NMR spectroscopy reaction

Using 15N-edited one-dimensional H-NMR spectroscopy and 2D [1H,15N] HMQC-NMR spectroscopy, reactions between 15N-labelled cis-PtCl2(NH3)2 and guanosine 5 -monophosphate (5 -GMP) have been studied in aqueous solutions [17]. The short-lived aqua-chloro intermediate is detectable during the early stages, followed by the formation of the mono- and... 

Oxidation of ]V-MeTTPFenCl (46, 52). Catalytic alkene oxidation by iron N-alkylporphyrins requires that the modified heme center can form an active oxidant, presumably at the HRP compound I level of oxidation. To show that iron N-alkyl porphyrins could form highly oxidized complexes, these reactive species were generated by chemical oxidation and examined by NMR spectroscopy. Reaction of the (N-MeTTP)FenCl with chlorine or bromine at low temperatures results in formation of the corresponding iron(III)-halide complex. Addition of ethyl- or t-butyl-hydroperoxide, or iodosylbenzene, to a solution of N-MeTTPFenCl at low temperatures has no effect on the NMR spectrum. However, addition of m-chloroperoxybenzoic acid (m-CPBA) results in the formation of iron(III) and iron(IV) products as well as porphyrin radical compounds that retain the N-substituent. 

An investigation of dynamic molecular processes that occur in seminal fluid has been undertaken using H NMR spectroscopy. Reactions that could be followed included hydrolysis of phosphorylcholine and nucleotides and zinc complexation. ... 

NMR Experiments. For monitoring by NMR spectroscopy, reactions of the nitroaromatics with nucleophiles were generally carried out in situ by addition of the appropriate reagent to a (CD3)2SO solution of the given nitroaromatic (DNBF, 0.4 M PiDNBT, 0.1 M). The reagents were applied to the sides of the NMR tube, which was then capped and shaken vigorously. Spectra were recorded at given time intervals on a JEOL MH-100 spectrometer with tetramethylsilane as the internal standard. 

Reactions of substituted prop-2-ynyl lithium compounds can similarly give acetylenic and allenic products. Huynh and Linstrumelle prepared the lithium acetylide 11 and confirmed its structure by NMR spectroscopy. Reaction with propylene oxide then gave a mixture of 12 (45%) and 13 (55%), showing that both organo-lithium species can react to give either allenic or acetylenic products. 

Furan reacts vigorously with chlorine and bromine at room temperature to give polyhalogenated products, but does not react at all with iodine. More controlled conditions can give 2-bromofuran in a process which probably proceeds via a 1,4-dibromo-1,4-dihydro-adduct, indeed such species have been observed at low temperature using H NMR spectroscopy. Reaction with bromine in dimethylfor-mamide at room temperature smoothly produces 2-bromo- or 2,5-dibromofurans. " ... 

A new uranium(VI) silicate, Cs2(U02)(Si206), has been synthesised by a high-temperature, high-pressure hydrothermal method and characterised by single-crystal X-ray diffraction and solid-state NMR spectroscopy. " Reaction of the complex [ CpMo(CO)2 2( t,e(2)P2)] (1) with Cu-I halides leads to the quantitative formation of the novel one-dimensional linear polymers [CuX Cp2Mo2(CO)4)-(p,s(2) s(l)P2) ]n (X-Cl (4). Br (5), I (6)). The solid-state structures are compared and their remarkable influence on the respective P MAS NMR spectra is interpreted with the help of density functional theory (DFT) calculations on model compounds. ... 

In contrast to IR and NMR spectroscopy, the principle of mass spectrometry (MS) is based on decomposition and reactions of organic molecules on theii way from the ion source to the detector. Consequently, structure-MS correlation is basically a matter of relating reactions to the signals in a mass spectrum. The chemical structure information contained in mass spectra is difficult to extract because of the complicated relationships between MS data and chemical structures. The aim of spectra evaluation can be either the identification of a compound or the interpretation of spectral data in order to elucidate the chemical structure [78-80],... 

Because six membered rings are normally less strained than five membered ones pyranose forms are usually present m greater amounts than furanose forms at equilib rium and the concentration of the open chain form is quite small The distribution of carbohydrates among their various hemiacetal forms has been examined by using H and NMR spectroscopy In aqueous solution for example d ribose is found to contain the various a and p furanose and pyranose forms m the amounts shown m Figure 25 5 The concentration of the open chain form at equilibrium is too small to measure directly Nevertheless it occupies a central position m that mterconversions of a and p anomers and furanose and pyranose forms take place by way of the open chain form as an inter mediate As will be seen later certain chemical reactions also proceed by way of the open chain form... 

Measurement of Unsaturation. The presence of double bonds in a fatty acid side chain can be detected chemically or through use of instmmentation. Iodine value (IV) (74) is a measure of extent of the reaction of iodine with double bonds the higher the IV, the more unsaturated the oil. IV may also be calculated from fatty acid composition. The cis—trans configuration of double bonds may be deterrnined by infrared (59) or nmr spectroscopy. Naturally occurring oils have methylene-intermpted double bonds that do not absorb in the uv however, conjugated dienes maybe deterrnined in an appropriate solvent at 233 nm. 

W. A. Nugent and J. M. Mayer, Metal-Eigand Multiple Bonds The Chemistry of Transition Metal Complexes Containing Oxo, Nitrido, Imido, Jilkylidene, orJilkylidyne Eigands,Jolm. Wiley Sons, Inc., New York, 1988. Contains electronic and molecular stmcture, nmr, and ir spectroscopy, reactions, and catalysis. 

The results supported the proposal of Glu-165 as the general base and suggested the novel possibility of neutral histidine acting as an acid, contrary to the expectation that His-95 was protonated [26,58]. The conclusion that the catalytic His-95 is neutral has been confinned by NMR spectroscopy [60]. The selection of neutral imidazole as the general acid catalyst has been discussed in terms of achieving a pX, balance with the weakly acidic intermediate. This avoids the thermodynamic trap that would result from a too stable enediol intermediate, produced by reaction with the more acidic imidazolium [58]. 

NMR spectroscopy is veiy widely used for detection of intermediates in organic reactions. Proton magnetic resonance is most useful because it provides the greatest... 

Again, the chloride is almost exclusively the exo isomer. The distribution of deuterium in the product was determined by NMR spectroscopy. The fact that 1 and 2 are formed in unequal amoimts excludes the symmetrical bridged ion as the only intermediate. The excess of 1 over 2 indicates fliat some syn addition occurs by ion-pair collapse before the bridged ion achieves symmetry with respect to the chloride ion. If the amount of 2 is taken as an indication of the extent of bridged-ion involvement, one would conclude that 82% of the reaction proceeds through this intermediate, which must give equal amoimts of 1 and 2. 

An elegant application of Se NMR spectroscopy, in conjunction with N NMR spectroscopy, involves the detection of the thermally unstable eight-membered rings (RSeN)4 (3.13) from the reactions of a mixture of seleninic anhydrides (RSeO)20 (R=Ph, Pr) and N-enriched... 

It would be pertinent to point out (25,27) that the trisubstituted isomer of the enamine of 2-aIkylcyclohexanone reacts in a quantitative manner with ethyl azodicarboxylate to give the addition product (35). This reaction in Conjunction with NMR spectroscopy can thus be employed for the determination of the amount of the trisubstituted isomer. According to the authors, hydrolysis of 35 furnishes the corresponding cw-2,6-disubstituted cyclohexanone (36) this seems unlikely since it would involve the stereo-electronically unfavored equatorial protonation of the enamine. 

Enamines of several methyl ketones have been prepared and their isomer content estimated by NMR spectroscopy (13,39,43). The reaction of Ti[N(CH3)2l4 as the amine source and 3-methyl-2-butanone gave only 26 (Ri = Rj = CH3), which could be isomerized by prolonged heating to a 1 1 mixture ofthatenamine and enamine 27 (R, = Rj = CH3)(39). The reaction of morpholine and 3-methyl-2-butanone in benzene with a trace of acetic... 

Although the emphasis in this chapter has been on tbe synthesis and mechanism of formation of simple enamines, brief mention will be made of the addition of amines to activated acetylenes to indicate the interest and activity in this area of substituted enamines. Since such additions tend to be stereospecific, inclusion in this section seems apropos. The addition of amines to acetylenes has been much studied 130), but the assigning of the stereochemistry about the newly formed double bond could not be done unequivocally until the techniques of NMR spectroscopy were well developed. In the research efforts described below, NMR spectroscopy was used to determine isomer content and to follow the progress of some of the reactions. 

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