Fischer Projections of Monosaccharides

We can also draw Fischer projections for the monosaccharides that typically have five or six carbon atoms with several chiral carbons. As discussed in the previous section, the —OH group on the chiral carbon farthest from the carbonyl group is used to determine the D or L stereoisomer. The following are the Fischer projections for the d and l stereoisomers of ribose, a five-carbon monosaccharide, and the d and l stereoisomers of glucose, a six-carbon monosaccharide. 

The vertical carbon chain is numbered starting from the top carbon. In each pair of mirror images, it is important to see that the —OH groups on chiral atoms are reversed so that they appear on the opposite sides of the molecule. For example, in L-ribose, all of the —OH groups are drawn on the left side of the vertical line. In the mirror image, o-ribose, all of the —OH groups are drawn on the right side of the vertical line. 

Chiral atom farthest from the carbonyl group 

Determine if each Fischer projection is chiral or achiral. If chiral, identify it as the D or L stereoisomer and draw the mirror image. 

Does this Fischer projection represent the d or l stereoisomer  

---

Qing-zhi Zhang and Shen-song Zhang, "A New Method to Convert the Fischer Projection of Monosaccharide to the Haworth Projection," J. Chem. Educ., Vol. 76, 1999, 799-801. 

Carbohydrates Chiral Molecules Fischer Projections of Monosaccharides Haworth Structures of Monosaccharides Chemical Properties of Monosaccharides Disaccharides Polysaccharides... 

Fischer Projections of Monosaccharides LEARNING GOAL Use Fischer projections to draw the Don stereoisomers for glucose, galactose, and fmctose. 

Thomson JOV Click Organic Interactive to learn to draw and interpret Fischer projections of simple monosaccharides. 

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... 

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). 

Although Fischer projections are commonly used to depict monosaccharides with many stereogenic centers, care must be exercised in using them since they do not give a true picture of the three-dimensional structures they represent. Because each stereogenic center is drawn in the less stable eclipsed conformation, the Fischer projection of glucose really represents the molecule in a cylindrical conformation, as shown in Figure 27.2. 

Monosaccharides and other sugars will often be represented in this book by Fischer projections (Figure 11.1). Recall that, in a Fischer projection of a molecule, atoms joined to an asymmetric carbon atom by horizontal bonds are in front of the plane of the page, and those joined by vertical bonds arc behind the page (see the Appendix in Chapter 1). Fischer projections provide clear and simple views of the stereochemistry at each carbon center. 

You would do well to remember the configuration of groups on the Haworth projection of both a-D-glucopyranose and jS-D-glucopyranose as reference structures. Knowing how the Fischer projection of any other monosaccharide differs from that of D-glucose, you can then construct the Haworth projection of that other monosaccharide by reference to the Haworth projection of D-glucose. 

In a Fischer projection of a monosaccharide, the carbon chain is written vertically, with the most highly oxidized carbon toward the top. Horizontal lines show groups projecting above the plane of the page and vertical lines show groups projecting behind the plane of the page. 

Carbohydrates are polyhydroxy aldehydes and ketones that are commonly known as sugars. A monosaccharide is a carbohydrate composed of one sugar unit and a disaccharide is a carbohydrate composed of two monosaccharide units. An oligosaccharide is composed of 2-10 monosaccharide units a polysaccharide is composed of 10 or more monosaccharide units. An aldose is a carbohydrate that contains an aldehyde unit and a ketose is a carbohydrate that contains a ketone unit. Monosaccharides are categorized by the total number of carbons in the structure triose, tetrose, pentose, hexose, etc. The d and 1 configurations of a monosaccharide are based on the Fischer projection of d-glyceraldehyde. A Fischer projection is an older representation of sugars. 

A description of the pioneering work of Emil Fischer in the period around 1890, especially relating to his elucidation of the molecular configuration of glucose and aspects of his philosophical view of chemistry, has appeared. Lemieux and Spohr have looked in detail at how Fischer was led to the "lock and key" concept for enzyme specificity. An animated 386-based PC program with VGA graphics has been produced to assist visualization of the relationship between Fischer and Haworth projections of monosaccharides. ... 

A Fischer projection of a monosaccharide is used to show its structure and thus keep track of stereochemistry. 

In a Fischer projection, the monosaccharide is drawn in the open-chain form and the carbonyl carbon atom is placed at the top of the structure. Horizontal lines represent groups projecting above the plane of the paper, and vertical lines represent groups projecting below the plane of the paper. 

Fischer projections and, 977-978 glycosides and, 989-990 l- 4 links in, 997-998 origin of name. 973 photosynthesis of, 973-974 see also Aldose, Monosaccharide vaccines from, 1004-1005 Carbon, ground-state electron configuration of, 6... 

Monosaccharides generally contain several chiral carbons and therefore exist in a variety of stereochemical forms, which may be represented on paper as Fischer projections. Epimers are sugars that differ in configuration at only one carbon atom. 

---