Organic Chemistry - Reaction Intermediates



In Organic Chemistry generally, there are three types of reaction intermediates ,which are 


Carbocations:


  • Definition: Carbocations are positively charged carbon species, where carbon has only three bonds and a vacant p orbital.
  • Formation: They are formed by the loss of a leaving group, resulting in an electron-deficient carbon atom.
  • Stability: Carbocations follow the order of stability: tertiary > secondary > primary > methyl. Stability is determined by hyperconjugation and inductive effects.
  • Reactivity: Being electron-deficient, carbocations are highly reactive and act as electrophiles, seeking electrons from nucleophiles to achieve stability.
  • Examples: Examples include methyl carbocation (CH₃⁺), ethyl carbocation (C₂H₅⁺), etc.

Carbanions:
    • Definition: Carbanions are negatively charged carbon species, where carbon has three bonds and one lone pair of electrons.
    • Formation: They are formed by the addition of a nucleophile to a carbon with a leaving group, resulting in an electron-rich carbon atom.
    • Stability: Carbanions follow the order of stability: methyl < primary < secondary < tertiary. Stability is determined by factors like resonance and inductive effects.
    • Reactivity: Carbanions act as nucleophiles, attacking electrophiles to form new bonds. They are often involved in SN2 reactions.
    • Examples: Examples include methyl carbanion (CH₃⁻), ethyl carbanion (C₂H₅⁻), etc.

Free Radicals:


  • Definition: Free radicals are neutral species possessing an unpaired electron, making them highly reactive.
  • Formation: Free radicals are formed by homolytic cleavage of covalent bonds, resulting in the separation of a shared pair of electrons, leaving each atom with one electron.
  • Stability: Unlike carbocations and carbanions, free radicals don't exhibit a straightforward stability trend. However, resonance and hyperconjugation can stabilize them to some extent.
  • Reactivity: Free radicals act as both electrophiles and nucleophiles, participating in various radical reactions such as radical halogenation, polymerization, and radical substitution.
  • Examples: Examples include methyl radical (CH₃•), ethyl radical (C₂H₅•), etc.

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