N.m.r. studies

Thompson has recently obtained clear evidence, from n.m.r. studies of the reaction mixture, that the observed product (vl) is not produced via 1,4-dimethyl-5-nitronaphthalene. 

Katritzky and Topsom have reviewed the information available, largely from infrared and n.m.r. studies, concerning the distortion of the tt-electron system in the benzene ring brought about in the ground state by substituents. Of particular interest is the observation that both n.m.r. studies (of m- F and chemical shifts) and infrared investigations (of the intensities of bands due to certain skeletal vibrations) suggest that the value of Taft s [Pg.226]

Water exchange kinetics in labile aquo and substituted aquo transition metal ions by means of 170 n.m.r. studies. J. P. Hunt, Coord. Chem. Rev., 1971, 7,1-10 (29). 

N.m.r. studies of coordination complexes using lanthanide shift reagents. L. F. Lindov, Coord. 

In this article, a treatment of n.m.r. studies on fluoro sugars is omitted, because fundamental studies in this field had already been described, and... 

By application of first-order, kinetic equations, B. Anderson and Degn claimed that an equilibrated (25°) aqueous solution of D-fructose contains 31.56% of jS-D-fructofuranose and 68.44% of -D-fructopyranose. N.m.r. studies, however, showed that, at equilibrium, a solution of D-fructose contains /3-D-fructopyranose, -D-fructofuranose, a-D-fructofuranose, and a trace of a-D-fructopyranose the distribution of these isomers was shown by gas-liquid chromatography to be 76,19.5, and 4%, respectively. Based on Anderson and Degn s result, Shallenberger reasoned that, as 0.68 X 1.8 = 1.22 (which approximates the reported sweetness of mutarotated D-fructose ), the furanose form(s) must possess very little sweetness. 

B (hydrogen-bond acceptor) unit, as it is also present in many of the derivatives that are not sweet. Its presence in these derivatives promotes the cis orientation of the amide (or thioamide) bond formed with the aniline amino group, as it is known, from infrared and n.m.r. studies, that a bulky substituent on an amide (or thioamide) favors the cis orientation, owing to the steric interaction between the bulky group and the carbonyl oxygen atom. Such an arrangement will bring the AH,B system into the correct spatial separation from the D unit. 

The ynthesis of alkyl(phenyl)trimethylsilylphosphines (59a, b) and the results of an n.m.r. study of their inversion have been reported. The inversion of these compounds has a AG barrier of 19 kcal mol, and a comparison of this value with that of methylphenyl-t-butylphosphine (60), which is known to be about 33 kcal mol at 130 °C, has been made. These data have been discussed in terms of a facilitation of inversion by the react with the dichloro-compounds (61) in which the central atom varies, as shown below. 

Other workers have used the fused ring system (104) and 4,5-dimethyl substitutions (105) to simplify n.m.r. studies by restriction to one chair form. In each case the stable configuration had an axial alkoxy-group at phosphorus. 

N.m.r. studies are reported on the triethylphosphine and trisdi-methylaminophosphine complexes with boron halides, and triethylphos-phine complexes with aluminium chloride. A correlation of Sp with the number of phosphorus ligands in metal carbonyl complexes has led to a qualitative rationalization of 8p in terms of a- and 7r-bonding. ... 

A differential vapour-pressure technique has been used to determine the molecular weights of phosphonic and phosphinic acids in 95% ethanol. Cryoscopic and n.m.r. studies have been made on solutions of phosphinic acids in sulphuric acid and oleum. Mass spectrometry has indicated the ready formation of phosphinylium ions after electron bombardment of phosphonic and phosphinic acids and their derivatives. However, the cryoscopic results in sulphuric acid indicated that reaction did not proceed beyond protonation, and the n.m.r. study on oleum solutions suggested that sulphonation occurred. 

Cruikshank, M. C., Dent Glasser, L. S., Barri, S. A. I. Pollett, J. F. (1986). Penta-co-ordinated aluminium a solid-state Al N.M.R. study. Journal of the Chemical Society, Chemical Communications, 23-40. 

Miscellaneous Reactions of Phosphines.- The role of chiral phosphines as ligands in the catalysis of reactions leading to the formation of chiral products has been reviewed.1111 A procedure for the determination of the enantiomeric excess in chiral phosphines has been developed, based on 13C n.m.r. studies of the diastereoisomeric complexes formed by phosphines with the chiral pinenyl nickel bromide complex. 111 Studies of the sulphonation of triphenylphosphine and of chiral arylphosphines have been reported in attempts to prepare water soluble ligands which aid... 

An n.m.r. study of the permutational isomerisations within a series of amidium fluorophosphates (133) has revealed an irregular mechanism with dissociation of the P-N and also the P-0 bonds of the bidentate ligands and the formation of five-coordinate intermediates (134)61. Reversible intramolecular migrations of pentaco-ordinate phosphorus in the N-C-N triad of amidines (e.g. 135, 136,... 

N.m.r. studies of liquid crystal media showed that phenyl sulphonate counter ions induced abrupt changes in the dipolar coupling of methy1phosphonate. 61... 

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