Which statements concerning reactivity and selectivity in radical halogenation are correct?

AIn general the more reactive a halogen radical is, the less selective it is.
B $Br X^{∙}$ is less selective than $F X^{∙}$ .
CSelectivity of radical chlorination usually decreases as the temperature is raised.
DThe large preference of $Br X^{∙}$ for tertiary C-H arises because its late transition state feels most of the difference between radical stabilities.

Answer: A, C, D

The reactivity-selectivity principle holds well for the halogen radicals:

F X^{∙}

is the most reactive and least selective,

Br X^{∙}

the least reactive and most selective, so statement 2 is wrong. A higher temperature reduces the effect of small differences in

E_{a}

, so selectivity drops (statement 3). Statement 4 is the Hammond-postulate explanation. Answer: 1, 3 and 4.