Advices For Studying Organic Chemistry

A Mechanism for the Reaction

Oxymercuration

Step 1 Hg(OAc) 2 +HgOAc + –OAc

Mercuric acetate dissociates to form an Hg+OAc ion and an acetate ion.

Step 2

H 3 C CCH

CH 3

CH 3

CH 2 Hg+OAc H 3 C C

CH 3

CH 3

CH CH 2

HgOAc

+

δ+

3,3-Dimethyl-1-butene

δ+

Mercury-bridged carbocation

The electrophilic HgOAc+ ion accepts a pair of electrons from the alkene to form a

mercury-bridged carbocation. In this carbocation, the positive charge is shared

between the 2° carbon atom and the mercury atom. The charge on the carbon

atom is large enough to account for the Markovnikov orientation of the addition,

but not large enough for a rearrangement to occur.

Step 3

O

H

H

H 3 C C

CH 3

CH 3

CH CH 2

HgOAcδ+

δ+ H^3 C C

CH 3

CH 3

CH CH 2

HgOAc

OH+ 2

A water molecule attacks the carbon bearing the partial positive charge.

Step 4

H O

OH+ 2 OH

H

H 3 C C + H

CH 3

CH 3

CH CH 2

HgOAc

O

H

H

H 3 C C

CH 3

CH 3

CH CH 2

HgOAc

+

(Hydroxyalkyl)mercury compound

An acid-base reaction transfers a proton to another water molecule (or to an acetate

ion). This step produces the (hydroxyalkyl)mercury compound.

(^)

8. Mercury compounds are extremely hazardous.