Alkanes and radicals 2: Product spread

Alkanes & radicals

Relative stabilities of alkyl radicals

Alkyl groups stabilize carbocations about 5 to 10 times better than when alkyl groups have to stabilize radicals:

Radicals: Resonance >> Hyperconjugation

Carbocations: Hyperconjugation >> Resonance

Hyperconjugation makes the carbocations more stabilized than when hyperconjugation occurs with radicals (not so stable). This is explained due to the fact that in carbocations, both electrons sit in the same binding orbital, with radicals however, one of the electrons is sited in the anti-binding orbital.

Product spread

The product spread (product outcome) is determined by CHANCE and REACTIVITY. The chance (or probability) is based on the relative amount of primary and secundary protons (in the example below 6:4), but secundary hydrogens are more reactive than primary hydrogens, this means both chance and reactivity determine the outcome of the reaction.

Thus to determine the product spread, both chance and intrinsic reactivity have to be considered:

Probabillity: the amount of hydrogens that can be removed to lead to a certain product.
Reactivity: the relative rate with what a hydrogen gets removed.

Some examples of chlorationproducts found below. Radical chlorationreactions are less selective than reactions via a carbocation intermediate.

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