Carbocations and carbanions are two types of reactive intermediates in organic chemistry, and they differ primarily in their charge, structure, and stability.
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Charge:
- Carbocations: Positively charged species with a carbon atom bonded to three other groups or atoms and carrying a positive charge due to having only six valence electrons (electron deficiency).
- Carbanions: Negatively charged species with a carbon atom bonded to three other groups or atoms and carrying a negative charge due to possessing an extra pair of electrons (electron richness).
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Hybridization and Geometry:
- Carbocations: Typically sp² hybridized, leading to a trigonal planar geometry around the charged carbon atom.
- Carbanions: Generally sp³ hybridized, resulting in a tetrahedral geometry around the carbon atom with the negative charge.
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Stability:
- Carbocations: Stability increases with the degree of alkyl substitution (tertiary > secondary > primary), as electron-donating alkyl groups help to stabilize the positive charge through hyperconjugation and inductive effects.
- Carbanions: Stability is influenced by electronegativity and the ability to stabilize the negative charge. More stable with fewer alkyl substituents (primary > secondary > tertiary) and can be stabilized by resonance or induction from electronegative groups.
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Reactivity:
- Carbocations: Highly reactive due to electron deficiency; they readily participate in nucleophilic attacks.
- Carbanions: Also reactive, but act as nucleophiles, seeking to donate their extra electron pair.
In summary, carbocations are positively charged, electron-deficient intermediates that are generally stabilized by nearby alkyl groups, while carbanions are negatively charged, electron-rich species often destabilized by bulkier groups.