Phosphoric esters spectroscopy

The a-furanose (0.6%) and p-furanose (0.3%) forms of o-mannose and the P-furanose form (0.14%) of D-glucose have been detected in aqueous solutions by taking advantage of the high resolving power of n.m.r. spectroscopy. The tautomeric forms adopted by ketoses and their biologically important phosphoric esters at equilibrium have also been discussed. The proportion of carbonyl form present in the equilibrium mixture of each of 23 aldoses and 10 ketoses has been estimated from the c.d. spectrum obtained with a highly sensitive circular dichro-meter. An attempt to calculate the probable specific rotations of a- and P-d-fructofuranose is mentioned in Chapter 21. ... 

Fig. 5.13. GC-ICP-MS P -selective chromatogram of phosphorous esters, equal volumes of each compound ii jected. Note similar response for P in the three compounds. Reproduced from Appl. Spectrosc. [60] with permission of Society for Applied Spectroscopy.

Reactions of Phosphoric Acids and Their Derivatives. - Numerous investigations of phosphate ester hydrolysis continue to be reported. The hydrolysis between 1.5 < pH < 4 of five- and six-membered cyclic phosphoramides (71) has been followed by UV and NMR spectroscopy. Small differences in hydrolysis reactivity for n = 5 and n = 6 constitutes evidence for syn lone pair catalysis. The product ratios from the hydrolysis shows that in the five-membered rings the main product is the one produced by endocyclic cleavage meanwhile, in the six- membered cyclic phosphoramide the kinetic product is the one produced by exocyclic cleavage. The syn orientation of two electron pairs on nitrogen stabilizes the transition state of water approach to the phosphoramides by ca. 3 kcal/moN when compared to the orthogonal attack. (Scheme 12). ... 

Acylation of 3,5-diamino-1,2,4-thiadiazole by ethyl chloroformate yields the 3,5-bis(ethoxycarbonylamino) derivative.67 Phosphorochloridic esters [(RO)2POCl] attack the 3-position preferentially, producing the phosphor-amidic esters (509).390 The action of diphenylphosphinothioic chloride (Ph2PSCl) (see Section IV,C) on Hector s base in pyridine yields a monoacyl derivative, substitution occurring probably at the exocyclic imino group.391 Methylation of 3,5-bisanilino-l,2,4-thiadiazole with sodium hydride-methyl iodide in dimethylformamide produces the mono and dimethyl derivatives, of structures 510 and 511, as shown by 15N and 13C NMR spectroscopy.31... 

So far, no crystallographic evidence for adducts of silanes with aldehydes, ketones, esters, or acyl halides has been reported [81]. Dimethylformamide [86-88] and tetramethylurea [89], however, are known to enter the silicon coordination sphere (e.g., in 13 and 14, respectively). In a similar manner amine-M-oxides (e.g., in 15) [90], phosphine oxides (e.g., in 16 and 17) [90,91], and phosphoric amides [92-94] form hypercoordinated Si complexes. Although dimethyl sulfoxide (DMSO) increases the silicon coordination number (as shown Si NMR spectroscopy) [49], crystallographic evidence for a siUcmi complex with DMSO Ugand(s) is still lacking [81]. 

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