Perspective formulae

Fig. 1. Stmctural representations of sucrose (a) Haworth perspective formula, and (b) conformational stmcture of sucrose in soHd crystals. Adapted from...

To specify enantiomeric configuration, the pre-numbered perspective formula is so oriented in three dimensions that its numbering will proceed from right to left around the front of the ring, as customary for... 

Disaccharides are named by adding the name of a glycosyl group as a prefix to that of the monosaccharide chosen as parent, as exemplified by a-lactose (a Haworth perspective formula and a conformational formula are shown). 

Alkanes have only -hybridized carbons. The conformation of alkanes is discussed in Chapter 3 (see Section 3.2.2). Methane (CH4) is a nonpolar molecule, and has four covalent carbon-hydrogen bonds. In methane, aU four C—H bonds have the same length (1.10 A), and all the bond angles (109.5°) are the same. Therefore, all four covalent bonds in methane are identical. Three different ways to represent a methane molecule are shown here. In a perspective formula, bonds in the plane of the paper are drawn as solid hues, bonds sticking out of the plane of the paper towards you are... 

FIGURE 3-3 Stereoisomerism in n-amino acids, (a) The two stereoisomers of alanine, l- and o-alanine, are nonsuperimposable mirror images of each other (enantiomers), (b, c) Two different conventions for showing the configurations in space of stereoisomers. In perspective formulas (b) the solid wedge-shaped bonds project out of the plane of the paper, the dashed bonds behind it. In projection formulas (c) the horizontal bonds are assumed to project out of the plane of the paper, the vertical bonds behind. However, projection formulas are often used casually and are not always intended to portray a specific stereochemical configuration. 

FIGURE 7-2 Three ways to represent the two stereoisomers of glyc-eraldehyde. The stereoisomers are mirror images of each other. Ball-and-stick models show the actual configuration of molecules. By convention, in Fischer projection formulas, horizontal bonds project out of the plane of the paper, toward the reader vertical bonds project behind the plane of the paper, away from the reader. Recall (see Fig. 1-17) that in perspective formulas, solid wedge-shaped bonds point toward the reader, dashed wedges point away. 

Haworth perspective formulas like those in Figure 7-7 are commonly used to show the stereochem-... 

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. 

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. 

The historical aspects of Emil Fischer s fundamental conventions for writing stereoformulas in a plane have been thoroughly delineated.2 It may be mentioned that the perspective formulas generally attributed to W. N. Haworth were actually a revival of J. Bdeseken s cyclic formulas. ... 

Determine the relationship between the pairs of compounds written as perspective formulas as being enantiomers, diastereomers, conformational isomers, cis-trans... 

Whenever a ring has to be constructed, you should consider the possibility of cycloaddition reactions, especially [4 + 2] cycloaddition by the Diels-Alder reaction. A first glance at 9, written in the usual sawhorse-perspective formula, might lead to overlooking the possibility of constructing the skeleton by [4 + 2] addition, because the compound seems only to be made up of five-membered rings. If the structure is rewritten as 10, the six-membered ring stands out much more clearly ... 

Haworth s perspective formulas, III, 18 Heat of combustion, of sucrose, IV, 16 Helianthate, of streptomycin, III, 345, 346... 

Convert the following perspective formulas to Fischer projections. 

Convert the following Fischer projections to perspective formulas. COOH CHO... 

In Haworth s perspective formula the plane of the pyranose or furanose ring is assumed to be perpendicular to the plane of paper. The substituents are parallel to this plane and project either above or below the plane of the ring (Fig. 2-6). Hydrogen atoms are indicated by a bar or not at all. 

Because the plane of the paper is the plane of reference, the new formulas may be rotated in the plane of the paper without alteration of their significance, although this may not be true of all perspective formulas. ... 

Theory predicts the possibility of the existence of nine stereoisomeric hexahydroxycyclohexanes. No completely satisfactory convention has been devised for depicting these on a plane surface but custom and convenience at the present time justify alteration of the bond angles to depict the inositols by the perspective formulas I to IX. ... 

Haworth perspective formulas. A method for representing cyclic chemical structures (sugars) in order to define the configuration around each chiral center. 

Stereoisomers of glyceraldehyde. (a) Perspective formulas showing tetrahedral arrangement of the chiral carbon 2 with four different substituents, (b) Projection formulas in which the horizontal substituents project forward and the vertical substituents project backward from the plane of the page, (c) A common method of representation. 

FIGURE 1-20 Two types of stereoisomers. There are four different 2,3-disubstituted butanes (n = 2 asymmetric carbons, hence 2" = 4 stereoisomers). Each is shown in a box as a perspective formula and a ball-and-stick model, which has been rotated to allow the reader to... 

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