Hydroxyl groups monosaccharide structure

We will examine the products that would result from cleaving of all the possible combinations of bonds in a monosaccharide. We will do so by considering various subunits of the structme. However, all the subunits react, so we must analyze all carbon-carbon bonds and the attached functional groups to determine the products that can form. First, consider the subunit that contains a primary hydroxyl group. This structural feature exists at the highest numbered carbon atom of an aldose. The unit also occurs at C-1 and the highest numbered carbon atom of a ketose. 

FIGURE 7.21 Amylose and amylopectin are the two forms of starch. Note that the linear linkages are o (1 4), but the branches in amylopectin are o (1 6). Branches in polysaccharides can involve any of the hydroxyl groups on the monosaccharide components. Amylopectin is a highly branched structure, with branches occurring every 12 to 30 residues. 

Monosaccharides can differ in their formulas, their ring sizes, and the spatial orientations of their hydroxyl groups. To analyze the differences between two monosaccharides, begin with structural drawings of the molecules, oriented so the ether linkages are in comparable positions. Then examine the stmctures to locate differences in constituents and bond orientations. 

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 (Figure 1.26). 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 percent of the time in aqueous environments. It is the... 

Chitin is a polysaccharide structurally and functionally related to cellulose. The structure is derived from that of cellulose by replacing one of the hydroxyl groups on each monosaccharide unit by an acetamido group, —NHCOCH3. Chitin is the structural polysaccharide of lower plants, such as fungi, and of invertebrates, particularly arthropods. It is the second most abundant organic substance on Earth. 

With monosaccharides, the structures of the relatively rigid pyranoses and methylpyranosides in the crystalline state can be accurately pr icted if the hydroxyl groups are oriented as in the crystal, in the directions appropriate to form... 

The structures of two (p-bromophenyl)hydrazones have been determined from projection data. The first was that of D-ribose,112 in which the D-ribose is acyclic, in a sickle18 conformation, and C-l, C-2, C-3, and C-4 are coplanar. Rotation of C-5 out of this plane relieves the 0-2, 0-4 interaction that would be present in the extended conformation and brings 0-5 close to 0-2, so that an intramolecular hydrogen-bond can be formed this is the first (and, thus far, the only) case of an intramolecular hydrogen bond in a crystal of a monosaccharide derivative. The hydroxyl groups on C-2, C-3, and C-4 form three intermolecular hydrogen-bonds. 

In monosaccharides where structures differ at C-1 and C-2, hut are the same in the rest of the molecule, we get the same phenylosazone. If we examine the structures of glucose and mannose, the only structural difference we can identify is the orientation of the hydroxyl group at C-2. The rest of the molecules are exactly the same. Therefore, glucose and mannose produce the same phenylosazone. Phenylosazones are highly crystalline solids with characteristic shaped crystals. Shapes are diagnostic of phenylosazone type. 

Monosaccharides commonly form internal hemiacetals or hemiketals, in which the aldehyde or ketone group joins with a hydroxyl group of the same molecule, creating a cyclic structure this can be represented as a Haworth perspective formula. The carbon atom originally found in the aldehyde or ketone group (the anomeric carbon) can assume either of two configurations, a and /3, which are interconvertible by mutarotation. In the linear form, which is in equilibrium with the cyclized forms, the anomeric carbon is easily oxidized. 

V plants through photosynthesis. The term carbohydrate is derived from the fact that plants make these molecules from carbon (from atmospheric carbon dioxide) and water. The term saccharide is a synonym for carbohydrate, and a monosaccharide ( one saccharide ) is the fundamental carbohydrate unit. In most monosaccharides, each carbon atom is bonded to at least one oxygen atom, most often in the form of a hydroxyl group. There are many kinds of monosaccharides. The structures of the two most common ones, glucose and fructose, are shown in Figure 13.2. 

---