Chirality of Compounds With A Stereogenic "lone Pair"
When a nonbonding pair of electrons, a lone pair, occupies space, chirality can result. The effect is pervasive in certain amines, phosphines, sulfonium and oxonium ions, sulfoxides, and even carbanions. The main requirement is that aside from the lone pair, the other three substituents differ mutually. Chiral phosphine ligands are useful in asymmetric synthesis.
Chiral amines (see images) are special in the sense that the enantiomers can rarely be separated. The energy barrier for nitrogen inversion of the stereocenter is generally about 30 kJ/mol, which means that the two stereoisomers rapidly interconvert at room temperature. As a result, such chiral amines cannot be resolved into individual enantiomers unless some of the substituents are constrained in cyclic structures as in Tröger's base.
Read more about this topic: Chirality (chemistry)
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