KINETICS vs. THERMODYNAMICS

15/07/2017

Where I am Problems and exercises Molecular panel Home

Chemical reactions can be governed by the rate -speed- at which the reaction products are formed or by the relative stability of the latter.

Let me apologize for the joke. The situation is conceptually close to the act of stealing . How come?
Just compare a simple shoplifting with a big robbery. The first can be made quickly but it won't render you richly stable. In turn, the second is much slow to be planned but will make you definitely much richer.
Do you catch
the idea?

Using chemical language, one could say that the 'shoplifting' is KINETICALLY CONTROLLED, because we 'steal a given object' very quickly indeed.
In contrast, the big robbery is not kinetically controlled - it implies the planning of slow, complex logistics - 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 to the primary position, much more abundant and accesible - kind of 'shoplifting'.
C: Attack to the tertiary position, unique and less accesible - needs the planning of the big robbery.
D: Primary radical, much more unstable.
E: Tertiary radical, much less unstable.