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9 Cards in this Set

  • Front
  • Back
An Aldehyde or ketone is converted into an alkene by means of the
Wittig rxn
In the Wittig rxn, a phosphorus ylide, R2C-P(C6H5)3) adds to an aldehyde or ketone to yield ..
a dipolar intermediate called a betaine
The betaine intermediate is not isolated, rather, it
spontaneously decomposes through a four membered ring to yield alkene and triphenylphosphine oxide
The net result of the betaine intermediate is the ...
replacement of the carbonyl oxygen atom by the R2C= group originally bonded to phosphorus
The phosphorus ylides necessary for Wittig rxn are easily prepared by?
Sn2 rxn of primary(and sometimes secondary) alkyl halides with triphenylphosphine, followed by treatment with base
Triphenylphine, (Ph)3P, is a good nucleophile in an Sn2 rxn, and yields of
the resultant alkyltriphenylphosphonium salts are high

- Cuz of the positive charge on the phosphorus, the hydrogen on the neighboring carbon is weakly acidic and can be removed by a base such as butyllithium (BuLi) to generate the neutral ylide
The Wittig rxn is extremely general in its applications, and a great many mono-, di-, and tri- substituted alkenes can be ...
prepared from the appropriate combo of phosphorane and aldehyde or ketone
The real value of the Wittig rxn is that it yields a ?
pure alkene of known structure.
The C=C bond of the Wittig Rxn in the product is always...
exactly where the C=O group was in the reactant, and no alkene isomers (except E,Z isomers) are formed