Search

Increasingly, the undergraduate chemistry curriculum includes nuclear magnetic resonance (NMR) spectroscopy. Advanced NMR techniques are often taught including two-dimensional gradient-based experiments. An investigation of intermolecular forces including viscosity, by a variety of methods, is often integrated in the undergraduate physical and organic laboratory curricula. An experiment is described that couples advanced NMR techniques with the investigation of viscosity, a physical property based on molecular structure. (Contains 1 table and 5 figures.)

An internal reference correlated diffusion-ordered NMR spectroscopy (DOSY) method is described for calculating the formula weight (FW) of unknown species in different solvents with different concentrations. The guidelines and other factors are discussed for successful application of this internal reference correlated DOSY method.

Your patient, who has been injured or is too ill to work applies for employer-sponsored long-term disability benefits. You provide a supporting medical statement. Surely, the benefits will be approved. [...]

The interactions of energetic materials and polymers have important implications in safety, long-term storage, and performance of explosives and explosive mixtures. Atomic force microscopy was used to investigate adhesion forces at the molecular scale of nine energetic materials, organic explosives and energetic salts, on eleven common polymers (polyethylene, polyvinylalcohol, poly(vinyl chloride), polycarbonate, polystyrene, poly(methyl methacrylate), styrene-butadiene rubber, poly(4-vinyl phenol), poly(2,6-dimethylphenylene oxide), poly(2,6-diphenyl- p-phenylene oxide) (Tenax®), and polytetrafluoroethylene (Teflon®)). Teflon was the least adhesive polymer to all energetic materials, while no distinct trend could be elucidated among the other polymers or energetic materials. [ABSTRACT FROM AUTHOR]

The article presents a science experiment to help college students measure the solution viscosity via diffusion-ordered nuclear magnetic resonance (NMR) spectroscopy. In this experiment, students explore the intermolecular forces including viscosity through numerous methods. Emphasis is on the investigation of the viscosity, a physical property based on molecular structure, using advanced NMR techniques.

The dimeric structure is characterized for a chiral amide base complex consisting of an (S)-N-isopropyl-O-triisopropylsilyl valinol ligand and lithium. The complex is characterized by a variety of NMR techniques, including multinuclear one- and two-dimensional NMR experiments and diffusion ordered NMR spectroscopy (DOSY) as well as diffusion coefficient-formula weight (D-fw) correlation analyses. Spartan calculations are presented which support the structural assignment. This structural characterization leads to an explanation of the behavior and the reactivity of these complexes in solution. [ABSTRACT FROM AUTHOR]

The tetrahydrofuran tetrasolvated dimeric lithium dienolate derived from 2,2,7,7-tetramethyloctan-3,6-dione is characterized in the solid state by X-ray diffraction analysis and in solution by diffusion NMR. This dienolate was reacted with tropanone to yield two new products that are also described. [ABSTRACT FROM AUTHOR]

The utility of recently introduced 6Li diffusion-ordered NMR spectroscopy (DOSY) is demonstrated. 6Li DOSY results can be correlated to 1H data through 2-D 6Li{1H} heteronuclear Overhauser effect NMR spectroscopy (HOESY) experiments. 6Li DOSY quickly confirms 1H DOSY results and allows unambiguous assignment of resonances to specific aggregates. Well known aggregates of lithium-6 n-butyllithium (n-Bu6Li) are examined in deuterated tetrahydrofuran (THF-d8) solution as an example, and to reaffirm the previous literature conclusions about these complexes. [ABSTRACT FROM AUTHOR]

A metastable, polymorphic hexameric crystal structure of lithium pinacolone enolate (LiOPin) is reported along with three preparation methods. NMR-based structural characterization implies that the lithium pinacolate hexamer deaggregates to a tetramer in toluene but retains mainly the hexameric structure in nonaromatic hydrocarbon solvents such as cyclohexane. Moreover, the presence of a small amount of lithium aldolate (LiOA) dramatically influences the aggregation state of LiOPin by forming a mixed aggregate with a 3:1 ratio (LiOPin 3 ·LiOA).

Development and application of physically separated references for aqueous (1)H DOSY diffusion coefficient-formula weight (D-FW) correlation analysis is reported. Commercially available biological buffers (Tris and HEPES) and a water-soluble alcohol (tert-butanol) were used as physically separated references for a Ru and a Mn complex in D(2)O. This extension of DOSY D-FW analysis expands its applicability to a wide variety of water-soluble molecules or metal complexes, with particular application to green chemistry.

The development of (6)Li diffusion-ordered NMR spectroscopy (DOSY) is reported. This technique is applied to (6)Li organometallic complexes. (6)Li DOSY provides a facile means of identification of peaks in the (6)Li spectrum, as well as evidence of mixed aggregates based on relative diffusion coefficients. (6)Li data is correlated to (1)H diffusion experiments through (6)Li{(1)H} HOESY and/or (1)H{(6)Li} HMBC experiments to obtain formula weight information of Li aggregates.

The development of (31)P DOSY NMR with diffusion coefficient-formula weight (D-FW) analysis is reported. Commercially available trialkyl phosphine internal references were used in a model system to establish the molecular weight of a phosphorous containing organolithium compound. The feasibility of (31)P DOSY D-FW studies is established. This extension of DOSY D-FW analysis expands its applicability to solution structure studies of a wide variety of compounds.

Formula weight (FW) information is important to characterize the composition, aggregation number, and solvation state of reactive intermediates and organometallic complexes. We describe an internal reference correlated DOSY method for calculating the FW of unknown species in different solvents with different concentrations. Examples for both the small molecule (DIPA) and the organometallic complex (aggregate 1) yield excellent correlations. We also found the relative diffusion rate is inversely proportional to the viscosity change of the solution, which is consistent with the theoretical Stokes-Einstein equation. The accuracy of the least-squares linear prediction r(2) and the percentage difference of FW prediction are directly related to the density change; greater accuracy was observed with decreasing density. We also discuss the guidelines and other factors for successful application of this internal reference correlated DOSY method. This practical method can be conveniently modified and applied to the characterization of other unknown molecules or complexes.