Organic Chemistry - Carbocations

Carbocations

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CARBOCATIONS

 

A species containing a positively charged carbon atom is called a carbocation (Fig. I.1). For many years these species were called "carbonium ions". In the early seventies George Olah proposed that the name "carbonium ion" should be reserved for pentacoordinated positive ions and that carbocations should be named "carbenium ions". Carbocations and their reactivity play an important role in chemistry since these species are intermediates in several kinds of reactions.

The more stable ones have been prepared in solution and in some cases even as solid salts. The less stable ones (more reactive) react in solution to produce new products.

Fig. I.1: General formula of a carbocation

By definition, every carbocation is an electron deficient species since it possesses a positive charge at a carbon atom. Carbocations are by their very nature unstable species.

Anything which donates electron density to the electron-deficient center will help to stabilize them.

Factors that stabilize them are the following:

  • Neighboring carbon atoms (inductive effect)
  • Neighboring carbon-carbon multiple bonds (resonance effect)
  • Neighboring atoms with lone pairs (resonance effect)

These factors are presented in the above posts and their stabilizing effect is explained.

 

References

  1. R. Bruckner, “Advanced Organic Chemistry – Reaction Mechanisms”, 2nd Edition, Elsevier, 2002

  2. M.B. Smith & J. March “March’s Advanced Organic Chemistry”, 6th Edition, Wiley-Interscience, 2007

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