Antarafacial, definition

Recall now our definition (p. 599) of a component as a noncyclic chain of interacting basis orbitals with signs chosen so that no internal phase inversions occur. Components may contain either an even or an odd number of basis orbitals, but we are restricting the discussion to systems with an even number of electrons and may therefore require that the number of electrons contributed by a component be even.51 A component may enter into interaction with other components at its ends in either a suprafacial way, if the signs of the interacting lobes at the two ends are the same, or in an antarafacial way if the signs of the interacting lobes are opposite. There are thus four types of components (4q)s, (4q)a, (4q + 2)j, and (4q + 2)a. 

For TT systems and lone pairs the distinction is simple suprafadal interactions involve the same face of the system, while antarafacial interactions are on opposite faces. Although we have only examined tt systems thus far, we will examine pericyclic reactions below that involve a bonds. Therefore, we need a similar definition for these kinds of bonds. For a bonds, the distinction is less obvious, but is consistent with the other systems. With suprafa-cial interactions, the two loops are drawn to either the inner lobes or outer lobes, while with an antarafacial interaction one loop is to an inner and one is to an outer lobe (see Figure 15.9 for this to make sense). Note that a suprafacial interaction at a cr bond involving two sp hy-... 

Definitions of suprafacial and antarafacial for various types of orbitals. 

Figure 15.9 defined suprafacial and antarafacial interactions of a lone pair in a p orbital (called an uj component). Using these definitions, predict if the ring-opening of the cyclopropyl anion shown below will occur in a conrotatory or disrotatory fashion. What will be the stereochemistry of the product ... 

Suprafacial and antarafacial cycloadditions have their definite stereochemical consequences which can be made clear through the following examples ... 

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