12

Kinetic vs Thermodynamic Control

when naphthalene is sulphonated two different products are isolated depending on the
reaction conditions used:

kinetic product

thermodynamic product

•
•

naphthalene is more reactive than benzene
it reacts faster in α-position (only two possible sites of attack)

more resonance forms in which the other benzene ring is not disrupted:
these are major contributing canonicals

but for b-attack only 1resonance form which does not destroy the second aromatic
ring is available:

However, a-substitution suffers from periinteraction with the hydrogen atom at C8

IMAGE aromatics232.gif
IMAGE aromatics233.gif

SO3H

SO3H

80oC
conc. H2SO4

160oC
conc. H2SO4

160oC
conc. H2SO4

IMAGE aromatics234.gif
IMAGE aromatics235.gif
IMAGE aromatics236.gif
IMAGE aromatics237.gif
IMAGE aromatics238.gif
IMAGE aromatics239.gif
IMAGE aromatics240.gif
IMAGE aromatics241.gif

H

SO3H

IMAGE aromatics242.gif

SO3H

SO3H

conc. H2SO4

E

Reaction coordinate