Yield analysis derivation

Formyl-2-methylfuran was converted in 75% yield into derivative 319 by electrolytic methoxylation. A corresponding mixture of cis-diols (320) was treated with Dowex W-50 ion-exchange resin in methanol for four days, to afford 5-deoxy-3-C-(dimethoxymethyl)-DL-eryf/rro-4-pentulose dimethyl acetal (321). Reduction of this compound with lithium aluminum hydride or sodium borohydride gave a mixture of 5-deoxy-3-C-(dimethoxymethyl)pentoses, which was separated by column chromatography on silica gel, to give206 DL-streptose tetramethyl acetal (322) and the isomeric 5-deoxy-3-C-(dimethoxy-methyl)-DL-ribose dimethyl acetal 323 (hjxo ribo = 13 7). Detailed, combined gas-liquid chromatographic-mass spectrometric analysis of the compounds related to streptose (in the form of their trimethyl-silyl derivatives) has been described.207... 

From the product analysis, the following primary quantum yields arc derived (282) ... 

Here we are solely concerned with the light petroleum solubles (designated Fraction A), derived from a xylose/glycine model system. Fraction A was obtained as a yellow solid in 0.05 yield. Analysis by HPLC at 450 nm showed it to consist of at least 25 components (Figure 1), and examination at 315 and 260 nm further increased the number detected. 

Figure 5 Plot of pertrifluoroacetic acid oxidation aliphatic proton yield data derived from P.M.R. and elemental analysis.

In quantitative analysis derivative recording yields an improved detectability of curve data. Comparison of Fig. 6 with its derivative Fig. 13 shows that peak 5 contains another substance in addition to chrysophanol. Derivatives cannot increase the content of information but they may help to identify the total available information especially in overlapping peaks. 

Another intriguing sugar-based metabolite from a cyanobacterium is cyclodextrin 33, isolated from a Hawaiian Tolypothrix byssoidea strain. A range of related metabolites were produced these proved inseparable and were analyzed as a mixture. However, acetylation of the mixture yielded peracetate derivatives that could be separated by HPLC and analysis of both the purified peracetate and the unmodified mixture was used in the elucidation of the major component 33. MS and extensive NMR analysis led to the structure shown. 2D NMR analysis was crucial in the determination of the individual sugar units, while their sequence was solved by difference nuclear overhauser effect (NOE) experiments. The configurations of all sugar units were presumed to be D on the basis of comparison with related cyclodextrins. The Tolypothrix cyclodextrins were found to block the activity of some of the other toxic metabolites produced by this cyanobacterium. " ... 

The rate of chemical conversion of the sample compounds determines the duration of analysis it is also highly desirable that the yield of derivatives should be close to 100%. When elaborating the technique one should therefore make sure that the reaction pro-... 

The hydrolysis-methylation products are then pyrolysed and the pyrolysis products examined by gas chromatography to provide knowledge on polymer structure. This technique has been applied in hydrolysis - methylation - Py-GC to polycarbonates and phenolics. Polycarbonate main chains degraded quantitatively at the carbonate linkages to yield dimethyl derivatives of breakdown products such as bisphenol A. Such studies provided information on polymer structure including end-group analysis. 

Our attempts to obtain a crystalline oxazolidinone were eventually successful with the (L)-iV-i-butoxycarbonyl derivatives and 4 -biphenylcarboxaldehyde, leading to 29d,[26] In solution, flie typical 85 15 equilibrium ratio of cis and trans diastereomers is observed (Table I, entry 4), When the solvent was partially removed and the residue suspended in teft-butyl methyl ether, an off-white solid precipitated, which consists of pure cw-29d in 88% yield. Analysis of the mother liquors shows very minor amounts of cis and trans product in a 85 15 ratio, along with some unreacted carbamate and a,a-dichloro biphenyl. The presence of both cis and trans isomers in the mother liquor is clear evidence that a crystallization-induced asymmetric transformation is responsible for the high selectivity. 

Thermal gravimetric analysis was performed on a Cahn 121 electrobalance from 25-800 C at a rate of 10 C/min with data collection every two seconds, under a nitrogen atmosphere Cahn software allowed processing of the data to yield first-derivative thermograms. 

Using a guided ion beam instrument the translational energy dependent reaction cross sections of endothemiic fragmentation processes can be detemiined [32]. Modelling these cross sections ultimately yields their energy tln-esholds and a great deal of valuable themiochemical infomiation has been derived with this teclmique. Precision of 0.2 eV can be obtained for reaction tln-esholds. Bimolecular reactions can also be studied and reaction enthalpies derived from the analysis of the cross section data. 

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