Reactivity: How and Why - Organic Chemistry Concepts: An EFL Approach - page 68

5.3.1 Carbon Radicals, Carbocations, and Carbanions
Most organic chemical reactions occur at carbon. Therefore, it is very impor-
tant to understand the features of carbon-based reactive species. To deal with
the reactions of these species, you need to be able to classify them. To do this,
you need to understand the factors that control their formation and stability,
because this will determine their reactivity.

The major factors are the concepts of inductive effect and resonance/delocaliza-
tion. The greater these effects, the greater the stability, and the easier it is for the
species to form.

5.3.1.1 CARBON RADICALS
As seen in Figure 5.3 , radicals are formed by homolytic bond breaking. With
only three ligands, radicals try to have a planar sp 2 shape. Stability is determined
by the ability of the attached ligands to feed electron density to the electron-
poor radical center. Electron donation is by either inductive effects or resonance/
delocalization.

Inductive effects.

n

This gives a general stability order of 3° > 2° > 1°.

Resonance/delocalization.

n

5.3.1.2 CARBOCATIONS
As seen in Figure 5.3 , carbocations are formed by heterolytic bond breaking.
With only three ligands, they also try to have a planar sp 2 shape. Stability is
determined by the ability of the attached ligands to feed electron density to the
electron-poor carbocation. Electron donation is by either inductive effects or
resonance/delocalization.

Inductive effects.

n

This gives a general stability order of 3° > 2° > 1°.