Acetyl groups, determination

Acetyl Groups Determine the content of acetyl groups in starch acetate, acetylated distarch adipate, and acetylated distarch phosphate as directed under Acetyl Groups, Appendix X. 

A change in other physical properties, such as conve rsion of a liquid unknown to a solid derivative, is anotlau indication of reaction. In special instancf s, t.he reaction product may be isolated, washed free from acids, and the pr(is< nce of tin acetyl group determined by saponification tests (pag(i 140). 

For the determination of the number of acetyl groups in pentacetyl-glucose, see p. 456,... 

The analyses which follow are arranged in the order in which they would be applied to a newly discovered substance, the estimation of the elements present and molecular weight deter-minations(f.e., determination of empirical and molecular formulae respectively) coming first, then the estimation of particular groups in the molecule, and finally the estimation of special classes of organic compounds. It should be noted, however, that this systematic order differs considerably from the order of experimental difficulty of the individual analyses. Consequently many of the later macro-analyses, such as the estimation of hydroxyl groups, acetyl groups, urea, etc. may well be undertaken by elementary students, while the earlier analyses, such as estimation of elements present in the molecule, should be reserved for more senior students. 

I. DETERMINATION OF NUMBER OF ACETYL GROUPS IN TRIACETIN (TRIACETYL-GLYCEROL) C3H6(O COCH3)3. Molecular Weight, 218. 

Because the position of electrophilic attack on an aromatic nng is controlled by the direct ing effects of substituents already present the preparation of disubstituted aromatic com pounds requires that careful thought be given to the order of introduction of the two groups Compare the independent preparations of m bromoacetophenone and p bromoace tophenone from benzene Both syntheses require a Friedel-Crafts acylation step and a bromination step but the major product is determined by the order m which the two steps are carried out When the meta directing acetyl group is introduced first the final product IS m bromoacetophenone... 

The hexahydro derivatives are weakly basic substances, some of them forming hydrochlorides. Dioxohexahydrotriazine yields a 1,5-diacetyl derivative (35), in which the positions of the acetyl groups were determined by acetylation of the A-alkyl derivatives and methylation with diazomethane according to Scheme 4. ... 

Compound 68 can also be obtained by an acid-catalyzed cyclization of 42, which was prepared by the Michael addition reaction of 39 to mesityl oxide as shown in Section IV.A. As for the product 69, the presence of the tosyloxy group at the 5 position instead of the 6 position is determined, utilizing the anisotropy effect of the 1-acetyl group to the C-7 proton, by comparing its H NMR spectrum with that of 70, obtained in 69% yield by the treatment of 69 with NaH and AcCl. 

Rha, Ara and Gal are the neutral sugar components from all the fractions. Xyl is not present in Fla and is significantly present in the hemicellulose fractions, indicating that this monosaccharide is component of hemicellulosic polymers. Chemical composition of the water fractions were determined (Table V). High protein contents and the presence of O-acetyl-groups were observed in four aqueous fractions. Neutral sugar and uronic acid composition points to inclusion of these polymers in the class of pectic polysaccharides. 

AE catalyses the cleavage of acetyl groups from different substrates. The enzyme activity was determined by measuring the release of acetic acid. The amount of acetic acid was measured spectrophotometrically using an acetic acid analysis kit (Boehringer, Mannheim). The activity of AE was measured in 0.6% sugar beet pectin solubilised in 25 mM Na-succinate pH 6.2 and incubated with enzyme fraction in total 500 nl assay. The samples were incubated at 40°C and aliquots were examined after 0, 1, 2 and 3 hours of incubation. The enzyme reaction was stopped by incubating the samples at lOO C for 5 min. Precipitated... 

The rationale for the cyclopent[Z>]indole design discussed above was that the quinone methide would build up in solution and intercalate/alkylate DNA. Enriched 13C-NMR studies indicate that the quinone methide builds up in solution and persists for hours, even under aerobic conditions (Fig. 7.21). In contrast, the quinone methide species formed by known antitumor agents (mitomycin C) are short lived and highly reactive. The spectrum shown in Fig. 7.21 also shows the N to O acyl transfer product that we isolated and identified. However, we could not determine if the quinone methide structure actually has the acetyl group on the N or O centers. 

There is strong cross-reaction between S11A and S18. The partial structures proposed for S18 (Refs. 1 and 38), 17 and 18, with glycerol phosphate and the O-acetyl group linked to positions not yet determined, are also remarkably similar to that of S11A. 

Baddiley and coworkers42 have studied the structure of S13, which is composed of D-galactose, D-glucose, 2-acetamido-2-deoxy-D-glucose, and ribitol residues, and phosphate groups in the molar proportions 2 1 1 1 1. O-Acetyl groups are also present. A neutral pentasaccharide was obtained by hydrolysis with alkali, followed by enzymic dephosphorylation. On mild, acid hydrolysis, this yielded two main products, a trisaccharide (19) and a disaccharide (20), the structures of which were determined by conventional methods. 

Strain and steric properties of the alkenes determine the rate of insertion. The carbomethoxy complex (dppp)PdC(0)OCH3+ turned out to be less reactive than the corresponding acetyl-palladium (dppp)PdC(0)CH3+, which was ascribed to the higher nucleophilicity of the acetyl group as compared to the carbomethoxy group. 

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