13

equilibrium is determined by the difference in energy according to:

∆G = -RT lnK

2.4.

Halogenation

General reaction scheme:

Electrophile:

X+

generated from Lewis acid (halogen carrier) and molecular hydrogen

Mechanism:

Halogenation does not suffer from ß-substitution. The α-substituted product is more
stable and since the reaction is reversible it is the major product under thermodynamic
conditions.

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Br

Br

FeBr3

Br

Br

FeBr3

H
Br

H
Br

Br

Br2

FeBr3

+

FeBr4

+

slow

fast

r.d.s.

+

H+