Fructose Fischer projections

Fischer projection, monosaccharides acyclic form, 56-57 cyclic forms, 59-60 modified, 60-61 Fluorine chemistry, 18-19 D-Fructofuranosides, degradation, 445 Fructofuranosyl cation, 217 Fructofuranosyl fluorides, 217 Fructose... 

Monosaccharide structures may be depicted in open-chain forms showing their carbonyl character, or in cyclic hemiacetal or hemiketal forms. Alongside the Fischer projections of glucose, ribose, and fructose shown earlier, we included an alternative... 

FIGURE 7-7 Pyranoses and furanoses. The pyranose forms of o-glucose and the furanose forms of o-fructose are shown here as Haworth perspective formulas. The edges of the ring nearest the reader are represented by bold lines. Hydroxyl groups below the plane of the ring in these Haworth perspectives would appear at the right side of a Fischer projection (compare with Fig. 7-6). Pyran and furan are shown for comparison. 

The carbohydrate most likely to appear on the MCAT is fructose or glucose. Both are six carbon carbohydrates called hexoses. These may appear as Fischer projections or ring structures. The Fischer projections are shown below ... 

See the answer to Problem 16.20 for the Fischer projection formula of D-fructose. 

Monosaccharides, or simple sugars, are carbohydrates that cannot be hydrolyzed to simpler compounds. Figure 23-1 shows Fischer projections of the monosaccharides glucose and fructose. Glucose is a polyhydroxyaldehyde, and fructose is a polyhydroxy ketone. Polyhydroxyaldehydes are called aldoses (aid- is for aldehyde and -ose is the suffix for a sugar), and polyhydroxyketones are called ketoses (ket- for ketone, and -ose for sugar). 

The formulas of D-glucose and D-fructose using simplified Fischer projections may also be represented as follows ... 

The Bilik reaction applied to 2-ketoses yield 2-hydroxymethyl aldoses in which the tertiary carbon originates from C2 of the ketose and the C2 hydroxyl is on the opposite side to the C3 hydroxyl of the ketose (in the Fischer projection). Thus, o-fructose yield o-hamamelose. The position of equilibrium, however, lies towards the straight-chain sugar, although it can be pulled over somewhat towards the branched-chain aldose by the addition of borate. The mechanism in Figure 6.9 again explains the main reaction, but not the formation of sorbose as a by-product, which probably arises from a metal ion-promoted hydride shift, as there is no isotope exchange with solvent. The Bilik reaction can be applied to the production of l-deoxy-o-xylulose from 2-C-methyl-D-erythrose the reaction is particularly clean and only the two... 

In D-family sugars, the OH on the chiral carbon farthest from the carbonyl group is on the right side in a Fischer projection formula. So both (+)-glucose and (-)-fructose are D-sugars despite their rotation of plane-polarized light in opposite directions. 

Monosaccharides generally contain multiple chirality centers, and Fischer projections are used to indicate the configuration at each chirality center. Glucose and fructose are two examples of simple sugars. 

Although D-fructose is not an epimer of D-glucose or D-mannose (D-fructose is a ketohex-ose), all three yield the same phenylosazone. (a) Using Fischer projection formulas, write an equation for the reaction of fructose with phenylhydrazine. (b) What information about the stereochenfistry of D-fructose does this experiment yield ... 

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