishing step and it has a long operational lifetime. Applicability of the biosensor has been demonstrated in real samples and the results obtained by this biosensor corroborate well with a classical UV spectrophotometric technique.

Two aromatic ammonium/sodium hydrogen phosphomolybdates (VI), (C15N3H16.75)Na0.25[HMo5P2O1.55]·3H2O (1) and (C30N6H32.5)Na0.5[H3Mo6P4O33]·7H2O (2), were synthesized from hydrothermal reaction of MoO3·H2O, Na3PO1, 1,5-diamino-naphthalene and H2O at 120°C and pH = 2.5−3.5. Compound 1 consists of layers of mixed covalent-hydrogen-bonded sodium hydrogen phosphomolybdenum polyanions which are separated by protonated naphthalene-1,5-diammonium cations and water molecules. Compound 2 consists of chains of mixed covalent-hydrogen-bonded sodium hydrogen phosphomolybdenum polyanions, protonated naphthalene-1,5-diammonium cations and water molecules. The crystal structures of the two compounds were determined using the single crystal X-ray diffraction method. The monoprotonated anion of 1 and triprotonated anion of 2 consist of edge-sharing MoO6 octahedra, corner-sharing PO4 tetrahedra and NaO6 octahedra. The interactions between the anions, which are established through hydrogen bonds involving terminal POH groups, lead to the formation of mixed covalent-hydrogen-bonded layers in 1 and chains in 2 along the [010] direction. The naphthalene-1,5-diammonium cations in both compounds adopt two orientations, however, some of these cations in 1 are disordered. The π-π interactions are observed between naphthalene-1,5-diammonium cations in both compounds 1 and 2.

An amperometric enzyme electrode for phenolic compounds was developed via an easy and effective immobilization method using the sol–gel technique. The enzyme electrode comprises tyrosinase immobilized by the thin silica sol–gel layer on a carbon-paste electrode. The tyrosinase retains its bioactivity when being immobilized by the sol–gel film. Phenolic compounds were determined by the direct reduction of biocatalytically liberated quinone species at 0 mV vs. Ag/AgCl (sat. KCl). The process parameters for the fabrication of the enzyme electrode were optimised. The influence of various experimental variables was explored for optimum analytical performance of the enzyme electrode. The effect of oxygen on the response of the enzyme electrode was evaluated. The sensitivities of the enzyme electrode for catechol, phenol, p-cresol, m-cresol, o-cresol and 2-chlorophenol were 1.53, 1.28, 1.05, 0.687, 0 and 0 A M−1, respectively. The enzyme electrode retained ca. 50% of its activity after 15 days of storage in a phosphate buffer solution at 4°C.

An amperometric mediated glucose sensor has been developed via the sol-gel technique in a new ‘sandwich’ configuration: sol-gel-ferrocene:glucose oxidase (GOx):sol-gel using a carbon paste electrode as the primary electrode. The process parameters for the fabrication of a glucose sensor based on tetramethoxysilane (TMOS) sol-gel thin films utilizing ferrocene as a mediator have been optimized. In the sol-gel matrix, the results demonstrate that GOx still retains its activity, and ferrocene is efficient at shuttling the electrons between the enzyme redox centre and the electrode. Cyclic voltammetric and amperometric measurements have been used to study the response of the glucose sensor, which has a fast response and good reproducibility. The effect of oxygen on the sensor response has been investigated. The selectivity, lifetime and fabrication reproducibility of the sensor have also been evaluated.

The applications of sonochemistry have attracted a great deal of attention. However, conventional chemistry textbooks used in universities and high schools cover traditional chemistry plus thermo,- photo- and electrochemistry. The effect of sound on chemical systems has completely been ignored. Although the mechanisms of many sonochemical reactions remain unresolved, the rapid expansion of knowledge in sonochemistry has already justified its inclusion in present chemistry curricula. Moreover, the interesting and unusual phenomena encountered under sonication conditions can be used for motivation purposes. Furthermore, exploring and equipping students with a new tool for investigating chemistry is also important based on educational principles. This paper examines some chemical systems (in a high school chemistry syllabus) which are affected by sound energy. It is hoped that these sonochemical applications will facilitate the learning of chemistry in terms of cognitive, psychomotor and affective domains.

This is a revisited study on the role of cognitive variables, viz., concept relatedness, idea association, problem translating skill, prior problem solving experience, specific knowledge, and relevant but nonspecific knowledge in problem solving performance in chemistry. Two hundred seventy-nine preuniversity chemistry students from six Singapore junior colleges were involved in this study. This article presents results from the current Singaporean and the previous Australian studies on the relationships between the cognitive variables and problem solving performance in three electrochemistry problems of different degrees of familiarity for comparisons. The two studies confirm that the aforementioned cognitive variables, except concept relatedness, are significant determining variables of problem solving performance. Idea association and problem translating skill are the more important predictors for solving the familiar problem. The five cognitive variables, idea association, problem translating skill, prior problem solving experience, specific knowledge, and relevant but nonspecific knowledge, are all significant predictors of problem solving performance on solving the partially familiar problem. Among them, idea association is the most influential predictor. Problem translating skill is a significant predictor for unfamiliar problems. © 1996 John Wiley & Sons, Inc.

The synthesis and crystal structure of the 1:1 complex formed between triphenyltin chloride and isoquinoline-1-carboxylic acid ([Ph3SnCl:C10H7NO2]) is described. The tin(IV) atom is found to be five coordinate, being bound to three phenyl groups, the chlorine atom, and an oxygen from isoquinoline-1-carboxylic acid. The geometry around the tin atom is that of a trigonal bipyramid, with the three phenyl groups occupying the equatorial positions, and the apical sites taken by the chlorine atom and a carboxyl oxygen from the isoquinoline-1-carboxylic acid. The crystals are triclinic, space group [Formula: see text] with a = 17.932(12) Å, b = 17.935(15) Å, c = 18.686(12) Å, α = 63.16(5)°, β = 81.70(6)°, γ = 68.45(6)°, V = 4986(6)(10) Å3Z = 8, and Dcalc = 1.486 Mg m−3 The final residual is RF = 0.050, on 8375 reflections with Inet > 2.5σ(Inet). Two of the cell dimensions are equivalent and there are four molecular units in the unit cell, so precautions are described for ensuring that correct space-group determination had been made and that some concealed symmetry in the final structure had not been overlooked. Keywords: triorganotin, complex, isoquinoline-1-carboxylic acid, fungicidal activity.

The use of problem-solving in science instruction implies a change in the teacher's role from dispensing content information to encouraging critical reflective thinking in the student. For problem-solving to become an integral part of the science curriculum, teachers must make it the focus of their instruction. This study investigated the extent to which pre-service primary teachers used the problem-solving approach in their science instruction. It also identified the factors affecting their efforts to teach science using this approach. The issues considered are important in whether problem-solving becomes part of the science curriculum, as teaching behaviour influences student learning outcomes.

The effects of power ultrasound on four metal-nonmetal powdered systems: copper-sulphur iron-sulphur, zinc-sulphur and magnesium-sulphur in various solvents, such as hexane and carbon disulphide, are briefly examined here. For each system, a sonication time of 30 min was affected. The sonicated products are analysed by X-ray diffraction, X-ray fluorescence and atomic absorption spectrophotometry to determine their qualitative and quantitative compositions and the percentage yields of the products obtained are then compared and discussed.

A glucose biosensor was fabricated using chitosan film for the immobilization of glucose oxidase (GOX) and mediator in the following “sandwich” configuration:chitosan-ferrocene:GOX:chitosan using a carbon paste electrode as the basic electrode. To prevent loss of immobilized GOX under optimized conditions, the biosensor surface was cross-linked with glutaraldehyde (GA). Despite the multilayer configuration, the biosensor exhibited a relatively fast response (less than 10 s) and a linear response with glucose in the range of 8×10−4 to 1.7×10−2 M. The biosensor retained about 65 % of its original activity after 30 days of storage in a phosphate buffer at 4 °C. Applicability of the biosensor was demonstrated in real samples and the results obtained by this biosensor corroborate well with a classical UV spectrophotometric technique.

Basic Grade 10 inorganic qualitative analysis in Singapore requires students to carry out procedures using chemicals, apparatus and appropriate techniques for which they record their observations and make inferences based on the observations. As students are assessed mainly on their written observations, they focus on getting the correct results and writing ‘standard’ observations. Thus, many students merely follow instructions given in the worksheet and seldom think about or understand the reactions involved especially in terms of what is occurring in these reactions at the sub-microscopic level. To respond to this situation, the authors first designed the Qualitative Analysis Diagnostic Instrument to identify students’ understanding of the reactions involved in qualitative analysis. Secondly, the authors developed the Qualitative Analysis Teaching Package to help students learn qualitative analysis by facilitating their understanding of the sub-microscopic and symbolic level explanations of the macroscopic level experiences of the procedures and reactions involved, as well as the manipulative, observational and inferential skills and thinking processes required. The diagnostic instrument and teaching package are especially important with the imminent change from the current one-off national practical examination to school-based assessment in 2008 with the focus on manipulative, observational, analytical and planning skills.

Kinetin (free base and riboside), which was assumed by many scientists to be a synthetic cytokinin plant growth hormone, has been detected for the first time in the endosperm liquid of fresh young coconut fruits ("coconut water"). To facilitate the study, we developed a sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the identification and quantification of kinetin and kinetin riboside in purified coconut water extract sample. Following a solid-phase extraction of cytokinins in coconut water using C18 columns, the samples were further purified by Oasis MCX columns and analyzed by LC-MS/MS for kinetin and kinetin riboside. Detection by mass spectrometry was carried out using selected reaction monitoring (SRM) mode, by identifying the putative kinetin and kinetin riboside based on their characteristic fragments. Based on a signal-to-noise ratio of 3, the limits of detection in SRM mode were 0.02 microM and 0.005 microM for kinetin and kinetin riboside, respectively. Furthermore, optimal conditions for a baseline chromatographic separation of 18 cytokinin standards by high performance liquid chromatography (HPLC) were developed. The HPLC method had been employed for the confirmation and further fractionation of kinetin in coconut water extracts. The confirmation and fractionation of kinetin riboside was carried out using a further modified HPLC program due to the presence of other interfering material(s) in the sample matrix. Finally, fractions of putative kinetin and kinetin riboside collected from HPLC eluate of coconut water sample were further authenticated by independent capillary zone electrophoresis (CZE) experiment.

A study of the involvement of free oxygen radicals in trapping and digestion of insects by carnivorous plants was the main goal of the present investigation. We showed that the generation of oxygen free radicals by pitcher fluid of Nepenthes is the first step of the digestion process, as seen by EPR spin trapping assay and gel-electrophoresis. The EPR spectrum of N. gracilis fluid in the presence of DMPO spin trap showed the superposition of the hydroxyl radical spin adduct signal and of the ascorbyl radical signal. Catalase addition decreased the generation of hydroxyl radicals showing that hydroxyl radicals are generated from hydrogen peroxide, which can be derived from superoxide radicals. Gel-electrophoresis data showed that myosin, an abundant protein component of insects, can be rapidly broken down by free radicals and protease inhibitors do not inhibit this process. Addition of myoglobin to the pitcher plant fluid decreased the concentration of detectable radicals. Based on these observations, we conclude that oxygen free radicals produced by the pitcher plant aid in the digestion of the insect prey.

This work studied the destruction of various M–EDTA complexes and trace organic pollutants in treated reusable wastewater under advanced oxidation using UV irradiation and ozonation. Effect of dosage of hydrogen peroxide and acidity of reaction matrices on oxidation efficiencies were investigated. The rate constant of mineralization presents a decreasing trend as Fe(III)–EDTA > Fe(II)–EDTA > Al(III)–EDTA > Pb(II)–EDTA > Na(I)–EDTA > Zn(II)–EDTA > Cu(II)–EDTA. The mineralization efficiencies using ozone alone are 15%, 40% and 15% for the water samples after reverse osmosis (RO), microfiltration (MF) and superfiltration (SF) processes, respectively. The presence of hydrogen peroxide in photochemical reaction matrixes can effectively enhance the mineralization of organic carbon species. When 150 mg l−1 of H2O2 was added in the effluents, the mineralization markedly increased to 80%, 92% and 89%, respectively.

The main objective of this paper is to review recent advances in plant drug research and developments in orchid study, in an attempt to provide useful references for plant drug studies. Plants have been used as medicine for millennia. Out of estimated 250 000 to 350 000 plant species identified so far, about 35 000 are used worldwide for medicinal purposes. It has been confirmed by WHO that herbal medicines serve the health needs of about 80 percent of the world's population; especially for millions of people in the vast rural areas of developing countries. Meanwhile, consumers in developed countries are becoming disillusioned with modern healthcare and are seeking alternatives. The recent resurgence of plant remedies results from several factors: 1) the effectiveness of plant medicines; 2) the side effect of most modern drugs; and 3) the development of science and technology. It has been estimated that in the mid-1990s over 200 companies and research organizations worldwide are screening plant and animal compounds for medicinal properties. Actually, several important drugs used in modern medicine have come from medicinal plant studies, eg, taxol/paclitaxel, vinblastine, vincristine, topotecan, irinotecan, etoposide, teniposide, etc. As for drugs derived from orchids, some novel discoveries, both in phytochemical and pharmacological properties, were reported by some universities. However, studies on plants are very limited. Only about a third of the million or so species of higher plants have been identified and named by scientists. Of those named, only a tiny fraction has been studied. Nowadays the linking of the indigenous knowledge of medicinal plants to modern research activities provides a new approach, which makes the rate of discovery of drugs much more effective than with random collection.

Capillary electrophoresis with wall-jet amperometric detection was used to detect kaempferol and its derivatives kaempferol-3-glucoside, kaempferol-3-glucosylrhamnoside and kaempferol-3-(p-coumaroyl)glucoside. The influence of buffer pH on separation was investigated and optimized. With a phosphate buffer at pH 7.5, nearly complete separation of the four kaempferols was achieved according to their different electrophoretic mobilities. The detection potential was also evaluated and optimized. At detection potential of +0.80 V vs. saturated calomel electrode, an amperometric response with high sensitivity and stability was obtained for these four compounds. Detection limit estimated for all the kaempferols examined was less than 1.4 fmol, based on S/N=3. The use of this method for the separation and detection of these compounds present in balsam flowers (Impatiens balsamina) is reported.

An approach based on the use of Planck parameters is used to suggest that the electric charge e is not a fundamental constant.

Chemistry may evoke interest, antipathy, or disinterest in students. Whether students are caught up in the excitement of chemical demonstrations or laboratory experiments, or experiencing difficulties in understanding abstract topics like atomic structure and the mole concept, chemistry is nonetheless undeniably important to both students and the public. Many significant, positive results derive from chemistry, from the discovery of elements to recent spectrometric studies done on Martian soil. Negative results are attributable to chemistry, as well, such as chemical industrial accidents and the use of chemicals as weapons of mass destruction. Chemistry teachers have to prepare students for examinations yet we must also create learning environments and practices that address the affective aspect of students’ learning. By doing this we can fully engage students and maintain their interest and excitement in learning chemistry. Singapore, a small island-state in Southeast Asia, has a school curriculum that...

Most students' introduction to qualitative analysis in the United States occurs in general chemistry courses at college or university; in Australian universities this occurs as part of analytical chemistry courses for chemistry majors. In Singapore, however, students are first introduced to qualitative analysis in grade 10 chemistry (when they are 16 years old), even though the topic is generally considered to be conceptually difficult to understand and there is inadequate time for comprehensive experimental work. Using extensive interviews, this study was designed to identify the sources of these difficulties. Students had difficulty understanding the formation of precipitates and complex salts, and the reactions of acids in qualitative analysis experiments. Many students thought that the formation of precipitates in reactions involving exchange of ions was because of more-reactive ions displacing less-reactive ones, and that ammonia was included in the reactivity series. The students also regarded the f...

Ultrasonic irradiation of copper and lead, separately, in hydrochloric acid shows that mechanistic effects would depend largely on the structural nature of the solid reactants: if the size of a solid reactant is substantially large, microject formation will be the predominant mechanism.

Uses a unit of the activity series of metals to demonstrate the teaching of the interrelationships between chemical concepts by linking new information to previously known material.

The reaction of the ditertiary arsines and phosphines fnfars, fnfos, and fnAsP, (L–L), with Fe(CO)5 at 150° is a superior route to the complexes (L–L)Fe2(CO)6. Two are reported for the first time (L–L = f6fars, f8fars). The complexes react with monodentate and certain potentially bidentate ligands on u.v. irradiation to afford the monosubstituted derivatives L(L–L)Fe2(CO)5 and (L–L)'(L–L)Fe2(CO)5. Spectroscopic studies, in particular magnetically perturbed Mössbauer spectra, indicate that the site of substitution is trans to the FeA—FeB bond and cis to the two group V atoms (on FeA). Disubstitution seems to result in further displacement of CO from either FeA or FeB.

Chlorine nuclear quadrupole resonance frequencies are reported for the compounds [Formula: see text] (n = 2,3,4; Y = H, CH3, C2H5, Si(CH3)3, F. OCH3, N3, NR2, Cl, SCH3, P(C6H5)2, As(CH3)2, Mn(CO)5, π-C5H5Fe(CO)2, but not all combinations). The values range from 38.999 MHz (n = 3; Y = F) to 34.668 MHz (n = 2; Y = π-C5H5Fe(CO)2) and are roughly related to the electronegativity of Y and to the ring size. The mean temperature coefficients of the frequencies lie in the range −0.9 × 10−4 to −8 × 10−4/°K.