Ch_322a_11.05

Ch_322a_11.05 - at the carbon with the greater positive...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
A Mechanism for the Oxymercuration-Demercuration Reaction There is general agreement the reaction begins with electrophilic attack of mercury (II), possibly as + Hg(OAc), on the ! -bond of the alkene. (1) Hg(OAC) 2 Hg-OAc + + OAc - (2) CH 3 -C-CH=CH 2 CH 3 CH 3 + Hg-OAc + an electrophile C C (CH 3 ) 3 C H H H Hg OAc + A bridging mercurinium ion is believed to form rather than a free carbocation since typical carbocation rearrangements do not occur.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
A Closer Look at the Mercurinium Ion The dotted lines in the mercurinium ion means partial bonds. The two electrons donated by the ! -bond are distributed as shown in the following resonance structures: C C (CH 3 ) 3 C H H Hg OAc + H C C (CH 3 ) 3 C H H H Hg OAc + C C (CH 3 ) 3 C H H H Hg OAc + C C (CH 3 ) 3 C H H H Hg OAc + I II III major contributions Calculations show that much of the positive charge resides on the mercury (as in I ) with most of the rest on the secondary carbon in II .
Background image of page 2
Regioselective Reaction of the Mercurinium Ion The mercurinium ion reacts with a nucleophile (H 2 O) preferentially
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: at the carbon with the greater positive charge density: C C (CH 3 ) 3 C H H Hg OAc + H (3) + H 2 O : : (CH 3 ) 3 C-CH-CH 2-Hg-OAc OH 2 + (4) (CH 3 ) 3 C-CH-CH 2-Hg-OAc O-H + + H 2 O: H fast (CH 3 ) 3 C-CH-CH 2-Hg-OAc O-H + + H 3 O oxymercuration product At this stage the regiochemistry is set. Reduction yields the Markovnikov product. Reduction of the Oxymercuration Product (5) (CH 3 ) 3 C-CH-CH 2-Hg-OAc O-H + H-B-H H H-Na + Reaction is shown as a two-electron reduction. sodium borohydride (CH 3 ) 3 C-CH-CH 3 O-H + Hg o + CH 3 CO 2-3,3-dimethyl-2-butanol (Markovnikov Addition Product) Reduction of the alkylmercury acetate with sodium borohydride is not a well defined reaction. A free radical may be involved. The net result is reductive cleavage of the C-Hg(II) bond by hydride, replacing the metal with H, and producing Hg(0)....
View Full Document

This note was uploaded on 07/22/2009 for the course CHEM 322AL taught by Professor Jung during the Summer '07 term at USC.

Page1 / 4

Ch_322a_11.05 - at the carbon with the greater positive...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online