NMR spectroscopy multinuclear

Raman and multinuclear NMR spectroscopy have been used to study the reaction product of pentafluoropyridine with XeF+AsF6 in anhydrous HF. Identified in the mixture was a fluoro(pentafluoropyridine)xenon(II) cation with the Xe bonded to the ring N (88CC257). 

The acid-base interaction in group 13-stibine and -bismuthine adducts seems to be very weak as is indicated by mass spectroscopic studies, which never showed the molecular ion peak but only the respective Lewis acid and Lewis base fragments. The extreme lability in the gas phase may also account for the fact that there are only very few reports on thermodynamic data of group 13-stibine or bismuthine adducts in the literature. Therefore, multinuclear NMR spectroscopy and single crystal X-ray diffraction are the most important analytical tools for the characterization of such adducts. 

The structures of doubly bonded compounds containing tin readily lend themselves to study by multinuclear NMR spectroscopy, as tin has two NMR active isotopes ll7Sn and ll9Sn. The chemical shifts of doubly bonded tin species in the 119Sn NMR spectrum cover a broad range from 6 = -150 to +835 (Table VI) however, the majority of the signals occur at low field S = 400 or above. 

Reaction of [Ircp Cl2]2 with AgBF4 and (SPPh2)3CH in CH2C12 or Me2CO to which Et3N is added yields [Ircp ( 73-(SPPh2)3C]BF4, which has been structurally characterized.271 The Irm complexes [Ircp L3](PF6)2 (L3 = MeC(CFl2ER)3, E = Se, R = Me E = Te, R = Me, Ph) have been prepared and characterized by IR and multinuclear NMR spectroscopy.647... 

Zinc boryloxides with a tetrameric Zn404 core (45) have only recently been characterized. The single-crystal X-ray structure and multinuclear NMR spectroscopy studies were used as a basis for discussion of deformation of the central core.435 Alkali metal zinc orthoborates MZn4(B03)3 (M = K, Rb, Cs) have been synthesized and single-crystal X-ray structures determined for M = K and Rb.436... 

Routine identification and analytical characterization of all types of NHPs was preferably carried out by multinuclear NMR spectroscopy. Of particularly high diagnostic value are 31P NMR spectra where rather specific chemical shift ranges for heterocycles with different types of P-substituents can be observed. The largest chemical shifts occur for anionic and neutral 1,3,2-diazaphospholes (220-300 ppm) and 1,3,2-diazaphospholenium cations (210-200 ppm). Chemical shifts of P-halogen-l,3,2-diazaphospholenes vary over an overall range of 200-110 ppm and decrease in the order I (205-190 ppm)>Br (194-185 ppm two compounds... 

It is commonly accepted5,6,19 that unstable betaines IV (X = C) are intermediates of the cyclopropanation of olefins with the polar C=C bond by phosphorus ylides. However, only one compound of this type, viz., Me3P( + )-CH2-CMe2-C5H4( ) (1), synthesized in the reaction of dimethyl-fulvene with methylenetrimethylphosphorane, was isolated and characterized by multinuclear NMR spectroscopy.20... 

The first silicon-organophosphorus betaine with a thiolate center (15a) was synthesized by the reaction of stable silanethione (14) with trimethyl-methylenephosphorane (Scheme 8) and characterized by multinuclear NMR spectroscopy.14 Compound 15a is formed under kinetic control and is transformed, under the thermodynamically controlled conditions, into the silaacenaphthene salt (16). The processes presented in this scheme reflect the competition of the basicity and nucleophilicity of phosphorus ylides. Betaine 15b prepared from less nucleophilic and less basic ylide with phenyl substituents at the phosphorus atom is much less resistant toward retro-decomposition compared to the alkyl analog. Its equilibrium concentration does not exceed 6%. 

Multinuclear NMR spectroscopy is a very informative and reliable method for the identification and study of betaines of types I and II in solutions. The main NMR parameters of these compounds are presented in Table IV. The data for some of their carbon analogs 17 are presented for comparison. 

In solution, multinuclear NMR spectroscopy is by far the most informative technique for analyzing the structure and bonding of phosphinocar-benes. In fact, prior to the synthesis and single crystal X-ray analysis of the (phosphino)(phosphonio)carbene 2d,28 the only spectroscopic evidence for the formation of carbenes came from NMR. 

In order to allow for a closer approach of the boron centers, the introduction of flat cyclic boryl moieties with reduced steric hindrance has also been pursued. Thus, the reaction of 26 with 9-chloro-9-borafluorene and 5-bromo-10,l 1-di-hydrodibenzo[b,f]borepin resulted in the formation of diboranes 31 and 32 which bear two different boryl moieties at the pen-positions of naphthalene (Scheme 13). " These diboranes have been characterized by multinuclear NMR spectroscopy and X-ray single-crystal analysis. In 31, the boron center of the borafluorenyl moiety is 7i-coordinated by the zp o-carbon of a mesityl group with which it forms a contact of 2.730(3) A (Fig. 8). As a result of this interaction, the boron center involved in this contact is slightly pyramidalized (Xangie = 355.7°). In the case of 32 (Fig. 9), the distance between the boron center of the boracylic moiety and the zpio-carbon of... 

Multinuclear NMR spectroscopy is being used increasingly to study catalytic reactions. In order for such studies to be possible, all contact betv een the sample solutions and the metal part of the cell body has to be avoided because of possible catalytic effects. All materials in contact vith the sample solution have to be chemically inert and nonmetallic quartz, glass, PTFE, Vespel (polyimide polymer, Dupont de Nemours), PCTFE (poly-chlorotrifluoroethylene), Viton seals, etc. 

The stereochemical course of the reaction catalyzed by dihydroneopterin aldolase has been established <2002JBC28841>. By carrying out the reaction in deuterium oxide and using multinuclear NMR spectroscopy of folate derived from the reaction product, 6-hydroxymethylpterin, it was shown that the late-stage enol intermediate undergoes protonation to form 6-hydroxymethylpterin with deuterium predominantly in the A-configuration. 

Knorr cyclization of a range of iV-susbtituted butyramides in triflic acid yields 4-methyl-17/-quinolin-2-one derivatives704 [Eq. (5.257)]. Suggested intermediates of the transformation directly observed by low-temperature multinuclear NMR spectroscopy (HSO3F SbF5 S02C1E, 40°C) are distonic superelectrophiles formed by diprotonation of the two carbonyl oxygen atoms. 

Scheme 3).11 Compound 2 was isolated in 93% yield by sublimation and characterized by elemental analysis, IR, and multinuclear NMR spectroscopy. Its head-to-tail dimeric structure was unambiguously established by X-ray diffraction analysis (see Section III). 

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