Further Development and Validation of the Teaching Science as Inquiry (TSI) Instrument

The purpose of this study was to further develop and validate the Teaching Science as Inquiry (TSI) Instrument, an instrument designed to measure the self‐efficacy beliefs of preservice teachers in regards to the teaching of science as inquiry. Based on the validation processes and the associated data analysis, the TSI demonstrates continued content and construct validity with high internal reliability when used with prospective elementary science teachers.     

High temperature arc studies of infrared radiation from boron and tungsten oxides

Long wavelength infrared emission spectra from boron and tungsten compounds in air were obtained in a d.c. arc jet at 3000–6000°K for the wavelength range 1·2–24 μm. Absolute vibrational band intensities were measured for WO, WO₂, WO₃, BO, BOF and BF₃ molecules. Several unidentified bands were observed and are discussed.     

Use of 73Ge NMR spectroscopy for the study of electronic interactions

The lack of understanding of the structural and electronic factors that affect the often difficult to observe germanium resonance has been a major deterrent to studies of bonding interactions at germanium. We utilized the symmetrical system GeR 4 to determine what structural factors inherent in the R group affect the shape and position of the (73)Ge resonance. The (73)Ge resonances of symmetrical tetrakis germanium compounds of the type GeR 4 (R = alkyl, aryl), GeX 4 (X = F, Cl, Br, I), Ge(OR) 4 (R = alkyl, methoxyalkyl, dimethylaminoalkyl), Ge(NR 2) 4 (R = alkyl), and Ge(SR) 4 (R = alkyl, dimethylaminoalkyl) were examined for evidence of intramolecular coordination. Although many of these compounds have sharp resonances due to idealized tetrahedral symmetry with relatively long relaxation times, others have broad or no observable resonances due to fast quadrupolar relaxation. We hypothesize that the perturbation of symmetry by even weak Lewis interactions or conformational changes causes broadening of the resonance before the interaction can become sufficiently strong to cause the significant low-frequency shift generally associated with hypercoordination in most nuclei. Intermolecular coordination to GeCl 4 is believed to be responsible for the low-frequency shifts in (73)Ge resonances and the associated changes in peak widths in mixtures with bases such as tributylphosphine oxide (TBPO) and triethylphosphine oxide (TEPO). Adduct formation with these bases is confirmed by broad (31)P resonances that are resolved into five peaks at -40 degrees C. The exchange-broadened resonances due to the 1:1 and 1:2 TEPO adducts are also observed at -40 degrees C in the (73)Ge spectrum. Thus, relatively strong bonding to the germanium in GeCl 4 results in both low-frequency shifts and broadening of the resonance. The broad (73)Ge resonances that occur in some compounds may be in part due to exchange as well as quadrupolar relaxation.     

Metal Transition in Sodium–Ammonia Nanodroplets

The famous nonmetal‐to‐metal transition in Na–ammonia solutions is investigated in nanoscale solution droplets by photoelectron spectroscopy. In agreement with the bulk solutions, a strong indication for a transition to the metallic state is found at an average metal concentration of 8.8±2.2 mole%. The smallest entity for the phase transition to be observed consists of approximately 100–200 solvent molecules. The quantification of this critical entity size is a stepping stone toward a deeper understanding of these quantum–classical solutions through direct modeling at the molecular level.     

1H, 13C, and 73Ge NMR spectral analysis of substituted aryltrimethylgermanes

NMR chemical shifts of 1H, 13C, and 73Ge are reported for a series of monosubstituted aromatic trimethylgermanes of the type XC6H4Ge(CH3)3; X = p-N(CH3)2, p-OCH3, p-OC2H5, p-C(CH3)3, p-Si(CH3)3, p-Ge(CH3)3, p-Sn(CH3)3, p-CH3, m-CH3, -H, m-OCH3, p-Cl, p-Br, m-F, m-CF3, p-CF3, o-OCH3, and o-CH3. The relatively narrow 73Ge resonances show a strong correlation with Hammett sigma constants, with a correlation coefficient of 0.976 and 0.876 for 73Ge chemical shifts in meta- and para-substituted derivatives, respectively. The 13C chemical shifts of the methyl carbons bonded to germanium also display a relationship, with correlation coefficients of 0.904, 0.993, and 0.911 for para-, meta- and all derivatives, respectively. Comparisons of the Hammett plots for the homologous series XC6H4M(CH3)3; M = C, Si, Ge, Sn, show that, in general, correlation coefficients decrease while slopes increase significantly down the group, presumably reflecting the corresponding increase in chemical shift range of the group 14 atom. The Hammett constant derived for the p-Ge(CH3)3 group of +0.13 compares with the NMR-derived constants of -0.12 for p-C(CH3)3, +0.14 for p-Si(CH3)3, and -0.14 for p-Sn(CH3)3. The indication of electron release by carbon and tin can be rationalized through traditional hyperconjugative arguments for carbon and by the low electronegativity and consequent inductive effect of tin. The small electron attraction suggested by the positive constants for silicon and germanium can be simply, and perhaps naively, attributed to pi-acceptor interactions with the benzene ring.     

A new model for the rationalization of the thermal behavior of carbonated apatites

A new model for the location and distribution of carbonate ions in carbonated apatite was used to assign the IR spectra of A- and AB-carbonated apatites. The percentage of total carbonate as measured by the mass loss in the TGA of these compounds is in good agreement with the percentage obtained by combustion analysis. The decomposition of pure A-type carbonate appears at temperatures of 985–1123 °C, whereas the decomposition of AB-type carbonated apatites occurs in the range of 600–800 °C. This difference is attributed to changes in the environment of channel carbonate brought about by B-type substitution of carbonate for phosphate. In the presence of sodium ions, the channel is changed by substitution of sodium for calcium in order to accommodate the difference between the charge of the carbonate and phosphate ions. A thermodynamic cycle is introduced to rationalize the differences in decomposition temperatures of A- and B-type carbonate. Preferential loss of B-type carbonate upon heating to 600 °C also suggests the migration of B-type carbonate to A-sites.

     

Phosphineborane analogs of trimethylsilyl amides

The reaction of (CH₃)₂(BH₃)PCl with the lithium salts of acetamide, N-methyl acetamide, and N-methyl formamide produced the N(CH₃)₂(BH₃)P-monosubstituted amides. Attempts to employ the same procedure for the preparation of the bis-acetamide, the acetanilide and the N-methyl benzamide derivatives were unsuccessful. Variable temperature NMR spectroscopy revealed the presence of rotational isomers for the formamide with a population of 0.85 for the major rotamer which on the basis of the ³¹P-formyl proton coupling constants was assigned the structure where the (CH₃)₂(BH₃)P group is trans to carbonyl oxygen. The free energies of activation were determined to be 16.2 and 17.3 kcal/mol. For the other derivatives only one isomer could be detected down to—60°C. The compounds are similar to the trimethylsilyl analogs in structure and rotational populations, but the lower rotational barrier in the phosphineborane formamide derivative suggests a greater destabilization of the polar ground state amide resonance structure by the formal positive charge on phosphorus.     

Structure and dynamics of t-butyldimethylsilyl amides

A series of N-alkyl- and N-aryl-t-butyldimethylsilyl amides have been prepared by amination and their structures determined by IR and NMR spectroscopy. Like their trimethylsilyl counterparts, the N-alkyl derivatives exist as amides while the N-aryl derivates exist as amide/imidate mixtures. The percentage of imidate and the free energies of activation for the imidate/amide exchange in the aryl derivatives are greater than those in the trimethylsilyl derivatives. The barriers to rotation in the amide form of the aryl derivatives are similar to those of the trimethylsilyl derivatives. The barrier for rotation in t-butyldimethylsilyl-N-methyl formamide, however, is lower than that of the trimethylsilyl derivative. Isomer ratios and free energies of activation are rationalized in terms of the steric effect of the t-butyl group.     

Chain epimerization during propylene polymerization with metallocene catalysts: mechanistic studies using a doubly labeled propylene

The mechanisms of chain epimerization during propylene polymerization with methylaluminoxane-activated rac-(EBTHI)ZrCl(2) and rac-(EBI)ZrCl(2) catalysts (EBTHI = ethylenebis(eta(5)-tetrahydroindenyl); EBI = ethylenebis(eta(5)-indenyl)) have been studied using specifically isotopically labeled propylene: CH(2)=CD(13)CH(3). These isospecific catalysts provide predominantly the expected [mmmm] pentads with [minus signCH(2)CD(13)CH(3)(-)] repeating units ((13)C NMR). Under relatively low propylene concentrations at 50 and 75 degreesC, where stereoerrors attributable to chain epimerization are prevalent, (13)C NMR spectra reveal (13)C-labeled methylene groups along the polymer main chain, together with [CD(13)CH(3)] units in [mmmr], [mmrr], and [mrrm] pentads and [CH(13)CH(3)] units in [mmmmmm] and [mmmmmr] heptads, as well as [mrrm] pentads. The isotopomeric regiomisplacements and stereoerrors are consistent with a mechanism involving beta-D elimination, olefin rotation and enantiofacial interconversions, and insertion to a tertiary alkyl intermediate [Zr-C(CH(2)D)((13)CH(3))P] (P = polymer chain), followed by the reverse steps to yield two stereoisomers of [Zr-CHDCH((13)CH(3))P] and [Zr-(13)CH(2)CH(CH(2)D)P], as well as unrearranged [Zr-CH(2)CD((13)CH(3))P]. The absence of observable [-CH(2)CH(13)CH(2)D-] in the [mrrm] pentad region of the (13)C NMR spectra provides evidence that an allyl/dihydrogen complex does not mediate chain epimerization.     

Reactivity of small Mo(x)Oy- clusters toward methane and ethane

The reactions of Mo2Oy- suboxide clusters with both methane and ethane have been studied with a combination of mass spectrometry, anion photoelectron spectroscopy, and density functional theory calculations. Reactions were carried out under "gentle" and "violent" conditions. For methane, a number of products appeared under the gentler source conditions that were more logically attributed to dissociation of Mo2Oy- clusters upon reacting with methane to form MoCH2-, Mo(O)CH2-, and HMo(O2)CH3-. With ethane, products observed under the same gentle conditions were Mo(O)C2H2-, Mo(O)C2H4-, Mo(O2)C2H4-, and Mo(O2)(C2H5)2-. As expected, more products were observed when the reactions were carried out under violent conditions. The photoelectron spectra obtained for these species were compared to calculated adiabatic and vertical electron affinities and vibrational frequencies, leading to definitive structural assignments for several of the products.