Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions C↔XT Ph₂p-CHCH3 H3C :0: CH3 H3C :: PPh3 Et H -CH3 ча

Chemistry
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Chapter1: Chemical Foundations
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CH3
Ph3P-CHCH3
H3C
H3C
Aldehydes and ketones are converted into alkenes by means of a direct nucleophilic addition called the Wittig reaction. In the reaction, a triphenylphosphorine ylide, also called a phosphorane, adds to
an aldehyde/ketone to give a four-membered cyclic intermediate called an oxaphosphetane. The oxaphosphetane is not isolated but instead spontaneously decomposes to release triphenylphosphine
oxide and an alkene.
Ph3P-CHCH3
H3C
The ylide is formed by reaction of triphenylphosphine, a good nucleophile, with a primary alkyl halide in an S 2 reaction, followed by deprotonation of the carbon with a strong base, such as
butyllithium. The carbonyl carbon and the carbon originally bonded to the halogen become the two carbons with the double bond in the product alkene
:0:
CH3
Com
The real value of the Wittig reaction lies in its ability to yield an alkene of predictable structure, as the C-C bond is precisely where the C=O bond was in the reactant and no isomers (other than E/Z
isomers) are formed.
Draw curved arrows to show the movement of electrons in this step of the mechanism.
Arrow-pushing Instructions
NOC XT
CH3
H3C
CH3
Et
:: PPh3
H
Ph3P=O
-CH3
ча
Transcribed Image Text:CH3 Ph3P-CHCH3 H3C H3C Aldehydes and ketones are converted into alkenes by means of a direct nucleophilic addition called the Wittig reaction. In the reaction, a triphenylphosphorine ylide, also called a phosphorane, adds to an aldehyde/ketone to give a four-membered cyclic intermediate called an oxaphosphetane. The oxaphosphetane is not isolated but instead spontaneously decomposes to release triphenylphosphine oxide and an alkene. Ph3P-CHCH3 H3C The ylide is formed by reaction of triphenylphosphine, a good nucleophile, with a primary alkyl halide in an S 2 reaction, followed by deprotonation of the carbon with a strong base, such as butyllithium. The carbonyl carbon and the carbon originally bonded to the halogen become the two carbons with the double bond in the product alkene :0: CH3 Com The real value of the Wittig reaction lies in its ability to yield an alkene of predictable structure, as the C-C bond is precisely where the C=O bond was in the reactant and no isomers (other than E/Z isomers) are formed. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions NOC XT CH3 H3C CH3 Et :: PPh3 H Ph3P=O -CH3 ча
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