Equatorial lone pair

It is readily recognized that the conformation in which the lone pair is equatorial corresponds to an anti-arrangement of the carbon lone pair in relation to the adjacent S—C bond (darkened for the sake of clarity) and the axial case a syn orientation. Based on our approach, we would predict that the carbanion with the lone pair equatorial will be the most stable conformation. This is indeed observed experimentally361. ... 

By the same reasoning, we understand why additional lone pairs also take equatorial positions (AB3U2 with both lone pairs equatorial or AB2U3 with all three lone pairs equatorial). These arrangements are summarized in Figure 8-2. 

BrF2 has two bonds and three lone pairs on the central atom. The hybridization is sp d. The electron geometry is trigonal bipyramidal with the three lone pairs equatorial. The molecular geometry is linear. 

In the solid state, PhaSbOAc has a distorted trigonal bipyramidal structure phenyl groups and lone-pair equatorial with bonded oxygen (Sb-O 213.7) and bridging oxygen (Sb-O 259.2, 251.3) axial. In solution the aggregation breaks down. ... 

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