Kinetics vs. Thermodynamics
Chemical reactions can be governed by the rate at which the products are formed or by the relative stability of the latter.
Forgive the joke, but the situation is conceptually similar to stealing. Compare a simple act of shoplifting with a big robbery: the first is quick but will not make you lastingly rich; the second is much slower to plan but will make you far richer. Do you get the idea?
Using chemical language, one could say that the 'shoplifting' is KINETICALLY CONTROLLED, because we 'steal an object' very quickly. In contrast, the big robbery is not kinetically controlled - it requires slow, complex planning - but THERMODYNAMICALLY CONTROLLED because it makes you slowly but stably rich.
Could we apply this scheme to the halogenation of alkanes? A: X2 + methylbutane
B: Attack at the primary positions, much more abundant and accessible - kind of 'shoplifting'. C: Attack at the tertiary position, unique and less accessible - needs the planning of the big robbery. D: Primary radical, much more unstable. E: Tertiary radical, much less unstable.
