30.5: Anchimeric Assistance by Other Neighboring Groups
- Page ID
- 44004
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Double Bonds |
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Triple Bonds |
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Sulfur Atoms |
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Oxygen Atoms |
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Nitrogen Atoms |
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Examples of other neighboring group perturbations, including non-bonding electron pair assistance by neighboring sulfur, oxygen and nitrogen atoms will be displayed above by clicking the appropriate button under the diagram. The text box commentary will change to suit the examples. In most of the cases involving heteroatom assistance, an "onium" intermediate is formed, in which the heteroatom is charged. Adjacent halogen atoms may also stabilize carbocations, as noted earlier with respect to trans-anti additions to cyclic alkenes. Functional rearrangement by way of halonium intermediates has also been reported. For example, a chloroform solution of the diaxial 2-bromo-3-chlorosteroid, shown on the left below, spontaneously rearranges to the more stable diequatorial 2-chloro-3-bromo isomer drawn on the right. The rearrangement is reversible and proceeds by way of the cyclic bromonium ion written in brackets.