Tollen structure

Two structures were proposed, the Cholley structure and the Tollens structure ... 

D-Mannose reacts with acetone to give a diisopropylidene derivative (Problem 25.61) that is still reducing toward Tollens reagent. Propose a likely structure tor this derivative. 

Thymine, electrostatic potential map of, 1104 structure of, 1101 Thyroxine, biosynthesis of, 551 structure of. 1020 TIme-of-flight (TOP) mass spectrometry, 417-418 Titration curve, alanine, 1023 TMS, see Tetramethylsilane see Trimethylsilyl ether Tollens reagent, 701 Tollens test, 992... 

Problem 15.53 Compound (A), C HgCI, is hydrolyzed to compound (B), C4HgO, which gives an oxime and a negative Tollens test. What is the structure of (A) <... 

Problem 15.55 A compound (C,HgOj) is reduced to pentane. With HjNOH it forms a dioxime and also gives positive iodoform and Tollens tests. Deduce its structure. 4... 

It was first obtained by Hertz [67] who proposed its use as an explosive, since (in the authors opinion) it develops greater explosive strength that PETN but is less sensitive. Tollens and Apel [68] have prepared the initial alcohol (m.p. 156°C) resulting from the reaction of acetone with formaldehyde in the presence of calcium hydroxide, to which they attributed the structure of an enneaheptitol anhydride without, however, determining which hydroxyl groups were dehydrated. 

He favored the currently accepted, cyclic hemiacetal structure for the glucosides, but formulated them with the furanoid ring for glucose proposed in 1883 by B. Tollens. W. N. Haworth later established that the glucose residue in such glucosides is present in the form of a pyranoid ring. 

At a considerably later date. Frankland prepared ethyl methacrylate and methacrylic acid from ethyl a-hydroxyisobutyrate and phosphorus trichloride. Tollen prepared aciylate esters from 2,3-dibromopropionate esters and zinc. Otto Rohm, in 1901. described the structures of the liquid condensation products (including dimers and timers) obtained from the action of sodium alkoxides on methyl and ethyl acrylate. Shortly after World War 1, Rohm introduced a new acrylate synthesis, noting that an acrylate is formed in good yield from heating ethylene cyanohydrin and sulfuric acid and alcohol. A major incentive for the development of a clear, tough plastic acrylate was for use in the manufacture of safety glass. 

The other carbohydrates in cane juice are the soluble polysaccharides vaguely classified under the terms "hemi-celluloses, soluble gums and pectins. It is possible that some of these polysaccharides may enter the juice during the milling of the cane as the plant cell structure is destroyed. A gummy product has been isolated from cane fiber by alkali extraction followed by alcohol precipitation. Acid hydrolysis of this substance yielded crystalline D-xylose and L-arabinose.10 Such gums in Trinidad cane juices were isolated by alcohol precipitation at suitable hydrogen ion concentration and assayed for pentose content by the Tollens 2-fural-dehyde assay the results showed an apparent pentosan content of 0.04-0.07%u of the Brix solids. 

The aldehyde or ketone group of monosaccharides can undergo an intramolecular reaction with one of its own hydroxyl groups to form a cyclic, hemiacetal or hemiketal structure, respectively (Fig. 20). In aqueous solutions, this cyclic structure actually predominates. The open-chain aldehyde or ketone form of monosaccharides is in equilibrium with the cyclic form, but the open structure exists less than 0.5% of the time in aqueous environments. It is the open form that reduces Fehling s or Tollen s... 

The molecular formula, C4H10O, tells us that compound A is saturated. The fact that A can be oxidized with PCC to an aldehyde (note that B gives a positive Tollens test) tells us that A is a primary alcohol. We can draw only two structures for A that are consistent with these data ... 

Given the structure of a sugar, write equations for its reaction with each of the following reagents acetic anhydride, bromine water, nitric acid, sodium borohydride, and Tollens or Fehling s reagent. 

The chemical properties of monosaccharides are further complicated by the fact that they can exhibit tautomerism in aqueous basic solutions (Figure 1.15). This means that after a short time a basic aqueous solution of a monosaccharide will also contain a mixture of monosaccharides that will exhibit their characteristic chemical properties. For example, a solution of fructose will produce a silver mirror when treated with an ammoniacal solution of silver nitrate (Tol-len s reagent). This is because under basic conditions fructose undergoes tautomerism to glucose, whose structure contains an aldehyde group, which reduces Tollen s reagent to metallic silver. 

An unknown carbohydrate of formula C12H22O11 reacts with Tollens reagent to form a silver mirror. An a-glycosidase has no effect on the carbohydrate, but a /3-galactosidasc hydrolyzes it to D-galactose and D-mannose. When the carbohydrate is methylated (using methyl iodide and silver oxide) and then hydrolyzed with dilute HC1, the products are 2,3,4,6-tetra-O-methylgalactose and 2,3,4-tri-(9-methylmannose. Propose a structure for this unknown carbohydrate. 

A test for reducing sugars, employing the same silver-ammonia complex used as a test for aldehydes. A positive test gives a silver precipitate, often in the form of a silver mirror. Tollens reagent is basic, and it promotes enediol rearrangements that interconvert ketoses and aldoses. Therefore, both aldoses and ketoses give positive Tollens tests if they are in their hemiacetal forms, in equilibrium with open-chain carbonyl structures, (p. 1118)... 

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