# What is the Major product in free radical halogenation of Alkanes. (Between 3°,2°,1°) [closed]

In Free Radical Halogenation in presence of sunlight, a no. Of products are possible.

Due to higher stability of a 3°(Tertiary) radical, 3° products should be favored. But another factor that comes is that the formation of 3 ° radicals also leads to higher disproportion products. (Radical Disproportion- https://en.m.wikipedia.org/wiki/Radical_disproportionation)

Now, if i look at the intermediate, a higher no. Of Tertiary Radicals should form. But a lot of them will undergo radical disproportion as it is fastest in tertiary radical.

So is there any clear order of what product should be major or does it vary from case to case?

## closed as unclear what you're asking by Mithoron, aventurin, A.K., a-cyclohexane-molecule, Todd MinehardtSep 20 '18 at 23:38

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• What do you mean by "disproportion products"? – Tan Yong Boon Sep 19 '18 at 5:39
• Where did you find this nomenclature with the degree sign for primary, secondary, tertiary? – Karl Sep 19 '18 at 7:17
• @Tan Yong Boon en.m.wikipedia.org/wiki/Radical_disproportionation – Groverkss Sep 23 '18 at 16:06
• @Karl I frequently saw this nomenclature in Organc Chemistry by Solomans and Fryhle. – Groverkss Sep 23 '18 at 16:09

It depends on what halogen you use.

Chlorine has a reactivity ratio for $1^o$:$2^o$:$3^o$= 1 : 3.5 : 5.

To calculate the relative yield at that position, multiply the number of Hydrogens at that position to the reactivity at that position. This will give you a comparison of the yield at particular positions.

But in the case of bromine, the reactivity order is 1 : 250 : 6300. Therefore, without any further thinking, the bromine radical will always attack at the tertiary position if available.

In general, reactivity towards tertiary carbon increases down the group as in the case of halogens.

• This does not solve my problem. I do know the reactivity order. But i am confused in the major product as much of the Tertiary radical will undergo disproportion. – Groverkss Sep 23 '18 at 16:17

It all depends on the halogen that is being used. The more reactive ones like chlorine don't really show stereo-selectivity whereas the less reactive ones like bromine do show the expected selectivity: 3°, 2°, 1°