Polymerization of propylene with catalysts derived from unbridged 2-arylindene metallocenes leads to elastomeric, low-tacticity polypropylenes. The polymerization behavior these conformationally dynamic catalyst systems is interpreted in terms a multistate mechanism where the enchains monomer both stereoselective and nonstereoselective conformations during lifetime single polymer chain. structure properties polypropylenes depend sensitively on metallocene conditions (temperature, pressure,...

A concurrent tandem catalytic methodology has been developed for the hydrodehalogenation of aryl bromides and chlorides. The first step cycle, halogen exchange, produced yields 84–97% from using 5 mol % CuI catalyst, 10 N,N′-dimethylcyclohexane-1,2-diamine (1), 2 equiv NaI in acetonitrile under microwave radiation at 100 °C 0.5–1.5 h. same reaction chlorides appeared to be equilibrium-limited after 1 hour 200 (yields 5–44%). Both were hydrodehalogenated 12–87% yield 20 CuI, 1.5 diamine 1,...

Self-assembled cylindrical capsule 1 is reversibly formed from dimerization of two tetraimide resorcinarenes. Studies guest exchange involving host reveal a mechanistic continuum for that depends on the structure guest. Kinetic and dynamic NMR measurements demonstrate direct displacement one by another. Surprisingly, in case benzene pairwise encapsulation p-xylene, incoming occupies same half as outgoing benzene. As size guests increases, solvent-bridged intermediates determine rates; empty...

The four-component ensemble comprising CB[6], β-CD, and guests 1 2 forms complexes CB[6]·1H+ β-CD·2 at pH < 7 but swaps partners forming CB[6]·2 β-CD·1 > 13. intermolecular nature of the switching process suggests application as a basis for stimuli-responsive reconfigurable systems.

This study examined similarities and differences in approaches reported by general chemistry students performing at different achievement levels. The population consisted of freshmen enrolled a required year-long course the U.S. Naval Academy. Students first second semesters were surveyed using modified version published Approaches Study Skills Inventory for (ASSIST) referred to as M-ASSIST (Modified Inventory). Responses items associated with deep or surface studying three levels (A/B, C,...

Classroom observation data using tools such as the Observation Protocol for Undergraduate STEM (COPUS) are frequently collected in instructional settings large-scale research studies and program assessment. While COPUS may be provided to instructors, it is often with little or no guidance on how can used inform teaching practice. This communication designed serve a guide chemistry instructors understand from their course, facilitate engagement results, provide strategies making meaningful...

A national survey of chemists (n = 174) explored the self-reported format and focus postsecondary inorganic chemistry instructional laboratory curricula. Multiple course formats were observed, including stand-alone courses, instruction as a component multidisciplinary course, absence an experience. Additionally, types synthetic, characterization, purification methods, well professional skills addressed in surveyed varied greatly. The results this work have direct implications "current state...

We report the synthesis of a variety titanium complexes that contain (Et3SiNCH2CH2)3N, (C6F5NCH2CH2)3N, or (Me3SiNCH2CH2CH2)3N ligands. Complexes in first category include [(Et3SiNCH2CH2)3N]TiCl, [(Et3SiNCH2CH2)3N]Ti(OTf), and [(Et3SiNCH2CH2)3N]Ti(t-Bu). second [(C6F5NCH2CH2)3N]TiX (X = Cl, Br, I, OTf) [(C6F5NCH2CH2)3N]TiR (R Me, Et). third [(Me3SiNCH2CH2CH2)3N]TiCl [(Me3SiNCH2CH2CH2)3N]TiCH3. In an X-ray study was shown to coordinated amino nitrogen TiN2C3 rings were puckered...

Autocatalysis and chemical amplification are characteristic properties of living systems, they give rise to behaviors such as increased sensitivity, responsiveness, self-replication. Here we report a synthetic system in which unique form compartmentalization leads nonlinear, autocatalytic behavior. The compartment is reversibly formed capsule reagent sequestered. Reaction products displace the from into solution reaction rate accelerated. resulting self-regulation sensitive highly selective...

The association between student motivation and learning, changes in across a course, were evaluated for students enrolled one-semester foundation-level inorganic chemistry courses at multiple postsecondary institutions the United States. Academic Motivation Scale Chemistry (AMS-Chemistry) Foundations of Inorganic American Chemical Society Exam ( i.e. , content knowledge measure) used this study. Evidence validity, reliability, longitudinal measurement invariance data obtained from...

A kinetic model was developed to describe the propylene polymerization behavior of fluxional, two-state metallocene catalysts. In particular, pentad and molecular weight distributions can be described as well other parameters interest, such fraction crystallizable sequences isotactic sequence length distribution, in terms fundamental constants conditions that pertain these catalyst systems. The used an attempt two, prototypical, fluxional systems, (2-PhInd)2ZrCl2/MAO (1)...

The kinetics of propylene polymerization in toluene solution by bis(2-phenylindenyl)zirconium dichloride/methylaluminoxane at 20 °C were investigated. As the structure and properties elastomeric polypropylenes produced these catalysts depend sensitively on reaction conditions, a detailed study was carried out to evaluate influence parameters behavior. Studies solubilities mass-transfer rates reveal that dissolved atactic polypropylene has little effect solubility but influences rate into...

Metallocene catalysts derived from bis(2-arylindenyl)zirconium dichloride yield elastomeric stereoblock polypropylene. A study of the steric and electronic effects varying 4-substituent bis(2-(4-R-C6H4)indenyl)zirconium [(1 RH, 2 RMe, 3 REt, 4 RnBu, 5 RtBu, 6 RSiMe3, 7 RCF3, 8 RCl)] on propylene polymerization at 25, 50, 75 psig bulk revealed that behavior these is not strongly influenced by nature substituent in 4-position 2-aryl substituent. Examinations microstructure...

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication the EditorNEXTCondensation of Arylboroxine Structures on Lewis Basic Copolymers as a Noncovalent Strategy toward Polymer FunctionalizationPeter M. Iovine, Matthew N. Fletcher, and Shirley LinView Author Information Department Chemistry Biochemistry, University San Diego, 5998 Alcala Park, California 92110, Chemistry, United States Naval Academy, 572 Holloway RD, Annapolis, Maryland 21402 Cite this: Macromolecules 2006, 39,...

ADVERTISEMENT RETURN TO ISSUEPREVArticleCreating Customized, Relevant, and Engaging Laboratory Safety VideosMichael L. Matson , Jeffrey P. Fitzgerald Shirley Lin View Author Information Department of Chemistry, United States Naval Academy, Annapolis, MD 21402Cite this: J. Chem. Educ. 2007, 84, 10, 1727Publication Date (Web):October 1, 2007Publication History Received3 August 2009Published online1 October 2007Published inissue 1...

Abstract The antimicrobial activity of cationic N ‐dodecyl‐ ‐methylpolyethylenimine (PEI+) against S. aureus , A. baumannii and E. coli was evaluated when the polymer applied as a coating to various surfaces using paint‐like procedure. Antimicrobial PEI+ function time determined an assay for long‐term survival involving placement single drops bacterial concentrations on dry surfaces. These data were compared with method where bacteria by spraying incubated overnight under agar. PEI+‐coated...

The percentage of students choosing the correct answer (PSCA) on 17 multiple-choice algorithmic questions taken from general chemistry exams is analyzed. PSCAs for these varied 47 to 93%, and a decrease 4.5% in PSCA was observed with each additional step algorithm required solving problem (R2 = 0.80). Variants subset were also examined reveal effect making changes particular question ability choose answer.

A microwave-assisted, copper-catalyzed concurrent tandem catalytic (CTC) methodology has been developed for the cyanation of aryl chlorides, where chloride is first converted to an iodide via halogen exchange and subsequently transformed nitrile. variety chlorides were nitriles in 44–97% yield using 20 mol % CuI, 40 N,N'-cyclohexane-1,2-diamine, 1.2 equiv KCN acetonitrile at 200 °C after 1–2 h. The same copper/ligand system served as a multifunctional catalyst both steps process. Unlike our...

A concurrent tandem catalytic (CTC) methodology has been developed for the amidation of aryl chlorides where chloride is first converted to an iodide via halogen exchange and subsequently transformed into amide. variety were amides in up 85% isolated yield using 20 mol % CuI, 60 N,N′-cyclohexane-1,2-diamine, 2.2 equiv K2CO3, 1.05–1.5 amide acetonitrile at 200 °C after 0.75–1 h. The same copper/ligand system served as multifunctional catalyst both steps process with present substoichiometric...

ACS Examinations provide a lens through which to examine historical changes in topic coverage via analyses of course-specific examinations. This study is an extension work completed previously by the Exams Research Staff and collaborators general chemistry, organic physical chemistry explore content principal courses postsecondary curriculum. In this study, we consider how inorganic has varied over 55-year period since first Examination was released 1961. A total 860 items evaluated on basis...

Students with an insufficient amount of time to study are becoming more prevalent in the general college population as many who enroll have competing responsibilities (full-time jobs, childcare, etc.). Such students likely choose resources that they consider be both effective and efficient. at U.S. Naval Academy (USNA) constrained their because required course load institutional daily requirements. The purpose this was survey which USNA for studying look difference choice relation different...

Catalysts of the type bis(2-(3,5-R2C6H3)indenyl)zirconium dichloride/MAO (2, R = H; 3, CF3) were investigated for regioregularity monomer insertion in bulk propene polymerization and compared to isospecific catalyst rac-(ethene)bis(indenyl)zirconium (1). The amount regioirregular insertions range 0.1−0.5 mol % followed trend 2 < 3 1. Comparison polymerizations presence absence hydrogen revealed a 4−10-fold increase productivity catalysts but only slight with For 2,1-erythro internal...

Acid–base titration concepts and experiments are ubiquitous, yet challenging, aspects of the general chemistry curriculum. Most courses include at least one acid–base laboratory experiment, though focus is often on determining concentration, pKa, or molar mass an analyte rather than details interpreting a curve more broadly. This article describes transformation single-period, traditional confirmation experiment into multiweek, guided-inquiry capstone experience investigating phosphate...