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This enhancement of a classic laboratory experiment investigates the kinetic and thermodynamic control of a reaction utilizing ¹H NMR spectroscopy instead of melting point analysis to determine the product distribution. In this experiment, semicarbazide is reacted with cyclohexanone and 2-furaldehyde under varying buffer and temperature conditions to yield semicarbazone derivative products. After ¹H NMR analysis of the products, students compile the class data in a cooperative setting facilitated by graduate teaching assistants. As a result, students are able to analyze a larger data set in this cooperative learning environment in order to describe the product distribution of the reaction on the basis of trends as opposed to using a single data set. The application of 1H NMR spectroscopy to determine the product distribution of the reaction introduces a modern approach to study a well-established example of the kinetic and thermodynamic control of a reaction. [ABSTRACT FROM AUTHOR]

The solution structures of three mixed aggregates dissolved in toluene-d8 consisting of the lithiated amides derived from (S)-N-isopropyl-1-((triisopropylsilyl)oxy)propan-2-amine, (R)-N-(1-phenyl-2-((triisopropylsilyl)oxy)ethyl)propan-2-amine, or (S)-N-isobutyl-3-methyl-1-((triisopropylsilyl)oxy)butan-2-amine and n-butyllithium are characterized by various NMR experiments including diffusion-ordered NMR spectroscopy with diffusion coefficient-formula weight correlation analyses (D-FW) and other one- and two-dimensional NMR techniques. We report that steric hindrance of R1 and R2 groups of the chiral lithium amide controls the aggregation state of the mixed aggregates. With a less hindered R2 group, lithium (S)-N-isopropyl-1-((triisopropylsilyl)oxy)propan-2-amide forms mostly a 2:2 ladder-type mixed aggregate with n-butyllithium. Increase of steric hindrance of the R1 and R2 groups suppresses the formation of the 2:2 mixed aggregate and promotes formation of a 2:1 mixed aggregate. We observe that lithium (S)-N-isobutyl-3-methyl-1-((triisopropylsilyl)oxy)butan-2-amide forms both a 2:2 mixed aggregate and a 2:1 mixed trimer with n-butyllithium. Further increase in the steric hindrance of R1 and R2 groups results in the formation of only 2:1 mixed aggregate as observed with lithium (R)-N-(1-phenyl-2-((triisopropylsilyl)oxy)ethyl)propan-2-amide. [ABSTRACT FROM AUTHOR]

We report the development of isotopic-labeled 13C diffusion-ordered NMR spectroscopy (DOSY) NMR with diffusion coefficient-formula weight (D-FW) analysis and its application in characterizing the aggregation state of methyllithium aggregates and complexes with several widely used diamines. Commercially available 13c-labeled benzene and several easily synthesized 13C-labeled compounds using 13C-labeled iodomethane as the isotopic source are developed as internal references for diflusion-formula weight analysis (D-FW). The technique greatly expands die applicability of DOSY D-FW analysis to a much wider variety of compounds because of isotopic labeling. These results reveal that methyllithium exists as a tetrasolvated tetramer in diethyl ether and exclusively as bis-solvated dirners with chelating diamines [ABSTRACT FROM AUTHOR]

The crystal structure of a mixed aggregate containing lithiated (S)-N-ethyl-3-methyl-1-(triisopropylsilyloxy)- butan-2-amine derived from (S)-valinol and cyclopentyllithium is determined by X-ray diffraction. The mixed aggregate adopts a ladder structure in the solid state. The ladder-type mixed aggregate is also the major species in a toluene-d8 solution containing an approximately 1:1 molar ratio of the lithiated chiral amide to cyclopentyllithium. A variety of NMR experiments including diffusion-ordered NMR spectroscopy (DOSY) with diffusion coefficient-formula (D-FW) weight correlation analyses and other one- and two-dimensional NMR techniques allowed us to characterize the complex in solution. Solution state structures of the mixed aggregates of n-butyl, sec-butyllithium, isopropyllithium with lithiated (S)-N-ethyl-3-methyl-1-(triisopropylsilyloxy)butan-2-amine are also reported. Identical dimeric, laddertype, mixed aggregates are the major species at a stoichiometric ratio of 1:1 lithium chiral amide to alkyllithium in toluene-d8 solution for all of the different alkyllithium reagents. [ABSTRACT FROM AUTHOR]

Solution-state characterization of sec-butyllithium in [D8]toluene was conducted by utilizing a variety of NMR spectroscopic experiments including diffusion-ordered NMR spectroscopy (DOSY) with diffusion-coefficient-formula-weight correlation analyses and other one- and two-dimensional NMR spectroscopic techniques. These results suggest that sec-butyllithium exists primarily as a tetramer/hexamer mixture in hydrocarbon solvents. However, the presence of roughly 2-5 % (by mol ratio) lithium sec-butoxide in both commercially available and laboratory-synthesized sec-butyllithium solutions due to the reaction with adventitious dioxygen will lead to the formation of a 1:5 sec-butoxide/ sec-butyllithium mixed hexamer. A sec-butoxide/ sec-butyllithium mixed octamer will emerge when the proportion of butoxide to butyllithium increases. [ABSTRACT FROM AUTHOR]

The solid state structure of lithiated (S)-N¹,N¹-bis(2-methoxyethyl)-N²,3-dimethylbutane-1,2-diamine, which is a chiral amide base synthesized from (S)-valine was determined by single-crystal X-ray diffraction. The complex in solution state is also characterized by a variety of NMR experiments including diffusion-ordered NMR spectroscopy (DOSY) with diffusion coefficient-formula weight correlation analyses and other one- and two-dimensional NMR techniques by dissolving the crystal in toluene-d8. The crystallography and NMR results suggest that the chiral amide is dimeric in both solid and solution states. [ABSTRACT FROM AUTHOR]

The article presents a study which discusses m/p-cresol-based novolac resin synthesis in di-tert-butyl dicarbonate (t-BOC) using multidimensional nuclear magnetic resonance (NMR) spectroscopy. The study uses Bruker 400 MHz Avance instrument to record the NMR spectra in 400.13 megahertz (MHz) frequency. Results show that polymer macrostructure leads the signal in the NMR spectrum in the range of molecular weights.

Abstract: Attempted two-step postsynthetic modifications (Click reaction and recrystallization) of a dinuclear Zn(II) coordination compound Zn2(OOC–C6H4–N3)4(quinoline)2 lead to the formation of a mononuclear Zn(II) compound – Zn(OOC–C6H4–C2HN3–COOCH3)2(quinoline)·DMSO. In this feasibility study, the relatively low stability of the coordination chromophore around Zn(II) in the starting material is evidenced by Hirshfeld surface analysis and results in the transformation of coordination chromophore during the postsynthetic reaction. Diffusion Ordered Spectroscopy NMR experiments confirmed that the intermediate complex Zn(OOC–C6H4–C2HN3–COOCH3)2 formed by Click reaction exists in the coordinated form in the solution phase despite the loss of the neutral ligand-quinoline. The final product Zn(OOC–C6H4–C2HN3–COOCH3)2·(quinoline)·DMSO with a mononuclear crystal structure was formed by recrystallizing the intermediate with presence of quinoline. [Copyright &y& Elsevier]

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]

Four different chiral diamino diethers synthesized from N-isopropyl valinol or N-isopropyl alaninol were lithiated with n-butyllithium in tetrahydrofuran or diethyl ether. Crystal structures of the dilithiated diamino diethers were determined by X-ray diffraction. Three dilithiated diamino diethers including (2S,2'S)-1,1'-(butane-1,4-diylbis- (oxy))bis(N-isopropylpropan-2-amine) 7, (2S,2'S)-1,1'-(pentane- 1,5-diylbis(oxy))bis(N-isopropylpropan-2-amine) 8, and (2S,2 'S)-l,l'-(heptane -l,7 -diylbis (oxy ))b is (N -isopropyl-3 - methylbutan-2-amine) 9 are dimers, whereas dilithiated (2S, 2'S ) - 1,1 '-(pentane -1,5 -diylbis (oxy ) )bis(N-isopropyl-3- methylbutan-2-amine) 10 is a monomer. The lithium atoms in all crystal structures adopt a nonequivalent coordination protocol and exist in two different environments in which one of the lithium atoms is tetra-coordinated while the other one is tri-coordinated. The solution structures o f the dilithiated diamino diethers are also characterized by a variety of NMR experiments including diffusion-ordered NMR spectroscopy (DOSY) with diffusion coefficient-formula (D-FW) weight correlation analyses and other one- and two-dimensional NMR techniques. [ABSTRACT FROM AUTHOR]

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]

A system consisting of a chiral lithium amide and n-BuLi in tol-d8 solution was investigated with 1H and 13C INEPT DOSY, 6Li and 15N NMR, and other 2D NMR techniques. A mixed 2:1 trimeric complex was identified as the major species as the stoichiometry approached 1.5 equiv of n-BuLi to 1 equiv of amine compound. 1H and 13C INEPT DOSY spectra confirmed this lithium aggregate in the solution. The formula weight of the aggregate, correlated with diffusion coefficients of internal references, indicated the aggregation number of this complex. Plots of log Drel vs log FW are linear (r > 0.9900). 6Li and 15N NMR titration experiments also corroborated these results. These NMR experiments indicate that this mixed aggregate is the species that is responsible for asymmetric addition of n-BuLi to aldehydes. [ABSTRACT FROM AUTHOR]