Mass spectrometry in structural and stereochemical problems—CLXXXVII A study of skeletal rearrangements in chromans by combined 13C and deuterium labeling

Chroman (I), 2,2-dimethylchroman (II), flavan (III) and 2,2-diphenylchroman (IV) were labeled with ¹³C or deuterium at every position of importance. The mass spectra of these labeled compounds make possible a detailed interpretation of some very complex carbon skeleton rearrangements. The combination of deuterium and ¹³C-labeling revealed that loss of CH₃, C₂H₅ and C₇H₇ fragments from chroman (I), 2,2-dimethylchroman (II) and 2,2-diphenylchroman (IV) respectively, occurs by multiple pathways involving aryl or alkyl migrations with little hydrogen randomization prior to fragmentation. Although ejection of C₇H₇ from flavan (III) occurs to a small extent by a route similar to those mentioned above, its [M ? C₇H₇] fragment can also be formed by a pathway involving no phenyl migration but extensive hydrogen scrambling. The validity of the schemes proposed on the basis of the ¹³C labeling data was checked by using them to predict the spectra of the deuterium labeled compounds.     

Jamming and fluctuations in granular drag

We investigate the dynamic evolution of jamming in granular media through fluctuations in the granular drag force. The successive collapse and formation of jammed states give a stick-slip nature to the fluctuations which is independent of the contact surface between the grains and the dragged object, thus implying that the stress-induced collapse is nucleated in the bulk of the granular sample. We also find that while the fluctuations are periodic at small depths, they become "stepped" at large depths, a transition which we interpret as a consequence of the long-range nature of the force chains.     

高碘酸钾法测钢铁及合金中锰的改进建议

试样经酸溶解后,以磷酸-高氯酸混合酸(4 1)或(9 1)氧化至冒烟.在硫酸、磷酸介质中,用高碘酸钾将锰氧化到七价,测其吸光度.     

Student Perceptions of Interest,Learning, and Engagement from an Informal Traveling Science Museum

Informal Science Education (ISE) programs have been increasing in popularity in recent years. The National Research Council has laid out six strands that ISE programs should try to address, including increasing interest, knowledge, and allowing participants to engage in scientific activities. Past research suggests that informal settings can increase interest in science and may lead to knowledge gains. This study examined the impact of a unique ISE program that resembles a traveling museum and offers small‐scale, interactive experiences. Affective outcomes and self‐reported learning outcomes of the students who participated in the program were examined. In general, students reported increases in science interest and some knowledge gains. Students also reported they thought the program allowed them to engage in science. There were differences in student responses based on grade level, with intermediate elementary students more likely to report greater knowledge gains and more likely to see the educational value of the experience. Interestingly, middle school students were more likely to value the social aspects of the experience, another important aspect of ISE. This study provides some insight into the connections between the different ISE strands of informal science education and offers suggestions for future research.     

Effect of Nitrogen Donor Disposition on Topology in Cobalt Isophthalate Coordination Polymers Containing Dipyridylamide Ligands

Cobalt coordination complexes containing a substituted isophthalate ligand and hydrogen‐bonding capable dipyridylamide ligands were prepared hydrothermally and structurally characterized by single‐crystal X‐ray diffraction. {[Co(nip)(3‐pina)]_n ( 1 ) (nip = 5‐nitroisophthalate, 3‐pina = 3‐pyridylisonicotinamide) displays [Co(nip)]_n 1D ribbon motifs with embedded {Co₂(OCO)₂} dimeric units, linked by L‐shaped 3‐pina tethers into a 3D [Co(nip)(3‐pina)]_n coordination polymer network with pcu topology. In contrast, {[Co(nip)(4‐pmina)(H₂O)] · H₂O}_n ( 2 ) (4‐pmina = 4‐pyridylmethylisonicotinamide) manifests a twofold interpenetrated 6⁶ topology diamondoid network. {[Co(meoip)(3‐pina)]_n ( 3 ) (meoip = 5‐methoxyisophthalate) has a dimer‐based 3D pcu network as seen in 1 . [Co(meoipH)₂(4‐pmina)₂(H₂O)₂] ( 4 ) contains neutral coordination complexes linked by hydrogen‐bonding into supramolecular ribbons. Thermal properties of these new solids were also investigated.