[x-disturbed-x]

Hi, can anyone help me with this question? Not sure how to answer it. I know in homolytic (thermal) cracking an alkene is produced as below, doubt that's all you need to know in order to answer it. Any help is appreciated. 

Cracking of hydrocarbons involves breaking c-c bonds. This involves either homolytic fission (free radicals) or heterolytic fission (carbocation ans carboanion).

Industrial cracking of decane produces a branched chain alkane as one of its products e.g.

C10H22 ---> CH3CH2CH=CH2 + CH3CH(CH3)CH2CH2CH3
decane ---> butene + 2-methylpentane

Use this observation to assess which of the two mechanisms is involved in this reaction. (Draw out structural formula of intermediates to illustrate your answer).

(Clue - relative stability of intermediate).

[kiwi]

the clue pretty much gives it away. what factors stabilise a carbocation, and what factors stabilise a radical?

[x-disturbed-x]

electrophiles stabilise carbocatios and nucleophiles stabilise free radicals..there's no lightbulb flashing in my head..or am i wrong 

[kiwi]

carbocation stability: tertiary>secondary>primary. illuminated?

[x-disturbed-x]

eh not really, what are the intermediates?

[kiwi]

you're getting close. consider carbanion stability: primary>secondary>tertiary. if the fisson is homolytic, what types of products would you expect?

[x-disturbed-x]

free radicals?

[x-disturbed-x]

seriously this might sound stupid but what actually are the intermediates?

[kiwi]

they're the intermediates you'd expect, not the final products. if you form a primary radical, it will very quickly (in the absence of any stabilising effects) rearrange to a more stable radical - in this case secondary. but both radicals will rearrange in the same way, leading to two similar products. if you form a primary carbanion and carbocation, one of them will rearrange to a more a stable form, the other will stay in its stable primary form, ultimately leading to two different types of products. see now?

[x-disturbed-x]

nein, not at all. i'll see my teacher about it, thanks for the help 

[kiwi]

no problem, beats doing another column