Is this DAT Achiever question incorrect?

[AT12]

Practice exam #3, problem 99 (orgo)

(CH3)2CHCH2CH3 reacted with Cl2 and hv

DAT achiever says the answer is (CH3)2CClCH2CH3 (forming the most stable radical)

However, according to Kaplan, when Cl2 radical reacts, does not depend on the stability of the intermediate, but on the # of hydrogens present. Kaplan says Cl radicals are more likely to replace primary H.

So, I think the answer is replacing one of the H of the CH3 groups on the left of the molecule.

Is this correct??

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[jessica22]

I am pretty sure it is correct. with Br2 free radical, u're forming the most stable free radical. But with Chlorination free radical, you're going to have both the least stable one and the most stable one..

I am not sure if I answered your question, but that was from O-chm 2 years ago... hope other will help...

 

[Gasedo]

Yes, jessica 22 is correct. What kaplan explains is that free radical halogenation reactions are for Br and Cl only. I and F cannot react. Br radicals react very slowly in comparison to Cl radicals, so they are most likely to react forming the most stable alkyl radical, i.e. 3.
So you get one major bromination product. Cl radicals react so quickly that they become rather indiscriminate, and generally produce several different products.
Hope this helps.

 

[jessica22]

Gasedo, you're good

 

[AT12]

Gasedo, you're good

Thanks!

 

[dat_student]

Practice exam #3, problem 99 (orgo)

(CH3)2CHCH2CH3 reacted with Cl2 and hv

DAT achiever says the answer is (CH3)2CClCH2CH3 (forming the most stable radical)

However, according to Kaplan, when Cl2 radical reacts, does not depend on the stability of the intermediate, but on the # of hydrogens present. Kaplan says Cl radicals are more likely to replace primary H.

So, I think the answer is replacing one of the H of the CH3 groups on the left of the molecule.

Is this correct??

1st step of radical reactions should give you the most stable radical. More stable intermediates are formed faster (lower activation energy). So you get more of them

Kaplan: double bond + Cl2 + hv
Cl reacts with the less hindered side of the double bond (i.e.the side with more H atoms) to form the most stable radical.

This question >> NO double bond + Cl2 + hv
Cl extracts a proton 1st to form the most stable radical and then the second Cl reacts with the most stable radical