Three-dimensional formulas

Three-dimensional formulas using wedge-dashed wedge-line... 

Fischer projections provide a fnrther approach to the two-dimensional representations of three-dimensional formulae. They become particularly useful for molecules that contain several chiral centres, and are most frequently encountered in discussions of sugars (see... 

Just as it was stated above that two compounds may have the same molecular formula and yet have quite different structural formulas and properties, so there are also many instances in chemistry of compounds which have the same planar structural formula and yet differ in properties. In such cases their differences iri structure can be shown only by three-dimensional formulas or their projections which portray differences In the arrangement in space of the atoms or radicals that make up the molecules of the two compounds. 

A spatial or three-dimensional formula for nitrogen, analogous to the carbon tetrahedron, is not possible because there is no symmetrical solid figure with five corners. Hence it was assumed that certain valencies of the nitrogen atom are directed in special directions. Thus were obtained J. H. van t Hoff s cubic or tetrahedral formula, C. Willgerodt s double tetrahedron, C. A. Bischoff s square pyramid, and the modifications suggested by W. Vaubel, and A. von Baeyer. The tetrahedral and the pyramidal or square formula can be graphically symbolized . ... 

When the three-dimensional formula is viewed from a perspective in which the lowest ranked substituent is away from us, we see... 

Draw the three-dimensional formula of a molecule with a particular configuration, R or S. 

While these experiments stimulated other research, it is sad to relate that the proposed explanation is not correct. It required almost seventy years, however, before it was realized that the curare-like action of the onium salts was a result of their ionic character. Other examples of the role of spatial arrangement were discovered. For example, quoting Stewart Ishizuka (1897) found that maleic acid was a much stronger poison than its stereoisomer, fumaric acid 1.94 grammes for every kilogramme in a dog s weight was a fatal dose of the former acid, while the same dose of fumaric acid was harmless. Similarly these isomers were found to have differential effects on microorganisms. Stewart also rationalized the mydriatic action of tropine and the inactivity of pseudotropine in terms of three-dimensional formulae as shown below (1 and 2). In many ways, these structural representations are close to the present-day conformational structures (pseudotropine = 3, tropine = 4) ... 

As is well known, formaldehyde and ammonia combine to yield hexamethylenetetramine, C0HiaN4. Duden and Scharff7 found that most of the reactions of this substance could be explained on the basis of the three dimensional formula. 

Using models and then drawing three-dimensional formulas, account for this. Label the chiral center in each compound. 

Fig. (15). Selected three-dimensional formulae of spiro compounds.

Fig. (17). Three-dimensional formulae of lactam derivatives and their tetrahedric intermediates.

We shall ordinarily write methane with a dash to represent each pair of electrons shared by carbon and hydrogen (I). To focus our attention on individual electrons, we may sometimes indicate a pair of electrons by a pair of dots (II). Finally, when we wish to represent the actual shape of the molecule, we shall use a simple three-dimensional formula like III or IV. 

In three-dimensional formulas of this kind, a solid wedge represents a bond coming toward us out of the plane of the paper a broken wedge, a bond going away from us behind the plane of the paper and an ordinary line, a bond lying in the plane of the paper. Thus formulas III and IV represent methane as in Fig. 2.2c and Fig. 2.2b, respectively. 

In the long-chain molecule any of the N chain-elements is equivalent to a step in three-dimensional space, the direction of which is entirely arbitrary. The three-dimensional formula differs but slightly from the formula (5), and may be expressed... 

Last, when drawing three-dimensional formulas for molecules ... 

Some examples of three-dimensional formulas are shown below. 

Using a three-dimensional formula, show the direction of the dipole moment of CH3OH. PRACTICE PROBLEM 2.6 Write 8-1- and 8— signs next to the appropriate atoms. 

Write a three-dimensional formula for each of the following molecules using the wedge-dashed wedge-line formalism. If the molecule has a net dipole moment, indicate its direction with an arrow, -i- . If the molecule has no net dipole moment, you should so state. 

When we do conformational analysis, we will find that certain types of structural formulas are especially convenient to use. One of these types is called a Newman projection formula and another type is a sawhorse formula. Sawhorse formulas are much like dash-wedge three-dimensional formulas we have used so far. In conformational analyses, we will make... 

Interchanging two groups of a model or three-dimensional formula Is a useful test for determining whether structures of two chiral molecules are the same or different. 

An example of a molecule of this type is 2-propanol carbon atoms 1 and 3 bear three identical hydrogen atoms and the central atom bears two identical methyl groups. If we write three-dimensional formulas for 2-propanol, we find (Fig. 5.6) that one structure can be superposed on its mirror image. 

Some of the molecules listed here have a chirality center some do not. Write three-dimensional formulas for both enantiomers of those molecules that do have a chirality center. 

PRACTICE PROBLEM 5.8 Write three-dimensional formulas and designate a plane of symmetry for all of the... 

PRACTICE PROBLEM 5.16 Write three-dimensional formulas for the (5) isomers of (a) methyldopa, (b) penicillamine, and (c) ibuprofen. 

Write three-dimensional formulas for all of the stereoisomers of each of the following PRACTICE PROBLEM 5.22 compounds. Label pairs of enantiomers and label meso compounds. 

Chloramphenicol (at right) is a potent antibiotic, isolated from Streptomyces venezuelae, that is particularly effective against typhoid fever. It was the first naturally occurring substance shown to contain a nitro (— NO2) group attached to an aromatic ring. Both chirality centers in chloramphenicol are known to have the (/ ) configuration. Identify the two chirality centers and write a three-dimensional formula for chloramphenicol. 

Let us consider how we would relate a three-dimensional formula for 2,3-dibromobutane using solid and dashed wedges to the corresponding Fischer projection formula. 

PRACTICE PROBLEM 5.31 Write bond-line three-dimensional formulas for the starting compound, the product,... 

Albuterol, shown here, is a commonly prescribed asthma medication. For either enantiomer of albuterol, draw a three-dimensional formula using dashes and wedges for bonds that are not in the plane of the paper. Choose a perspective that allows as many carbon atoms as possible to be in the plane of the paper, and show all unshared electron pairs and hydrogen atoms (except those on the methyl groups labeled Me). Specify the R,S) configuration of the enantiomer you drew. 

There are four dimethylcyclopropane isomers, (a) Write three-dimensional formulas for these isomers, (b) Which of the isomers are chiral (c) If a mixture consisting of 1 mol of each of these isomers were subjected to simple gas chromatography (an analytical method that can separate compounds according to boiling point), how many fractions would be obtained and which compounds would each fraction contain (d) How many of these fractions would be optically active ... 

Write three-dimensional formulas for and give names using (R)— S) and (E)—(Z) designations for the isomers of ... 

Explain using mechanistic arguments involving Newman projections or other three-dimensional formulas why the reaction of 2-bromo-l,2-diphenylpropane (either enantiomer) with sodium ethoxide (EtONa) in ethanol (EtOH) at 80 °C produces mainly ( )-l,2-diphenylpropene [little of the (Z) diastereomer is formed]. 

Write a three-dimensional formula for the product formed when 1-methylcyclohexene is treated with each of the following reagents. In each case, designate the location of deuterium or tritium atoms. 

PRACTICE PROBLEM 22.2 Write three-dimensional formulas for each aldotetrose and ketopentose isomer in... 

Consider the formula for (i )-lactic acid, to the left of the mirror in Figure 5.10. If we project that three-dimensional formula onto a plane, as illustrated in Figure 5.11, we obtain the flattened Fischer projection formula. 

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