NMR spectroscopy monitoring

Infrared (FT-IR, NIR) spectroscopy Solid-state NMR spectroscopy Monitor structure (polymorphs and solvates), conformation, and intermolecular environment of crystals... 

Wollweber43 has extended this reaction to aliphatic y-keto acids. The products he obtained are identical to 75 except that the 8a-aryl substituent has been replaced with an aliphatic group. Wollweber et al.n have also studied the course of the above reaction using NMR spectroscopy. Monitoring the condensation of 76 with 77, they observe the aminal ester (78) intermediate after 15 minutes. This intermediate slowly disappears as product 79 is formed [Eq. (22)]. 

Muller D. et al (1992) Progress in the Al MAS NMR spectroscopy monitoring the hydration of calcium aluminate cements, in Proceedings 9th ICCC, New Delhi, Vol. 6,... 

Homogeneously and heterogeneously catalyzed esterification kinetics butyl acetate esterification—online H NMR spectroscopy monitoring of rapidly changing compositions offered a fast and reliable analysis of all reaction components. 

Vargas M A, Cudaj M, Hailu K, Sachsenheimer K, Guthausen G. Online low-field H NMR spectroscopy monitoring of emulsion polymerization of butyl acrylate. Macromolecules 2010 43 5561-5568. 

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

To establish a mechanism for the formation of 33, the reaction has been monitored by H-NMR spectroscopy (91CB2013).Tlie basicity of the azine is a rate-determining effect as well as a steric hindrance. Pyridine is more reactive than pyrimidine. 2-Substituted pyridines do not give the corresponding salts. 

MeOH with a Hannovia UV lamp in 1973 (73TL2451). Monitoring with H NMR spectroscopy, only two among many products appeared to contain an ethoxy group. After several separations, 3-ethoxy-2-phenylindole (147, 12%), 2-phenylindole (149, 35%), and an unknown ethoxy-containing 2-phenylindole (unknown 148, 3%) were isolated (Scheme 23). 

Treatment of quinoline with ethylene oxide gave oxazolo[3,2-u]quinoline 597 whereas 2-methylquinoline did not react with ethylene oxide (79JOC285). The oxazolidine 597 is labile as monitored by H NMR spectroscopy its colorless solution in CDCI3 became dark red within several hours (Scheme 100). 

A number of different methods to monitor the amount of methylimidazole left in a final ionic liquid are known. NMR spectroscopy is used by most academic groups, but may have a detection limit of about 1 mol%. The photometric analysis described by Holbrey, Seddon, and Wareing has the advantage of being a relatively quick method that can be performed with standard laboratory equipment [13]. This makes it particularly suitable for monitoring of the methylimidazole content during commercial ionic liquid synthesis. The method is based on the formation and colorimetric analysis of the intensely colored complex of l-methylimidazole with cop-per(II) chloride. 

In this context it is important to note that the detection of this land of alkali cation impurity in ionic liquids is not easy with traditional methods for reaction monitoring in ionic liquid synthesis (such as conventional NMR spectroscopy). More specialized procedures are required to quantify the amount of alkali ions in the ionic liquid or the quantitative ratio of organic cation to anion. Quantitative ion chromatography is probably the most powerful tool for this kind of quality analysis. 

The loss of sulfur can also be monitored by H NMR spectroscopy, allowing a kinetic analy-sis12,9 and a determination of the half-lives of various substituted 1-benzothiepins,1 including halo derivatives.9... 

A solution of 1.0 g (33 mmol) of the mixture of heptofuranoside diastereomers (14) in 5 ntL of THE is stirred in an ice-water bath. 3.4 mL of 1 M soln ofTBAF (3.4 mmol) in THF are added, and Ihe reaction is monitored by TLC (CHCI,/CH, OH, 9 1). After ca. 15 min, the reaction mixture is carefully neutralized with dil sulfuric acid, then diluted with water and extracted with CHC13. The extract is dried over Na,S04 and concentrated to give an off-white solid which is a single stereoisomer (by NMR spectroscopy). Column chromatography gives the inositol as a white solid yield 0.61 g (70%) mp 186-187 C (benzene/CH,OH) [a]D + 118 (c = 03, CH, OH). 

A careful investigation of the reaction kinetics and detailed trapping experiments allow the conclusion that in this case a a-bond metathesis reaction mechanism applies. The polymerization reaction of PhSiH3 by CpCp Hf(SiH2Ph)Cl has been monitored by H-NMR spectroscopy. The data k(75 °C) = 1.1(1) x 10-4 M 1 s AH = 19.5(2) kcal mol" AS = -21(l)euandkH/fcD = 2.9(2) (75 °C) are in good agreement with the proposed mechanism with a metallacycle as transition state [164],... 

The NMR characteristics of the bromonium ion triflate prove to be interesting in that the proton NMR spectrum of a 1 1 mixture of parent olefin and bromonium ion at room temperature is an average of those of the two isolated species. This suggests that there is a rapid site exchange of the Br+ between the ion and olefin. The phenomenon can be most simply studied by NMR spectroscopy. An approximately 100 mM solution of the ion in CD2C12 held at - 80°C was treated with small aliquots of Ad=Ad, the NMR spectrum was monitored after each addition. At zero added Ad=Ad, the spectrum of the ion consists of a seven line pattern indicative of a species (eqn. 3, 5a) having two perpendicular planes of symmetry that pass, respectively, through the three heavy atoms of the bromonium... 

EPR investigations are necessarily carried out in frozen solution at low temperature. Room temperature binding of thiols to FeMoco has been monitored by F NMR spectroscopy using /J-CF3C6H4S as the reporter ligand. These experiments revealed that the binding of thio-late is characterized by a dynamic equilibrium between the FeMoco and thiolate (159) and that cyanide and methyl isocyanide can bind to isolated FeMoco complexed with thiol (160). 

The reactions depicted in Eq. (1) are suitable for calorimetric investigations since they proceed rapidly and quantitatively as monitored by NMR. spectroscopy. The. solution calorimetric protocol has been described elsewhere." The enthalpy values were determined by anaerobic solution calorimetry in THF at 30 C by reacting 4 equivalents of each carbene with one equivalent of tetramer. The results of this study are presented in Table I. 

The reactions of MeMn(CO)5 with various phosphines and phosphites (L) to give/ac-MeCOMn(CO)3L2 and/or wicr(L srrflMi)-MeCOMn(CO)3L2 have been monitored by NMR spectroscopy 166). Sterically demanding L s promote formation of the meridional over the facial isomer. Interestingly, the meridional acetyls decarbonylate more easily than their facial counterparts, perhaps owing to a weaker Mn—CO bond cis to COMe in the former. 

The most convenient tool for the characterisation of NHCs is NMR spectroscopy, in particular C H NMR. As a case study, the carbenes IPr and SIPr, and their corresponding salts IPr HCl and SIPr HCl were chosen. As described above (Scheme 1.2), free carbenes are often obtained by deprotonation of the corresponding salt. The best diagnostic tool to observe the salt deprotonation, and thus indirectly monitor the carbene formation, is H NMR spectroscopy, by means of the disappearance of the characteristic acidic proton resonance. The signal corresponding to the latter (ff) is largely shifted downfield (typically 8-12 ppm) and disappears upon deprotonation (Fig. 1.5). 

In order to achieve a true comparison between both catalytic systems, colloidal and molecular, which display very different reaction rates, a series of experiments were carried out with the homogeneous molecular system, decreasing the catalyst concentration in the studied allylic alkylation reaction. The reaction evolution is monitored taking samples at different reaction times and analysing each of them by NMR spectroscopy (to determine the conversion) and HPLC chromatography with chiral column (to determine the enantioselectivity of I and II). For molecular catalyst systems, the Pd/substrate ratio was varied between 1/100 and 1/10,000. For the latter ratio, the initial reaction rate was found comparable to that of the colloidal system (Figure 2a), but interestingly the conversion of the substrate is quasi complete after ca. 100 h in... 

M.E. Amato, G. Ansanelli, S. Fisichella, R. Lamanna, G. Scarlata, A. P. Sobolev, A. Segre 2004, (Wheat flour enzymatic amylolysis monitored by in situ H-l NMR spectroscopy),/. Agric. Food. Chem. 52, 823-831. 

Although limited by sensitivity, chemical reaction monitoring via less sensitive nuclei (such as 13C) has also been reported. In 1987 Albert et al. monitored the electrochemical reaction of 2,4,6-tri-t-butylphenol by continuous flow 13C NMR [4]. More recently, Hunger and Horvath studied the conversion of vapor propan-2-ol (13C labeled) on zeolites using 1H and 13C in situ magic angle spinning (MAS) NMR spectroscopy under continuous-flow conditions [15]. 

K. Albert, E.-L. Dreher, H. Straub, A. Rieker 1987, (Monitoring electrochemical reactions by 13C NMR spectroscopy), Magn. Reson. Chem. 25, 919. 

M. Maiwald, H. H. Fischer, Y.-K. Kim, K. Albert, H. Hasse 2004, (Quantitative high-resolution on-line NMR spectroscopy in reaction process monitoring), /. Magn. Reson. 166, 135. 

Hyperpolarized 129Xe NMR Spectroscopy, MRI and Dynamic NMR Microscopy for the In Situ Monitoring of Gas Dynamics in Opaque Media Including Combustion Processes... 

Acknowledgments Several review articles cover in much greater details numerous NMR applications that have been reported in the past years on the use of NMR spectroscopy in the drug discovery process and to monitor target-ligand interactions. The author apologizes if he was unable to mention properly all this work within the limited space of this article. 

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