Carbocations are generally considered more stable than carbanions due to their structural characteristics and electron-donating effects. For instance, the tert-butyl carbocation ((CH3)3-C+) benefits from stabilization through three methyl groups that donate electrons, effectively stabilizing the positive charge. In contrast, the tert-butyl carbanion ((CH3)3-C-) is less stable and more reactive because the negatively charged carbon is sp3 hybridized, resulting in a tetrahedral structure. This configuration leads to increased reactivity, as the lone pair of electrons in the fourth sp3 orbital can contribute to radical behavior. Additionally, carbocations tend to rearrange quickly in solution, while carbanions can remain intact after generation, but their overall stability is still lower compared to carbocations.
