Under comparable conditions the three halogens $F X_{2}$ , $Cl X_{2}$ and $Br X_{2}$ all halogenate an alkane through radicals. Which one gives a product distribution closest to the purely statistical one (number of H of each kind)?

A $F X_{2}$
Ball three give the same distribution
C $Cl X_{2}$
D $Br X_{2}$

Answer: A

F X^{∙}

is the most reactive and its hydrogen abstraction is very exothermic with a very early transition state. It therefore hardly distinguishes between C-H bonds, and the product ratio follows the statistical factor. Selectivity increases in the order

F X_{2} < Cl X_{2} < Br X_{2}

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Under comparable conditions the three halogens FX2​, ClX2​ and BrX2​ all halogenate an alkane through radicals. Which one gives a product distribution closest to the purely statistical one (number of H of each kind)?

Answer: A

More questions on Hammond postulate and reactivity-selectivity

Under comparable conditions the three halogens $F X_{2}$ , $Cl X_{2}$ and $Br X_{2}$ all halogenate an alkane through radicals. Which one gives a product distribution closest to the purely statistical one (number of H of each kind)?