Bromochlorofluoromethane

Bromochlorofluoromethane IS a known compound and samples selectively enriched in each enantiomer have been described in the chemi cal literature In 1989 two chemists at Polytechnic Uni versity (Brooklyn New York) described a method for the preparation of BrClFCH that IS predominantly one enantiomer... 

In organic chemistry chirality most often occurs m molecules that contain a car bon that is attached to four different groups An example is bromochlorofluoromethane (BrClFCH)... 

As shown in Figure 7 1 the two mirror images of bromochlorofluoromethane cannot be superimposed on each other Because the two mirror images of bromochlorofluoro methane are not supenmposable BrClFCH is chiral... 

Verify that dibromochloromethane is achiral by superimposing models of its two mirror image forms In the same way venfy that bromochlorofluoromethane is chiral... 

CFlBrClF (bromochlorofluoromethane) dipole moment, 99ff enantiomers, 79 symmetry elements, 79ff CF12F2 (difluoromethane) cartesian axes, 89 symmetry elements, 77, 83 CF13F (methyl fluoride) dipole moment, 116 symmetry elements, 74, 83 C Fl3F (methyl fluoride) vibration-rotation band, 178... 

The minor images of bromochlorofluoromethane have the sane constitution. That is, the atoms are connected in the sane order. But they differ in the anangement of then-atoms in space they are stereoisomers. Stereoisomers that are related as an object and its nonsuperimposable minor image are classified as enantiomers. The word enantiomer describes a paiticulai- relationship between two objects. One cannot look at a single molecule in isolation and ask if it is an enantiomer any more than one can look at an individual human being and ask, Is that person a cousin Fuithennore, just as an object has one, and only one, minor image, a chiral molecule can have one, and only one, enantiomer. 

Let s return to bromochlorofluoromethane as a simple example of a chiral molecule. The two enantiomers of BrCIFCH are shown as ball-and-stick models, as wedge-and-dash drawings, and as Fischer projections in Figure 7.6. Fischer projections are always generated the same way the molecule is oriented so that the vertical bonds at the chirality center are directed away from you and the horizontal bonds point toward you. A projection of the bonds onto the page is a cross. The chirality center lies at the center of the cross but is not explicitly shown. 

FIGURE 7.6 Ball-and-spoke models (/eft), wedge-and-dash drawings (center), and Fischer projections (right) of the R and S enantiomers of bromochlorofluoromethane. 

Table 24. Solvent dependence of2JH F of bromochlorofluoromethane in various solvents ( mole fraction CHBrCIF = 0.05)...

Notice in Figure 7.1c, where the two enantiomers of bromochlorofluoromethane are similarly oriented, that the difference between them corresponds to an interchange of the positions of bromine and chlorine. It will generally be true for species of the type C(w, x, y, z), where w, x, y, and z are different atoms or groups, that an exchange of two of them converts a structure to its enantiomer, but an exchange of three returns the original structure, albeit in a different orientation. 

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